| 1. |
- Arner, Anders, et al.
(författare)
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Intracellular calcium in hypertrophic smooth muscle from rat urinary bladder
- 2007
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Ingår i: Scandinavian Journal of Urology and Nephrology. - : Informa UK Limited. - 0036-5599 .- 1651-2065. ; 41:4, s. 270-277
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To explore whether infravesical outlet obstruction is associated with alterations in calcium activation of detrusor smooth muscle. Material and methods. Outlet obstruction was created by partial ligature of the urethra in female rats. Western blotting was performed using an antibody against the cytoplasmatic region of the alpha(1c) subunit of the L- type Ca2(+) channel. Intracellular calcium was measured using Fura-2 in detrusors that had been obstructed for 10 days and activated by high K+ concentrations at different extracellular Ca2(+) concentrations. The rate of force development after rapid opening of L- type Ca2(+) channels was measured in contractions initiated by flash photolysis of nifedipine in Ca2(+) containing depolarizing solution. Results. Bladder weight increased from 6293 to 254943 mg after 10 days of obstruction. Expression of the alpha(1c) subunit increased after 3 days and continued to increase until it was about fourfold greater after 10 days; however, it had not increased further at 6 weeks. This change was reversible after removal of obstruction. Activation with K+ produced a stable force at different extracellular Ca2(+) concentrations, with no difference in response between controls and rats that had been obstructed for 10 days. Intracellular Ca2(+) concentrations were lower in the obstructed group, showing that the calcium sensitivity of the contraction force had increased. The delay between the opening of L- type channels and the onset of contraction was longer in obstructed detrusors. Conclusions. Growth of detrusor muscle following obstruction is accompanied by attenuated calcium transients following activation, despite upregulation of L- type Ca2(+) channels. The Ca2(+) sensitivity of contraction was increased in obstructed detrusors. We suggest that the decreased surface: volume ratio in hypertrophic smooth muscle cells is partly involved in the lowered Ca2(+) transients. The increases in L- type calcium channels and in calcium sensitivity may be compensatory mechanisms.
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| 2. |
- Scott, Rolf Sjuve, et al.
(författare)
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The role of desmin in active force transmission and maintenance of structure during growth of urinary bladder.
- 2008
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Ingår i: American Journal of Physiology: Cell Physiology. - : American Physiological Society. - 1522-1563 .- 0363-6143. ; 295:2, s. 324-331
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Tidskriftsartikel (refereegranskat)abstract
- The role of the intermediate filament protein desmin in hypertrophy of smooth muscle was examined in desmin deficient mice (Des -/-). A partial obstruction of the urethra was created and after 9-19 days bladder weight increased about 3-fold in both Des -/- and wild type (Des +/+) animals. Bladder growth was associated with synthesis of actin and myosin. In the hypertrophic Des +/+ bladder the relative content of desmin increased. In Des -/- mice desmin was absent. No alterations in the amount of vimentin were observed. Although Des -/- obstructed bladders were capable of growth they had structural changes with partial disruption of the wall. Des-/- bladders had slightly lower passive stress and significantly lower active stress compared to Des+/+. Des-/- preparations had lower shortening velocity. During hypertrophy these structural and mechanical alterations in the Des-/- urinary bladder became more pronounced. In conclusion, desmin in the bladder smooth muscle is not needed for growth but has a role in active force transmission and maintenance of wall structure. Key words: smooth muscle, intermediate filaments, desmin, transgenic.
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| 3. |
- Swärd, Karl, et al.
(författare)
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Identification of the intermediate filament protein synemin/SYNM as a target of myocardin family coactivators
- 2019
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Ingår i: American Journal of Physiology - Cell Physiology. - : American Physiological Society. - 0363-6143 .- 1522-1563. ; 317:6, s. 1128-1142
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Tidskriftsartikel (refereegranskat)abstract
- Myocardin (MYOCD) is a critical regulator of smooth muscle cell (SMC) differentiation, but its transcriptional targets remain to be exhaustively characterized, especially at the protein level. Here we leveraged human RNA and protein expression data to identify novel potential MYOCD targets. Using correlation analyses we found several targets that we could confirm at the protein level, including SORBS1, SLMAP, SYNM, and MCAM. We focused on SYNM, which encodes the intermediate filament protein synemin. SYNM rivalled smooth muscle myosin (MYH11) for SMC specificity and was controlled at the mRNA and protein levels by all myocardin-related transcription factors (MRTFs: MYOCD, MRTF-A/MKL1, and MRTF-B/MKL2). MRTF activity is regulated by the ratio of filamentous to globular actin, and SYNM was accordingly reduced by interventions that depolymerize actin, such as latrunculin treatment and overexpression of constitutively active cofilin. Many MRTF target genes depend on serum response factor (SRF), but SYNM lacked SRF-binding motifs in its proximal promoter, which was not directly regulated by MYOCD. Furthermore, SYNM resisted SRF silencing, yet the time course of induction closely paralleled that of the SRF-dependent target gene ACTA2. SYNM was repressed by the ternary complex factor (TCF) FLI1 and was increased in mouse embryonic fibroblasts lacking three classical TCFs (ELK1, ELK3, and ELK4). Imaging showed colocalization of SYNM with the intermediate filament proteins desmin and vimentin, and MRTF-A/MKL1 increased SYNM-containing intermediate filaments in SMCs. These studies identify SYNM as a novel SRF-independent target of myocardin that is abundantly expressed in all SMCs.
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| 4. |
- Zhu, Baoyi, et al.
(författare)
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Antagonistic relationship between the unfolded protein response and myocardin-driven transcription in smooth muscle
- 2020
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Ingår i: Journal of Cellular Physiology. - : Wiley. - 0021-9541 .- 1097-4652. ; 235:10, s. 7370-7382
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Tidskriftsartikel (refereegranskat)abstract
- Smooth muscle cells (SMCs) are characterized by a high degree of phenotypic plasticity. Contractile differentiation is governed by myocardin-related transcription factors (MRTFs), in particular myocardin (MYOCD), and when their drive is lost, the cells become proliferative and synthetic with an expanded endoplasmic reticulum (ER). ER is responsible for assembly and folding of secreted proteins. When the load on the ER surpasses its capacity, three stress sensors (activating transcription factor 6 [ATF6], inositol-requiring enzyme 1α [IRE1α]/X-box binding protein 1 [XBP1], and PERK/ATF4) are activated to expand the ER and increase its folding capacity. This is referred to as the unfolded protein response (UPR). Here, we hypothesized that there is a reciprocal relationship between SMC differentiation and the UPR. Tight negative correlations between SMC markers (MYH11, MYOCD, KCNMB1, SYNPO2) and UPR markers (SDF2L1, CALR, MANF, PDIA4) were seen in microarray data sets from carotid arterial injury, partial bladder outlet obstruction, and bladder denervation, respectively. The UPR activators dithiothreitol (DTT) and tunicamycin (TN) activated the UPR and reduced MYOCD along with SMC markers in vitro. The IRE1α inhibitor 4μ8C counteracted the effect of DTT and TN on SMC markers and MYOCD expression. Transfection of active XBP1s was sufficient to reduce both MYOCD and the SMC markers. MRTFs also antagonized the UPR as indicated by reduced TN and DTT-mediated induction of CRELD2, MANF, PDIA4, and SDF2L1 following overexpression of MRTFs. The latter effect did not involve the newly identified MYOCD/SRF target MSRB3, or reduced production of either XBP1s or cleaved ATF6. The UPR thus counteracts SMC differentiation via the IRE1α/XBP1 arm of the UPR and MYOCD repression.
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| 5. |
- Zhu, Baoyi, et al.
(författare)
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Nexilin/NEXN controls actin polymerization in smooth muscle and is regulated by myocardin family coactivators and YAP
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Nexilin, encoded by the NEXN gene, is expressed in striated muscle and localizes to Z-discs, influencing mechanical stability. We examined Nexilin/NEXN in smooth muscle cells (SMCs), and addressed if Nexilin localizes to dense bodies and dense bands and whether it is regulated by actin-controlled coactivators from the MRTF (MYOCD, MKL1, MKL2) and YAP/TAZ (YAP1 and WWTR1) families. NEXN expression in SMCs was comparable to that in striated muscles. Immunofluorescence and immunoelectron microscopy suggested that Nexilin localizes to dense bodies and dense bands. Correlations at the mRNA level suggested that NEXN expression might be controlled by actin polymerization. Depolymerization of actin using Latrunculin B repressed the NEXN mRNA and protein in bladder and coronary artery SMCs. Overexpression and knockdown supported involvement of both YAP/TAZ and MRTFs in the transcriptional control of NEXN. YAP/TAZ and MRTFs appeared equally important in bladder SMCs, whereas MRTFs dominated in vascular SMCs. Expression of NEXN was moreover reduced in situations of SMC phenotypic modulation in vivo. The proximal promoter of NEXN conferred control by MRTF-A/MKL1 and MYOCD. NEXN silencing reduced actin polymerization and cell migration, as well as SMC marker expression. NEXN targeting by actin-controlled coactivators thus amplifies SMC differentiation through the actin cytoskeleton, probably via dense bodies and dense bands.
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