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  • Title: Regulation of smooth muscle alpha-actin expression and hypertrophy in cultured mesangial cells.
    Author: Stephenson LA, Haney LB, Hussaini IM, Karns LR, Glass WF.
    Journal: Kidney Int; 1998 Oct; 54(4):1175-87. PubMed ID: 9767533.
    Abstract:
    BACKGROUND: Mesangial cells during embryonic development and glomerular disease express smooth muscle alpha-actin (alpha-SMA). We were therefore surprised when cultured mesangial cells deprived of serum markedly increased expression of alpha-SMA. Serum-deprived mesangial cells appeared larger than serum-fed mesangial cells. We hypothesized that alpha-SMA expression may be more reflective of mesangial cell hypertrophy than hyperplasia. METHODS: Human mesangial cells were cultured in medium alone or with fetal bovine serum, thrombin, platelet-derived growth factor-BB (PDGF-BB) and/or transforming growth factor-beta1 (TGF-beta1). Alpha-SMA expression was examined by immunofluorescence, Western blot, and Northern blot analysis. Cell size was analyzed by forward light scatter flow cytometry. RESULTS: Alpha-SMA mRNA was at least tenfold more abundant after three to five days in human mesangial cells plated without serum, but beta-actin mRNA was unchanged. Serum-deprived cells contained 5.3-fold more alpha-SMA after three days and 56-fold more after five days by Western blot. Serum deprivation also increased alpha-SMA in rat and mouse mesangial cells. The effects of serum deprivation on alpha-SMA expression were reversible. Mesangial cell mitogens, thrombin or PDGF-BB, decreased alpha-SMA, but TGF-beta1 increased alpha-SMA expression and slowed mesangial cell proliferation in serum-plus medium. Flow cytometry showed that serum deprivation or TGF-beta1 treatment caused mesangial cell hypertrophy. PDGF-BB, thrombin, or thrombin receptor-activating peptide blocked hypertrophy in response to serum deprivation. CONCLUSIONS: We conclude that increased alpha-SMA expression in mesangial cells reflects cellular hypertrophy rather than hyperplasia.
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