| 1. |
- Dickson, Elna, et al.
(författare)
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Altered Adipocyte Cell Size Distribution Prior to Weight Loss in the R6/2 Model of Huntington's Disease
- 2023
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Ingår i: Journal of Huntington's disease. - 1879-6397. ; 12:3, s. 253-266
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Metabolic alterations contribute to disease onset and prognosis of Huntington's disease (HD). Weight loss in the R6/2 mouse model of HD is a consistent feature, with onset in mid-to-late stage of disease.OBJECTIVE: In the present study, we aimed to investigate molecular and functional changes in white adipose tissue (WAT) that occur at weight loss in R6/2 mice. We further elaborated on the effect of leptin-deficiency and early obesity in R6/2 mice.METHODS: We performed analyses at 12 weeks of age; a time point that coincides with the start of weight loss in our R6/2 mouse colony. Gonadal (visceral) and inguinal (subcutaneous) WAT depot weights were monitored, as well as adipocyte size distribution. Response to isoprenaline-stimulated glycerol release and insulin-stimulated glucose uptake in adipocytes from gonadal WAT was assessed.RESULTS: In R6/2 mice, WAT depot weights were comparable to wildtype (WT) mice, and the response to insulin and isoprenaline in gonadal adipocytes was unaltered. Leptin-deficient R6/2 mice exhibited distinct changes compared to leptin-deficient WT mice. At 12 weeks, female leptin-deficient R6/2 mice had reduced body weight accompanied by an increased proportion of smaller adipocytes, while in contrast; male mice displayed a shift towards larger adipocyte sizes without a significant body weight reduction at this timepoint.CONCLUSIONS: We here show that there are early sex-specific changes in adipocyte cell size distribution in WAT of R6/2 mice and leptin-deficient R6/2 mice.
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| 2. |
- Fryklund, Claes
(författare)
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Adipocyte size and function in the epididymal and inguinal fat depots
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nearly 60% of the worlds adult population is projected to be overweight or obese by 2030. The prevalence of obesity- related diseases, such as type 2 diabetes (T2D), has increased markedly in the past decades. The adipose tissue plays an important role in disease progression of T2D. Adipocyte insulin sensitivity, adipose tissue’s ability to expand, and accumulation of subcutaneous rather than visceral fat, are all important factors for adipose tissue function and systemic metabolic health.This thesis aims to broaden the understanding of adipose tissue function, focusing on the importance of adipocyte cell-size and differences between visceral and subcutaneous adipocytes. This knowledge may in the future contribute to novel treatments that focus on improving function of specific fat depots.Our first project (Paper I) examines the importance of EHD2, a caveolae-associated protein, and its influence on different fat depots by using knockout (Ehd2-/-) mice. Ehd2-/- mice display impaired expansion of epididymal fat, most likely caused by weakened hyperplastic growth, while the inguinal adipocytes exhibit impaired lipolytic response. The results indicate that EHD2 is required for healthy fat expansion since both impaired lipolysis and reduced hyperplastic growth are associated with dysfunctional adipose tissue.In Paper II, we examine the effect of the anti-diabetic drug, rosiglitazone, on hypertrophic adipocytes, and suggest a new mechanism of action for improving insulin-sensitivity in adipocytes. We propose that remodeling of the extracellular matrix (ECM), results in reduced stress-induced intracellular signaling, reduced filamentous (F)-actin and improved insulin-stimulated glucose uptake. The improvement in glucose uptake from rosiglitazone-treated mice are greater in epididymal adipocytes compared to inguinal, which is also reflected in larger changes in ECM expression, intracellular stress signaling and level of F-actin.The last project (Paper III) examines the plasticity of adipose tissue, focusing on cell-size and actin dynamics during weight gain and weight loss. We examine differences between the inguinal and epididymal depots using temporal resolution and correlate the findings to changes in systemic insulin sensitivity. Our data suggest that there are fat depot-specific differences in cell-size plasticity during weight gain, but not during weight loss. Epididymal adipocytes expand in size early during weight gain (after 4 weeks) while inguinal adipocytes expand at a later timepoint (after 12 weeks). During weight loss, both fat depots display intact plasticity, regarding cell-size, weight, and level of F- actin, for short interventions (4 and 8 weeks) but not following prolonged overfeeding (12 weeks).The inguinal depot, in comparison to the epididymal depot, displays stronger correlation between insulin sensitivity and number of hypertrophic adipocytes, suggesting that hypertrophic inguinal adipocytes may contribute to the progression of insulin resistance in mice.
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| 3. |
- Fryklund, Claes, et al.
(författare)
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Adipocyte traits limiting cellular insulin responsiveness and glucose transport
- 2023
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Ingår i: American Journal of Physiology - Endocrinology and Metabolism. - 1522-1555. ; 325:6, s. 682-687
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Tidskriftsartikel (refereegranskat)abstract
- Adipocyte dysfunction is a hallmark of systemic insulin resistance. Insulin-responsive glucose transporter 4 (GLUT4) is downregulated in the insulin resistant state, and cellular insulin responsiveness varies depending on fat-depot origin and degree of adipose expansion. Here, we have resolved factors limiting cellular insulin responsiveness, by examining adipocyte function and traits related to glucose transport at the cellular level. Subcutaneous (inguinal) and visceral (epididymal) adipocytes were isolated from C57BL/6J mice fed either chow or high-fat diet. Cell-size was determined using coulter counter method, glucose uptake and cytosolic volume were assessed using glucose-tracer assays. Total and GLUT4 protein content expression were determined by western blot. We found that basal glucose uptake per cell was preserved independent of diet or fat depot origin. Insulin-stimulated glucose uptake per cell was sustained in visceral adipocytes but decreased with adipose expansion in subcutaneous adipocytes. In parallel, the cytosolic space and total protein increased proportionally to total cellular volumetric expansion in visceral, but not subcutaneous, adipocytes, while GLUT4 content decreased exclusively in expanding subcutaneous adipocytes. Together, these data support the existence of distinct phenotypic adipocyte traits that could limit cellular insulin responsiveness. Potentially, these characteristics account for fat depot-specific differences related to glucose transport capacity.
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| 4. |
- Fryklund, Claes, et al.
(författare)
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EH Domain-Containing 2 Deficiency Restricts Adipose Tissue Expansion and Impairs Lipolysis in Primary Inguinal Adipocytes
- 2021
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Lipid uptake can be facilitated via caveolae, specific plasma membrane invaginations abundantly expressed in adipocytes. The dynamin-related protein EH domain-containing 2 (EHD2) stabilizes caveolae at the cell surface. Here, we have examined the importance of EHD2 for lipid handling using primary adipocytes isolated from EHD2 knockout (Ehd2−/−) C57BL6/N mice. Following high-fat diet (HFD) feeding, we found a clear impairment of epididymal, but not inguinal, adipose tissue expansion in Ehd2−/− compared with Ehd2+/+ (WT) mice. Cell size distribution analysis revealed that Ehd2−/− mice had a lower proportion of small adipocytes, and an accumulation of medium-sized adipocytes in both epididymal and inguinal adipose tissue. Further, PPARγ activity, FABP4 and caveolin-1 expression were decreased in adipocytes isolated from Ehd2−/− mice. Inguinal adipocytes isolated from Ehd2−/− mice displayed reduced lipolysis in response to beta adrenergic receptor agonist, which was associated with reduced phosphorylation of perilipin-1 and hormone sensitive lipase (HSL). This impairment could not be rescued using a cAMP analog, indicating that impaired lipolysis in Ehd2−/− primary adipocytes likely occurs at the level of, or downstream of, protein kinase A (PKA). Altogether, these findings pinpoint the importance of EHD2 for maintained intracellular lipid metabolism, and emphasize differences in mechanisms regulating lipid handling in various adipose-tissue depots.
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| 5. |
- Fryklund, Claes, et al.
(författare)
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Expansion of the Inguinal Adipose Tissue Depot Correlates With Systemic Insulin Resistance in C57BL/6J Mice
- 2022
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Ingår i: Frontiers in Cell and Developmental Biology. - : Frontiers Media S.A.. - 2296-634X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- To accommodate surplus energy, the adipose tissue expands by increasing adipocyte size (hypertrophy) and number (hyperplasia). The presence of hypertrophic adipocytes is a key characteristic of adipose tissue dysfunction. High-fat diet (HFD) fed C57BL/6J mice are a commonly used model to study obesity and obesity-related complications. In the present study, we have characterized adipose plasticity, at both the cellular and tissue level, by examining the temporal development of systemic insulin resistance and adiposity in response to HFD-feeding for 4, 8, and 12 weeks (4w, 8w, and 12w). Within the same time frame, we examined systemic metabolic flexibility and adipose plasticity when switching from HFD- to chow-diet during the last 2 weeks of diet intervention (referred to as the reverse (REV) group: 4wREV (2w HFD+2w chow), 8wREV (6w HFD+2w chow), 12wREV (10w HFD+2w chow)). In response to HFD-feeding over time, the 12w group had impaired systemic insulin sensitivity compared to both the 4w and 8w groups, accompanied by an increase in hypertrophic inguinal adipocytes and liver triglycerides. After reversing from HFD- to chow-feeding, most parameters were completely restored to chow control levels for 4wREV and 8wREV groups. In contrast, the 12wREV group had a significantly increased number of hypertrophic adipocytes, liver triglycerides accumulation, and impaired systemic insulin sensitivity compared to chow-fed mice. Further, image analysis at the single-cell level revealed a cell-size dependent organization of actin filaments for all feeding conditions. Indeed, the impaired adipocyte size plasticity in the 12wREV group was accompanied by increased actin filamentation and reduced insulin-stimulated glucose uptake compared with chow-fed mice. In summary, these results demonstrate that the C57BL/6J HFD-feeding model has a large capacity to restore adipocyte cell size and systemic insulin sensitivity, and that a metabolic tipping point occurs between 8 and 12w of HFD-feeding where this plasticity deteriorates. We believe these findings provide substantial understanding of C57BL/6J mice as an obesity model, and that an increased pool of hypertrophic ING adipocytes could contribute to aggravated insulin resistance.
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| 6. |
- Fryklund, Claes, et al.
(författare)
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Impaired glucose transport in inguinal adipocytes after short-term high-sucrose feeding in mice
- 2020
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Ingår i: Journal of Nutritional Biochemistry. - : Elsevier BV. - 0955-2863. ; 78
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Tidskriftsartikel (refereegranskat)abstract
- Diets enriched in sucrose severely impair metabolic regulation and are associated with obesity, insulin resistance and glucose intolerance. In the current study, we investigated the effect of 4 weeks high-sucrose diet (HSD) feeding in C57BL6/J mice, with specific focus on adipocyte function. Mice fed HSD had slightly increased adipose tissue mass but displayed similar hepatic triglycerides, glucose and insulin levels, and glucose clearance capacity as chow-fed mice. Interestingly, we found adipose depot-specific differences, where both the non- and insulin-stimulated glucose transports were markedly impaired in primary adipocytes isolated from the inguinal fat depot from HSD-fed mice. This was accompanied by decreased protein levels of both GLUT4 and AS160. A similar but much less pronounced trend was observed in the retroperitoneal depot. In contrast, both GLUT4 expression and insulin-stimulated glucose uptake were preserved in adipocytes isolated from epididymal adipose tissue with HSD. Further, we found a slight shift in cell size distribution towards larger cells with HSD and a significant decrease of ACC and PGC-1α expression in the inguinal adipose tissue depot. Moreover, fructose alone was sufficient to decrease GLUT4 expression in cultured, mature adipocytes. Altogether, we demonstrate that short-term HSD feeding has deleterious impact on insulin response and glucose transport in the inguinal adipose tissue depot, specifically. These changes occur before the onset of systemic glucose dysmetabolism and therefore could provide a mechanistic link to overall impaired energy metabolism reported after prolonged HSD feeding, alone or in combination with HFD.
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| 7. |
- Fryklund, Claes, et al.
(författare)
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Rosiglitazone treatment enhances intracellular actin dynamics and glucose transport in hypertrophic adipocytes
- 2022
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Ingår i: Life Sciences. - : Elsevier BV. - 0024-3205. ; 299
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To accommodate surplus energy, adipose tissue expands by increasing both adipose cell size (hypertrophy) and cell number (hyperplasia). Enlarged, hypertrophic adipocytes are known to have reduced insulin response and impaired glucose transport, which negatively influence whole-body glucose homeostasis. Rosiglitazone is a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, known to stimulate hyperplasia and to efficiently improve insulin sensitivity. Still, a limited amount of research has investigated the effects of rosiglitazone in mature, hypertrophic adipocytes. Therefore, the objective of this study was to examine rosiglitazone's effect on insulin-stimulated glucose uptake in hypertrophic adipocytes. Main methods: C57BL/6J male mice were subjected to 2 weeks of high-fat diet (HFD) followed by 1 week of HFD combined with daily administration of rosiglitazone (10 mg/kg). Adipose cell-size distribution and gene expression were analysed in intact adipose tissue, and glucose uptake, insulin response, and protein expression were examined using primary adipocytes isolated from epididymal and inguinal adipose tissue. Key findings: HFD-feeding induced an accumulation of hypertrophic adipocytes, which was not affected by rosiglitazone-treatment. Still, rosiglitazone efficiently improved insulin-stimulated glucose transport without restoring insulin signaling or GLUT4 expression in similar-sized adipocytes. This improvement occurred concurrently with extracellular matrix remodelling and restored intracellular levels of targets involved in actin turnover. Significance: These results demonstrate that rosiglitazone improves glucose transport in hypertrophic adipocytes, and highlights the importance of the cytoskeleton and extracellular matrix as potential therapeutic targets.
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| 8. |
- Hansson, Björn, et al.
(författare)
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A hypothesis for insulin resistance in primary human adipocytes involving MRTF-A and suppression of PPARγ
- 2020
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 0006-291X. ; 533:1, s. 64-69
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is the main risk factor behind insulin resistance and type 2 diabetes. Still, the mechanism behind adipocyte dysfunction is not yet resolved. Recently, we reported that rapid actin remodeling correlates with adipose cell size changes after short-term overfeeding. Therefore, we hypothesized that the actin-driven myocardin-related transcription factor (MRTF-A) contributes to impaired mature adipocyte function. Primary human adipocytes were subjected to adenoviral overexpression of MRTF-A or MRTF-B, followed by Western blot analysis and tracer glucose uptake assay. Further, we assessed cell size distribution, insulin response, MRTF-A localization, actin organization and degree of polymerization in adipocytes isolated from Ob/Ob mice. Overexpression of MRTF-A, but not MRTF-B, markedly suppressed PPARγ expression. Further, MRTF-A expression resulted in decreased IRS-1 level, shifted phosphorylation of Akt (pS473/pT308), IRS-1 (pS302) and AS160 (pT642), and lowered insulin-stimulated glucose uptake. Hypertrophic adipocytes from Ob/Ob mice displayed an increased proportion of polymerized actin, and increased nuclear translocation of MRTF-A compared with control (Ob/+). Similar with human adipocytes overexpressing MRTF-A, adipocytes isolated from Ob/Ob mice had reduced expression of IRS-1 and PPARγ, as well as impaired insulin response. Together, these data demonstrate that MRTF-A negatively influences insulin sensitivity and the expression of key targets in fully mature human adipocytes. This suggests that MRTF-A is poised to exert a transcriptional response in hypertrophic adipocytes, contributing to adipocyte dysfunction and insulin resistance.
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| 9. |
- Hansson, Björn, et al.
(författare)
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Adipose cell size changes are associated with a drastic actin remodeling
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Adipose tissue plays a major role in regulating whole-body insulin sensitivity and energy metabolism. To accommodate surplus energy, the tissue rapidly expands by increasing adipose cell size (hypertrophy) and cell number (hyperplasia). Previous studies have shown that enlarged, hypertrophic adipocytes are less responsive to insulin, and that adipocyte size could serve as a predictor for the development of type 2 diabetes. In the present study, we demonstrate that changes in adipocyte size correlate with a drastic remodeling of the actin cytoskeleton. Expansion of primary adipocytes following 2 weeks of high-fat diet (HFD)-feeding in C57BL6/J mice was associated with a drastic increase in filamentous (F)-actin as assessed by fluorescence microscopy, increased Rho-kinase activity, and changed expression of actin-regulating proteins, favoring actin polymerization. At the same time, increased cell size was associated with impaired insulin response, while the interaction between the cytoskeletal scaffolding protein IQGAP1 and insulin receptor substrate (IRS)-1 remained intact. Reversed feeding from HFD to chow restored cell size, insulin response, expression of actin-regulatory proteins and decreased the amount of F-actin filaments. Together, we report a drastic cytoskeletal remodeling during adipocyte expansion, a process which could contribute to deteriorating adipocyte function.
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| 10. |
- Hansson, Björn, et al.
(författare)
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Serotonin (5-HT) and 5-HT2A receptor agonists suppress lipolysis in primary rat adipose cells
- 2016
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 0006-291X. ; 474:2, s. 357-363
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Tidskriftsartikel (refereegranskat)abstract
- Serotonin (5-HT) is a biogenic monoamine that functions both as a neurotransmitter and a circulating hormone. Recently, the metabolic effects of 5-HT have gained interest and peripheral 5-HT has been proposed to influence lipid metabolism in various ways. Here, we investigated the metabolic effects of 5-HT in isolated, primary rat adipose cells. Incubation with 5-HT suppressed β-adrenergically stimulated glycerol release and decreased phosphorylation of protein kinase A (PKA)-dependent substrates, hormone sensitive lipase (Ser563) and perilipin (Ser522). The inhibitory effect of 5-HT on lipolysis enhanced the anti-lipolytic effect of insulin, but sustained in the presence of phosphodiesterase inhibitors, OPC3911 and isobuthylmethylxanthine (IBMX). The relative expression of 5-HT1A, -2B and -4 receptor class family were significantly higher in adipose tissue compared to adipose cells, whereas 5-HT1D, -2A and -7 were highly expressed in isolated adipose cells. Similar to 5-HT, 5-HT2 receptor agonists reduced lipolysis while 5-HT1 receptor agonists rather decreased non-stimulated and insulin-stimulated glucose uptake. Together, these data provide evidence of a direct effect of 5-HT on adipose cells, where 5-HT suppresses lipolysis and glucose uptake, which could contribute to altered systemic lipid- and glucose metabolism.
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