Regulation of smooth muscle alpha-actin expression and hypertrophy in cultured mesangial cells.
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.
Department of Pathology, Eastern Virginia Medical School, Norfolk 23501-1980, USA.
L A
LA
Stephenson
L B
LB
Haney
I M
IM
Hussaini
L R
LR
Karns
W F
WF
Glass
D000199:Actins / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D000077214:Becaplermin; D002417:Cattle; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D005786:Gene Expression Regulation / Q000187:drug effects; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D006984:Hypertrophy; D051379:Mice; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013917:Thrombin / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D000199:Actins; D016895:Culture Media, Serum-Free; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D000077214:Becaplermin; D013917:Thrombin