| 1. |
- Adman, Per, et al.
(författare)
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171 forskare: ”Vi vuxna bör också klimatprotestera”
- 2019
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Ingår i: Dagens nyheter (DN debatt). - Stockholm. - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 26/9. Vuxna bör följa uppmaningen från ungdomarna i Fridays for future-rörelsen och protestera eftersom det politiska ledarskapet är otillräckligt. Omfattande och långvariga påtryckningar från hela samhället behövs för att få de politiskt ansvariga att utöva det ledarskap som klimatkrisen kräver, skriver 171 forskare i samhällsvetenskap och humaniora.
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| 2. |
- Gaccioli, F., et al.
(författare)
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Expression and functional characterisation of System L amino acid transporters in the human term placenta
- 2015
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Ingår i: Reproductive Biology and Endocrinology. - : Springer Science and Business Media LLC. - 1477-7827. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Background: System L transporters LAT1 (SLC7A5) and LAT2 (SLC7A8) mediate the uptake of large, neutral amino acids in the human placenta. Many System L substrates are essential amino acids, thus representing crucial nutrients for the growing fetus. Both LAT isoforms are expressed in the human placenta, but the relative contribution of LAT1 and LAT2 to placental System L transport and their subcellular localisation are not well established. Moreover, the influence of maternal body mass index (BMI) on placental System L amino acid transport is poorly understood. Therefore the aims of this study were to determine: i) the relative contribution of the LAT isoforms to System L transport activity in primary human trophoblast (PHT) cells isolated from term placenta; ii) the subcellular localisation of LAT transporters in human placenta; and iii) placental expression and activity of System L transporters in response to maternal overweight/obesity. Methods: System L mediated leucine uptake was measured in PHT cells after treatment with si-RNA targeting LAT1 and/or LAT2. The localisation of LAT isoforms was studied in isolated microvillous plasma membranes (MVM) and basal membranes (BM) by Western blot analysis. Results were confirmed by immunohistochemistry in sections of human term placenta. Expression and activity System L transporters was measured in isolated MVM from women with varying pre-pregnancy BMI. Results: Both LAT1 and LAT2 isoforms contribute to System L transport activity in primary trophoblast cells from human term placenta. LAT1 and LAT2 transporters are highly expressed in the MVM of the syncytiotrophoblast layer at term. LAT2 is also localised in the basal membrane and in endothelial cells lining the fetal capillaries. Measurements in isolated MVM vesicles indicate that System L transporter expression and activity is not influenced by maternal BMI. Conclusions: LAT1 and LAT2 are present and functional in the syncytiotrophoblast MVM, whereas LAT2 is also expressed in the BM and in the fetal capillary endothelium. In contrast to placental System A and beta amino acid transporters, MVM System L activity is unaffected by maternal overweight/obesity.
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| 3. |
- Jansson, Nina, 1976, et al.
(författare)
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Activation of Placental mTOR Signaling and Amino Acid Transporters in Obese Women Giving Birth to Large Babies.
- 2013
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Ingår i: The Journal of clinical endocrinology and metabolism. - : The Endocrine Society. - 1945-7197 .- 0021-972X. ; 98:1, s. 105-13
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Tidskriftsartikel (refereegranskat)abstract
- Context: Babies of obese women are often large at birth, which is associated with perinatal complications and metabolic syndrome later in life. The mechanisms linking maternal obesity to fetal overgrowth are largely unknown. Objective: We tested the hypothesis that placental insulin/IGF-I and mammalian target of rapamycin (mTOR) signaling is activated and amino acid transporter activity is increased in large babies of obese women. Design and Setting: Pregnant women were recruited prospectively for collection of placental tissue at a university hospital and academic biomedical center. Patients or Other Participants: Twenty-three Swedish pregnant women with first trimester body mass index ranging from 18.5 to 44.9 kg/m(2) and with uncomplicated pregnancies participated in the study. Interventions: There were no interventions. Main Outcome Measures: We determined the phosphorylation of key signaling molecules (including Akt, IRS-1, S6K1, 4EBP-1, RPS6, and AMPK) in the placental insulin/IGF-I, AMPK, and mTOR signaling pathways. The activity and protein expression of the amino acid transporter systems A and L were measured in syncytiotrophoblast microvillous plasma membranes. Results: Birth weights (range, 3025-4235 g) were positively correlated to maternal body mass index (P < 0.05). The activity of placental insulin/IGF-I and mTOR signaling was positively correlated (P < 0.001), whereas AMPK phosphorylation was inversely (P < 0.05) correlated to birth weight. Microvillous plasma membrane system A, but not system L, activity and protein expression of the system A isoform SNAT2 were positively correlated to birth weight (P < 0.001). Conclusions: Up-regulation of specific placental amino acid transporter isoforms may contribute to fetal overgrowth in maternal obesity. This effect may be mediated by activation of insulin/IGF-I and mTOR signaling pathways, which are positive regulators of placental amino acid transporters.
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| 4. |
- Lindgren, Ulrika, et al.
(författare)
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Mitochondrial pathology in inclusion body myositis
- 2015
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Ingår i: Neuromuscular Disorders. - : Elsevier BV. - 0960-8966. ; 25:4, s. 281-288
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Tidskriftsartikel (refereegranskat)abstract
- Inclusion body myositis (IBM) is usually associated with a large number of cytochrome c oxidase (COX)-deficient muscle fibers and acquired mitochondrial DNA (mtDNA) deletions. We studied the number of COX-deficient fibers and the amount of mtDNA deletions, and if variants in nuclear genes involved in mtDNA maintenance may contribute to the occurrence of mtDNA deletions in IBM muscle. Twenty-six IBM patients were included. COX-deficient fibers were assayed by morphometry and mtDNA deletions by qPCR. POLG was analyzed in all patients by Sanger sequencing and C10orf2 (Twinkle), DNA2, MGME1, OPA1, POLG2, RRM2B, SLC25A4 and TYMP in six patients by next generation sequencing. Patients with many COX-deficient muscle fibers had a significantly higher proportion of mtDNA deletions than patients with few COX-deficient fibers. We found previously unreported variants in POLG and C10orf2 and IBM patients had a significantly higher frequency of an RRM2B variant than controls. POLG variants appeared more common in IBM patients with many COX-deficient fibers, but the difference was not statistically significant. We conclude that COX-deficient fibers in inclusion body myositis are associated with multiple mtDNA deletions. In IBM patients we found novel and also previously reported variants in genes of importance for mtDNA maintenance that warrants further studies. (C) 2014 Elsevier B.V. All rights reserved.
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| 5. |
- Oldfors Hedberg, Carola, 1969, et al.
(författare)
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Respiratory chain dysfunction in perifascicular muscle fibres in patients with dermatomyositis is associated with mitochondrial DNA depletion
- 2022
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Ingår i: Neuropathology and Applied Neurobiology. - : Wiley. - 0305-1846 .- 1365-2990. ; 48:7
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Tidskriftsartikel (refereegranskat)abstract
- Aims Patients with dermatomyositis (DM) suffer from reduced aerobic metabolism contributing to impaired muscle function, which has been linked to cytochrome c oxidase (COX) deficiency in muscle tissue. This mitochondrial respiratory chain dysfunction is typically seen in perifascicular regions, which also show the most intense inflammatory reaction along with capillary loss and muscle fibre atrophy. The objective of this study was to investigate the pathobiology of the oxidative phosphorylation deficiency in DM. Methods Muscle biopsy specimens with perifascicular COX deficiency from five juveniles and seven adults with DM were investigated. We combined immunohistochemical analyses of subunits in the respiratory chain including complex I (subunit NDUFB8), complex II (succinate dehydrogenase, subunit SDHB) and complex IV (COX, subunit MTCO1) with in situ hybridisation, next generation deep sequencing and quantitative polymerase chain reaction (PCR). Results There was a profound deficiency of complexes I and IV in the perifascicular regions with enzyme histochemical COX deficiency, whereas succinate dehydrogenase activity and complex II were preserved. In situ hybridisation of mitochondrial RNA showed depletion of mitochondrial DNA (mtDNA) transcripts in the perifascicular regions. Analysis of mtDNA by next generation deep sequencing and quantitative PCR in affected muscle regions showed an overall reduction of mtDNA copy number particularly in the perifascicular regions. Conclusion The respiratory chain dysfunction in DM muscle is associated with mtDNA depletion causing deficiency of complexes I and IV, which are partially encoded by mtDNA, whereas complex II, which is entirely encoded by nuclear DNA, is preserved. The depletion of mtDNA indicates a perturbed replication of mtDNA explaining the muscle pathology and the disturbed aerobic metabolism.
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| 6. |
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| 7. |
- Roos, Sara, 1979, et al.
(författare)
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A novel mitochondrial tRNA Arg mutation resulting in an anticodon swap in a patient with mitochondrial encephalomyopathy.
- 2013
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Ingår i: European journal of human genetics : EJHG. - : Springer Science and Business Media LLC. - 1476-5438 .- 1018-4813. ; 21:5, s. 571-3
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We report a mutation in the anticodon of the tRNA(Arg) gene (m.10437G>A), resulting in an anticodon swap from GCU to ACU, which is the anticodon of tRNA(Trp), in a boy with mitochondrial encephalomyopathy. Enzyme histochemical analysis of muscle tissue and biochemical analysis of isolated muscle mitochondria demonstrated cytochrome c oxidase (COX) deficiency. Restriction fragment length polymorphism analysis showed that 90% of muscle and 82% of urinary epithelium mtDNA harbored the mutation. The mutation was not identified in blood, fibroblasts, hair roots, or buccal epithelial cells and it was absent in the asymptomatic mother, suggesting that it was a de novo mutation. Single-fiber PCR analysis showed that the proportion of mutated mtDNA correlated with enzyme histochemical COX deficiency. This mutation adds to the three previously described disease-causing mutations in tRNA(Arg), but it is the first mutation occurring in the anticodon of tRNA(Arg).European Journal of Human Genetics advance online publication, 11 July 2012; doi:10.1038/ejhg.2012.153.
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| 8. |
- Roos, Sara, 1979, et al.
(författare)
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Expression of placental mammalian target of rapamycin (mTOR) is altered in relation to fetal growth and mTOR regulates leucine transport
- 2005
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Ingår i: Placenta. - 0143-4004. ; 26:8-9
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Konferensbidrag (refereegranskat)abstract
- Placental transport functions are altered in pregnancies complicated by restricted (IUGR) or accelerated fetal growth (LGA; large-for-gestational-age). We have suggested that the placenta may function as a nutrient sensor, regulating its nutrient transport in response to changes in substrate supply, and consequently altering fetal growth. mTOR is a protein kinase involved in regulating protein translation in response to nutrient stimuli. mTOR mRNA has been shown to be expressed in the placenta, its functional role however is unknown. To test the hypothesis that mTOR is involved in placental nutrient sensing we investigated mTOR protein expression in the human placenta in relation to fetal growth and we assessed the effect of the mTOR inhibitor rapamycin on amino acid transporter activity. Methods: mTOR expression was studied by immunohistochemistry and Western blotting and amino acid transporter activity was measured in term villous fragments. Results: mTOR protein was expressed in the cytoplasm of the syncytiotrophoblast. mTOR protein expression was up-regulated by 51% (p < 0.05) in homogenates of IUGR placentas (n = 9, controls n = 12) and down-regulated by 42% (p < 0.05) in placentas of LGA infants (n = 6, controls n = 15). Rapamycin (100 nM) decreased system L activity by 35% (n = 7, p < 0.05) but did not affect the activity of system A or taurine transporters. Conclusion: Placental mTOR protein expression is inversely related to fetal growth. Inhibition of placental mTOR decreases placental leucine transport, representing a novel regulatory mechanism for the L amino acid transporter. These findings are compatible with the hypothesis that the mTOR signaling system may play a role in placental nutrient sensing.
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| 9. |
- Roos, Sara, 1979, et al.
(författare)
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Expression pattern of mitochondrial respiratory chain enzymes in skeletal muscle of patients with mitochondrial myopathy associated with the homoplasmic m.14674T>C variant
- 2022
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Ingår i: Brain Pathology. - : Wiley. - 1015-6305 .- 1750-3639. ; 32:4
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Tidskriftsartikel (refereegranskat)abstract
- Two homoplasmic variants in tRNA(Glu) (m.14674T>C/G) are associated with reversible infantile respiratory chain deficiency. This study sought to further characterize the expression of the individual mitochondrial respiratory chain complexes and to describe the natural history of the disease. Seven patients from four families with mitochondrial myopathy associated with the homoplasmic m.14674T>C variant were investigated. All patients underwent skeletal muscle biopsy and mtDNA sequencing. Whole-genome sequencing was performed in one family. Western blot and immunohistochemical analyses were used to characterize the expression of the individual respiratory chain complexes. Patients presented with hypotonia and feeding difficulties within the first weeks or months of life, except for one patient who first showed symptoms at 4 years of age. Histopathological findings in muscle included lipid accumulation, numerous COX-deficient fibers, and mitochondrial proliferation. Ultrastructural abnormalities included enlarged mitochondria with concentric cristae and dense mitochondrial matrix. The m.14674T>C variant in MT-TE was identified in all patients. Immunohistochemistry and immunoblotting demonstrated pronounced deficiency of the complex I subunit NDUFB8. The expression of MTCO1, a complex IV subunit, was also decreased, but not to the same extent as NDUFB8. Longitudinal follow-up data demonstrated that not all features of the disorder are entirely transient, that the disease may be progressive, and that signs and symptoms of myopathy may develop during childhood. This study sheds new light on the involvement of complex I in reversible infantile respiratory chain deficiency, it shows that the disorder may be progressive, and that myopathy can develop without an infantile episode.
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| 10. |
- Roos, Sara, 1979, et al.
(författare)
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Histopathological changes in skeletal muscle associated with chronic ischaemia.
- 2016
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Ingår i: APMIS : acta pathologica, microbiologica, et immunologica Scandinavica. - : Wiley. - 1600-0463. ; 124:11, s. 935-941
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Tidskriftsartikel (refereegranskat)abstract
- Muscle biopsy is an essential part in the diagnostic workup in patients with suspected neuromuscular disorders. It is therefore important to be aware of morphological alterations that can be caused by systemic factors or natural ageing. Chronic limb ischaemia is frequent in elderly individuals. This study was performed to examine histopathological and mitochondrial changes in muscle in patients with chronic critical limb ischaemia. Muscle biopsy of skeletal muscle of the lower limb of patients with chronic ischaemia leading to amputation was performed and compared with muscle biopsies of healthy, age-matched controls. The histopathological abnormalities included fibrosis, necrosis, atrophy, glycogen depletion, internal nuclei, rimmed vacuoles, fibre type grouping, cytochrome c oxidase deficient fibres, MHC-I upregulation, and signs of microangiopathy. The only alteration found in age-matched controls was a few cytochrome c oxidase deficient fibres. There were also increased levels of multiple mitochondrial DNA deletions in ischaemic muscles compared with controls. Critical limb ischaemia is associated with significant histopathological changes in muscle tissue and also increased levels of mitochondrial DNA deletions. Since the alterations mimic different primary myopathic changes, chronic ischaemia is important to consider as a differential diagnosis in elderly individuals, investigated with muscle biopsy for muscle disease.
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| 11. |
- Roos, Sara, 1979, et al.
(författare)
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Human placental taurine transporter in uncomplicated and IUGR pregnancies: cellular localization, protein expression, and regulation
- 2004
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Ingår i: Am J Physiol Regul Integr Comp Physiol. - : American Physiological Society. - 0363-6119. ; 287:4
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Tidskriftsartikel (refereegranskat)abstract
- Transplacental transfer is the fetus' primary source of taurine, an essential amino acid during fetal life. In intrauterine growth restriction (IUGR), placental transport capacity of taurine is reduced and fetal taurine levels are decreased. We characterized the protein expression of the taurine transporter (TAUT) in human placenta using immunocytochemistry and Western blotting, tested the hypothesis that placental protein expression of TAUT is reduced in IUGR, and investigated TAUT regulation by measuring the Na(+)-dependent taurine uptake in primary villous fragments after 1 h of incubation with different effectors. TAUT was primarily localized in the syncytiotrophoblast microvillous plasma membrane (MVM). TAUT was detected as a single 70-kDa band, and MVM TAUT expression was unaltered in IUGR. The PKC activator PMA and the nitric oxide (NO) donor 3-morpholinosydnonimine decreased TAUT activity (P < 0.05, n = 7-15). However, none of the tested hormones, e.g., leptin and growth hormone, altered TAUT activity significantly. PKC activity measured in MVM from control and IUGR placentas was not different. In conclusion, syncytiotrophoblast TAUT is strongly polarized to the maternal-facing plasma membrane. MVM TAUT expression is unaltered in IUGR, suggesting that the reduced MVM taurine transport in IUGR is due to changes in transporter activity. NO release downregulates placental TAUT activity, and it has previously been shown that IUGR is associated with increased fetoplacental NO levels. NO may therefore play an important role in downregulating MVM TAUT activity in IUGR.
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| 12. |
- Roos, Sara, 1979, et al.
(författare)
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Mammalian target of rapamycin in the human placenta regulates leucine transport and is down-regulated in restricted fetal growth.
- 2007
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Ingår i: The Journal of physiology. - : Wiley. - 0022-3751. ; 582:Pt 1, s. 449-59
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Tidskriftsartikel (refereegranskat)abstract
- Pathological fetal growth is associated with perinatal morbidity and the development of diabetes and cardiovascular disease later in life. Placental nutrient transport is a primary determinant of fetal growth. In human intrauterine growth restriction (IUGR) the activity of key placental amino acid transporters, such as systems A and L, is decreased. However the mechanisms regulating placental nutrient transporters are poorly understood. We tested the hypothesis that the mammalian target of rapamycin (mTOR) signalling pathway regulates amino acid transport in the human placenta and that the activity of the placental mTOR pathway is reduced in IUGR. Using immunohistochemistry and culture of trophoblast cells, we show for the first time that the mTOR protein is expressed in the transporting epithelium of the human placenta. We further demonstrate that placental mTOR regulates activity of the l-amino acid transporter, but not system A or taurine transporters, by determining the mediated uptake of isotope-labelled leucine, methylaminoisobutyric acid and taurine in primary villous fragments after inhibition of mTOR using rapamycin. The protein expression of placental phospho-S6K1 (Thr-389), a measure of the activity of the mTOR signalling pathway, was markedly reduced in placentas obtained from pregnancies complicated by IUGR. These data identify mTOR as an important regulator of placental amino acid transport, and provide a mechanism for the changes in placental leucine transport in IUGR previously demonstrated in humans. We propose that mTOR functions as a placental nutrient sensor, matching fetal growth with maternal nutrient availability by regulating placental nutrient transport.
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| 13. |
- Roos, Sara, 1979, et al.
(författare)
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Mitochondrial complex IV deficiency caused by a novel frameshift variant in MT-CO2 associated with myopathy and perturbed acylcarnitine profile
- 2019
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Ingår i: European Journal of Human Genetics. - : Springer Science and Business Media LLC. - 1018-4813 .- 1476-5438. ; 27:2, s. 331-335
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Tidskriftsartikel (refereegranskat)abstract
- Mitochondrial myopathies are a heterogeneous group of disorders associated with a wide range of clinical phenotypes. We present a 16-year-old girl with a history of exercise intolerance since childhood. Acylcarnitine species suggestive of multiple acyl-CoA dehydrogenase deficiency were found in serum, however genetic analysis did not reveal variants in genes associated with this disorder. Biochemical analyses of skeletal muscle mitochondria revealed an isolated and extremely low activity of cytochrome c oxidase (COX). This finding was confirmed by enzyme histochemistry, which demonstrated an almost complete absence of fibers with normal COX activity. Whole-exome sequencing revealed a single base-pair deletion (m.8088delT) in MT-CO2, which encodes subunit 2 of COX, resulting in a premature stop codon. Restriction fragment length polymorphism-analysis confirmed mtDNA heteroplasmy with high mutant load in skeletal muscle, the only clinically affected tissue, but low levels in other investigated tissues. Single muscle fiber analysis showed segregation of the mutant genotype with respiratory chain dysfunction. Immuno-histochemical studies indicated that the truncating variant in COX2 has an inhibitory effect on the assembly of the COX holoenzyme.
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| 14. |
- Roos, Sara, 1979, et al.
(författare)
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Mitochondrial DNA depletion in single fibers in a patient with novel TK2 mutations
- 2014
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Ingår i: Neuromuscular Disorders. - : Elsevier BV. - 0960-8966 .- 1873-2364. ; 24:8, s. 713-720
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Tidskriftsartikel (refereegranskat)abstract
- The mitochondrial DNA (mtDNA) depletion syndrome is a genetically heterogeneous group of diseases caused by nuclear gene mutations and secondary reduction in mtDNA copy number. We describe a patient with progressive muscle weakness and increased creatine kinase and lactate levels. Muscle weakness was first noted at age 1.5 years and he died of respiratory failure and bronchopneumonia at age 3.5 years. The muscle biopsy showed dystrophic features with ragged red fibers and numerous cytochrome c oxidase (COX)-negative fibers. qPCR analysis demonstrated depletion of mtDNA and sequence analysis of the mitochondrial thymidine kinase 2 (TK2) gene revealed two novel heterozygous variants, c.332C > T, p.(T111I) and c.156 + 5G > C. Quantitative analysis of mtDNA in single muscle fibers demonstrated that COX-deficient fibers showed more pronounced depletion of mtDNA when compared with fibers with residual COX activity (P < 0.01, n = 25). There was no evidence of manifestations from other organs than skeletal muscle although there was an apparent reduction of mtDNA copy number also in liver. The patient showed a pronounced, albeit transient, improvement in muscle strength after onset of treatment with coenzyme Q10, asparaginase, and increased energy intake, suggesting that nutritional modulation may be a therapeutic option in myopathic mtDNA depletion syndrome. (C) 2014 Elsevier B.V. All rights reserved.
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| 15. |
- Roos, Sara, 1979, et al.
(författare)
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Placental mTOR links maternal nutrient availability to fetal growth.
- 2009
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Ingår i: Biochemical Society transactions. - 1470-8752. ; 37:Pt 1, s. 295-8
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Tidskriftsartikel (refereegranskat)abstract
- The mTOR (mammalian target of rapamycin) signalling pathway functions as a nutrient sensor, both in individual cells and, more globally, in organs such as the fat body in Drosophila and the hypothalamus in the rat. The activity of placental amino acid transporters is decreased in IUGR (intrauterine growth restriction), and recent experimental evidence suggests that these changes contribute directly to the restricted fetal growth. We have shown that mTOR regulates the activity of the placental L-type amino acid transporter system and that placental mTOR activity is decreased in IUGR. The present review summarizes the emerging evidence implicating placental mTOR signalling as a key mechanism linking maternal nutrient and growth factor concentrations to amino acid transport in the human placenta. Since fetal growth is critically dependent on placental nutrient transport, placental mTOR signalling plays an important role in the regulation of fetal growth.
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| 16. |
- Roos, Sara, 1979, et al.
(författare)
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Regulation of amino acid transporters by glucose and growth factors in cultured primary trophoblast cells is mediated by mTOR signaling
- 2009
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Ingår i: American Journal of Physiology - Cell Physiology. - : American Physiological Society. - 0363-6143 .- 1522-1563. ; 298, s. C723-C731
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Tidskriftsartikel (refereegranskat)abstract
- Inhibition of mammalian target of rapamycin (mTOR) signaling in cultured human primary trophoblast cells reduces the activity of key placental amino acid transporters. However, the upstream regulators of placental mTOR are unknown. We hypothesized that glucose, insulin, and IGF-I regulate placental amino acid transporters by inducing changes in mTOR signaling. Primary human trophoblast cells were cultured for 24 h with media containing various glucose concentrations, insulin, or IGF-I, with or without the mTOR inhibitor rapamycin, and, subsequently, the activity of system A, system L, and taurine (TAUT) transporters was measured. Glucose deprivation (0.5 mM glucose) did not significantly affect Thr172-AMP-activated protein kinase phosphorylation or REDD1 expression but decreased S6 kinase 1 phosphorylation at Thr389. The activity of system L decreased in a dose-dependent manner in response to decreasing glucose concentrations. This effect was abolished in the presence of rapamycin. Glucose deprivation had two opposing effects on system A activity: 1) an “adaptive” upregulation mediated by an mTOR-independent mechanism and 2) downregulation by an mTOR-dependent mechanism. TAUT activity was increased after incubating cells with glucose-deprived media, and this effect was largely independent of mTOR signaling. Insulin and IGF-I increased system A activity and insulin stimulated system L activity, effects that were abolished by rapamycin. We conclude that the mTOR pathway represents an important intracellular regulatory link between nutrient and growth factor concentrations and amino acid transport in the human placenta.intrauterine growth restriction (IUGR) and accelerated fetal growth represent two important clinical conditions that occur in 15% of all pregnancies (1, 2). Aberrant fetal growth is associated with an increased risk of perinatal morbidity (7) as well as metabolic abnormalities in adult life, such as obesity, type 2 diabetes, and cardiovascular disease (6, 12, 46). The most important determinant of fetal growth is nutrient availability, which is highly dependent on placental transport capacity. The mechanisms underlying altered fetal growth remain to be established, but accumulating evidence implicates changes in the activity of specific placental amino acid transporters as a critical factor contributing to abnormal fetal growth (27, 54). Experimental evidence supports the hypothesis that changes in placental nutrient transporter activity are a cause of rather than a response to altered fetal growth. For example, in pregnant rats subjected to protein malnutrition, it is likely that downregulation of the placental system A amino acid transporter directly contributes to the development of IUGR (26).In IUGR, fetuses may be hypoglycemic (15) and have reduced circulating levels of insulin (43) and IGF-I (4, 34). The maternal levels of glucose (15) and IGF-I (40, 41) may also be reduced in this condition. The placenta of the IUGR fetus could therefore be exposed to decreased levels of glucose, hormones, and growth factors. Both insulin and IGF-I stimulate placental system A activity (24, 30, 31). These results suggest that extracellular cues regulate placental nutrient transporters and, as a consequence, fetal nutrient supply, but the cellular mechanisms remain to be fully established.The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that is regulated by a multitude of intracellular and extracellular signals. For example, mTOR is activated by growth factors and nutrient levels, such as amino acids (59), and inhibited by numerous stress conditions, such as cellular energy depletion (13, 17). Glucose may also regulate mTOR signaling through energy production in the form of ATP (13, 17). The AMP-activated protein kinase (AMPK) is regulated by the AMP-to-ATP ratio, which rises under nutrient deprivation and activates AMPK (10). Activated AMPK can in turn phosphorylate tuberous sclerosis complex 2 (TSC2), leading to mTOR inactivation (23). AMPK is phosphorylated and activated by LKB1 (52), and it has been shown that phosphorylation of LKB1 at Ser428 is essential for AMPK activation by metformin, and the authors speculate that LKB1-Ser428 phosphorylation may be a common pathway required for AMPK activation (60). There might also be additional, AMPK-independent, pathways involved in energy depletion. A recent report has shown that REDD1 (regulated in development and DNA damage responses 1) in mouse embryonic fibroblasts is induced by chronic energy depletion, and this in turn leads to inactivation of mTOR complex 1 (mTORC1) measured as phosphorylation of S6 kinase 1 (S6K1) at Thr389, independent of AMPK (55).Insulin and IGF-I activate the tyrosine kinase activity of its receptors to phosphorylate the insulin receptor substrate 1, which in turn activates phosphatidylinositol 3-kinase (PI3K) to generate PI(3,4,5)P3. Phosphatidylinositol 3,4,5-trisphosphate (PIP3) binding to Akt leads to the translocation of Akt to the plasma membrane, where it is phosphorylated and activated. The activation of Akt positively modulates mTORC1 function, by phosphorylating, and inhibiting, TSC2 (reviewed in Ref. 59).We have previously shown that inhibition of mTOR reduces the activity of placental system L, system A, and the taurine transporter (TAUT) (50). Since the activity of these amino acid transporter systems is downregulated in the placenta in association to IUGR (14, 19, 28, 37, 45) and placental mTOR activity has been reported to be decreased in IUGR (49, 62), it is possible that mTOR signaling plays an important role in regulating placental amino acid transporters in vivo. However, the upstream regulators of placental mTOR are unknown. We hypothesized that glucose, insulin, and IGF-I regulate placental amino acid transporter activity by inducing changes in mTOR signaling. To test this hypothesis, human primary trophoblast cells were incubated with media containing various concentrations of glucose, insulin, or IGF-I in the presence or absence of the specific mTOR inhibitor rapamycin. Subsequently, the activity of system L, system A, and the taurine transporter was measured. To investigate whether the AMPK pathway and/or REDD1 is activated in glucose-deprived primary trophoblasts, the protein expression of phosphorylated (P)-Thr172-AMPKα, total AMPK, P-Ser428-LKB1, and REDD1 in control and glucose-deprived cells was also studied.
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| 17. |
- Roos, Sara, 1979, et al.
(författare)
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Regulation of placental amino acid transporter activity by mammalian target of rapamycin.
- 2009
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Ingår i: American journal of physiology. Cell physiology. - : American Physiological Society. - 0363-6143 .- 1522-1563. ; 296:1
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Tidskriftsartikel (refereegranskat)abstract
- The activity of placental amino acid transporters is decreased in intrauterine growth restriction (IUGR), but the underlying regulatory mechanisms have not been established. Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has been shown to decrease the activity of the system L amino acid transporter in human placental villous fragments, and placental mTOR activity is decreased in IUGR. In the present study, we used cultured primary trophoblast cells to study mTOR regulation of placental amino acid transporters in more detail and to test the hypothesis that mTOR alters amino acid transport activity by changes in transporter expression. Inhibition of mTOR by rapamycin significantly reduced the activity of system A (-17%), system L (-28%), and taurine (-40%) amino acid transporters. mRNA expression of isoforms of the three amino acid transporter systems in response to mTOR inhibition was measured using quantitative real-time PCR. mRNA expression of l-type amino acid transporter 1 (LAT1; a system L isoform) and taurine transporter was reduced by 13% and 50%, respectively; however, mTOR inhibition did not alter the mRNA expression of system A isoforms (sodium-coupled neutral amino acid transporter-1, -2, and -4), LAT2, or 4F2hc. Rapamycin treatment did not significantly affect the protein expression of any of the transporter isoforms. We conclude that mTOR signaling regulates the activity of key placental amino acid transporters and that this effect is not due to a decrease in total protein expression. These data suggest that mTOR regulates placental amino acid transporters by posttranslational modifications or by affecting transporter translocation to the plasma membrane.
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| 18. |
- Roos, Sara, 1979, et al.
(författare)
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Subnormal levels of POLgA cause inefficient initiation of light-strand DNA synthesis and lead to mitochondrial DNA deletions and progressive external ophthalmoplegia
- 2013
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 22:12, s. 2411-2422
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Tidskriftsartikel (refereegranskat)abstract
- The POLG1 gene encodes the catalytic subunit of mitochondrial DNA (mtDNA) polymerase γ (POLγ). We here describe a sibling pair with adult-onset progressive external ophthalmoplegia, cognitive impairment and mitochondrial myopathy characterized by DNA depletion and multiple mtDNA deletions. The phenotype is due to compound heterozygous POLG1 mutations, T914P and the intron mutation c.3104 + 3A > T. The mutant genes produce POLγ isoforms with heterozygous phenotypes that fail to synthesize longer DNA products in vitro. However, exon skipping in the c.3104 + 3A > T mutant is not complete, and the presence of low levels of wild-type POLγ explains patient survival. To better understand the underlying pathogenic mechanisms, we characterized the effects of POLγ depletion in vitro and found that leading-strand DNA synthesis is relatively undisturbed. In contrast, initiation of lagging-strand DNA synthesis is ineffective at lower POLγ concentrations that uncouples leading strand from lagging-strand DNA synthesis. In vivo, this effect leads to prolonged exposure of the heavy strand in its single-stranded conformation that in turn can cause the mtDNA deletions observed in our patients. Our findings, thus, suggest a molecular mechanism explaining how POLγ mutations can cause mtDNA deletions in vivo.
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| 19. |
- Roos, Sara, 1979, et al.
(författare)
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The human placental taurine transporter in uncomplicated and IUGR pregnancies: cellular localization, protein expression, and regulation
- 2004
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Ingår i: Placenta. - 0143-4004. ; 25:8-9
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Konferensbidrag (refereegranskat)abstract
- Transplacental transfer is the fetus’ primary source of taurine, an essential amino acid during fetal life. In intrauterine growth restriction (IUGR) placental transport capacity of taurine is reduced and fetal taurine levels are decreased. Methods: Immunocytochemistry was used to study cellular localization of the taurine transporter (TAUT), protein expression was studied by Western blotting, and TAUT regulation by measuring the sodium-dependent taurine uptake in primary villous fragments after 1 h incubation with different effectors. Results: TAUT was primarily detected in the syncytiotrophoblast microvillous plasma membrane (MVM). In Western blot analysis TAUT was detected as a single 70kDa band and MVM TAUT expression was unaltered in IUGR (n=8). Phorbol 12-myristate 13-acetate, a stimulator of protein kinase C, and the NO donor 3-morpholinosydnonimine decreased TAUT activity (n= 7-15, p<0.05). However, none of the tested hormones, such as leptin, cortisol, and insulin, altered TAUT activity significantly (n=6-15). PKC activity measured in MVM isolated from AGA and IUGR placentas was found to be similar (n=8). Conclusions: TAUT in the transporting epithelium of the human placenta is strongly polarized to the maternal-facing plasma membrane. MVM TAUT expression is unaltered in IUGR suggesting that the reduction in MVM taurine transport in association to IUGR is due to changes in transporter activity. PKC-mediated phosphorylation and NO release downregulate TAUT activity. MVM PKC-activity is unaltered in IUGR, but NO levels have previously been shown to be higher in IUGR, suggesting a possible mechanism for the reduced taurine uptake across MVM in IUGR.
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| 20. |
- Roos, Sara, 1979
(författare)
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The Role of Mammalian Target of Rapamycin in the Regulation of Amino Acid Transporters in the Human Placenta
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abnormal fetal growth, which is associated with both perinatal morbidity as well as metabolic diseases in adulthood, is an important clinical problem affecting as many as 15% of all pregnancies. However, to this date, there is no specific treatment of this condition. Fetal growth is intimately linked to the nutrient transport functions of the placenta and placental amino acid transporter activity is known to be altered in cases of abnormal fetal growth. Therefore, detailed information on the mechanisms regulating placental amino acid transporters will increase our understanding of how abnormal fetal growth develops and may provide new targets for therapeutic intervention. The focus of this study was to identify factors, such as hormones and growth factors, regulating three key amino acid transporters in the human placenta; system L, system A, and system β. The central hypothesis was that mammalian target of rapamycin (mTOR) signaling regulates placental amino acid transporters in the human placenta in response to nutrient availability and growth factors such as insulin and IGF-I. To test this hypothesis, we have used cultured primary trophoblast cells, primary villous fragments, and homogenates, all from the human placenta, to study the regulation of amino acid transport. We show that the mTOR signaling pathway constitutes an important positive regulator of the placental amino acid transporters system A, system L, and the taurine transporter (system β). Furthermore, we demonstrate that these amino acid transporters are regulated by nutrients, such as glucose, and growth factors, such as insulin and IGF-I, in an mTOR dependent manner. Placental mTOR activity was found to be decreased in intrauterine growth restriction (IUGR), which may explain the down-regulation of placental amino acid transporters in this pregnancy complication. We propose a model in which placental mTOR functions as a nutrient sensor linking maternal nutrient and growth factor concentrations to amino acid transport in the placenta. Since fetal growth is critically dependent on placental nutrient transport, these data suggest that placental mTOR signaling plays an important role in the regulation of fetal growth. The regulation of amino acid transport is important not only in the placenta. Our results were obtained in primary human tissue fragments and cells from the placenta, however, we believe that findings in this study are also relevant for other human tissues such as the skeletal muscle and liver. Furthermore, the growth of many tumor cells is dependent on a high expression of amino acid transporters and detailed information on the mechanisms of regulation of these transporters may facilitate the development of new interventions.
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