We postulated that alpha-smooth muscle actin expressed in primary cultured mesangial cells is down-regulated in 3-dimensional (D) culture and up-regulated by high glucose and growth factors.
Primary rat mesangial cells were growth-arrested in 5.6 mM (NG) or 30 mM (HG) glucose for 14 days in 3-D Matrigel. Alpha-SM actin expression was analyzed by immunoblotting, real-time PCR and by alpha-SM actin promoter activity in response to 24 h stimulation with endothelin-1 (ET-1), angiotensin II (Ang II) or HG.
Alpha-SM actin mRNA, protein and promoter activity were reduced to significantly lower levels in 3-D cells compared to cells in 2-D. Up-regulation of alpha-SM expression was stimulated by ET-1, Ang II and HG. Specific inhibitors of protein kinase C (PKC)-alpha, -beta or -zeta prevented alpha-SM upregulation in HG. In NG, PKC and ERK1/2 activation were required for alpha-SM actin accumulation in 3-D in response to ET-1 or Ang II. In HG, enhanced expression of alpha-SM actin in response to ET-1 or Ang II was unchanged during PKC or ERK1/2 inhibition.
Mesangial cells in 3-D express low levels of alpha-SM actin representing a more differentiated state. Regulation of alpha-SM actin expression is dependent on specific PKC isozyme and ERK1/2 signaling.
[Show abstract][Hide abstract] ABSTRACT: Clinical studies indicate that the remission, regression or both of nephrotic-range albuminuria are exerted by angiotensin II receptor blockers (ARBs) in diabetes. The current study was performed to test the hypothesis that these effects of ARBs are associated with regression of glomerular podocyte injury.
We examined the effects of an ARB, olmesartan, on glomerular podocyte injury in type 2 diabetic Otsuka-Long-Evans-Tokushima-Fatty rats with overt albuminuria.
At baseline (55-week-old), diabetic Otsuka-Long-Evans-Tokushima-Fatty rats showed severe albuminuria with desmin-positive areas (an index of podocyte injury) in both superficial and juxtamedullary glomeruli, and podocyte injury was much greater in juxtamedullary than in superficial glomeruli. At 75-week-old, Otsuka-Long-Evans-Tokushima-Fatty rats had developed more severe albuminuria and superficial glomerular podocyte injury, whereas juxtamedullary glomerular podocyte injury did not advance further. Olmesartan (10 mg/kg per day) decreased albuminuria and superficial glomerular desmin staining to levels that were lower than those at baseline, whereas advanced juxtamedullary glomerular podocyte injury was not changed.
The current study demonstrates for the first time that juxtamedullary glomerular podocyte injury reaches a severe condition at an earlier time than superficial glomerular podocyte injury during the progression of overt albuminuria in type 2 diabetic rats. Our data also support the hypothesis that the antialbuminuric effects of ARBs are associated with regression of superficial glomerular podocyte injury in type 2 diabetes with nephrotic-range albuminuria.
Journal of Hypertension 11/2010; 28(11):2289-98. DOI:10.1097/HJH.0b013e32833dfcda · 4.72 Impact Factor
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