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Dedifferentiation of immortalized human podocytes in response to transforming growth factor-β: a model for diabetic
Michal Herman-Edelstein1, Merlin C Thomas, Vicki Thallas-Bonke
1JDRF Danielle Alberti Memorial Centre for Diabetes Complications,Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria,Australia.
Objective:
Diabetic nephropathy is associated with dedifferentiation of podocytes, losing the specialized features required for efficient glomerular function and acquiring a number of profibrotic, proinflammatory, and proliferative features. These result from tight junction and cytoskeletal rearrangement, augmented proliferation, and apoptosis.
Research Design And Methods:
Experiments were performed in conditionally immortalized human podocytes developed by transfection with the temperature-sensitive SV40-T gene. Cells were then cultured in the presence of transforming growth factor (TGF)-β1 or angiotensin II in the presence or absence of a selective inhibitor of the TGF-β type I receptor kinase, SB-431542. Gene and protein expression were then examined by real-time RT-PCR and immunofluorescence, and correlated with changes observed in vivo in experimental diabetes.
Results:
Treatment of cells with TGF-β1 resulted in dynamic changes in their morphology, starting with retraction and shortening of foot processes and finishing with the formation of broad and complex tight junctions between adjacent podocytes. This dedifferentiation was also associated with dose- and time-dependent reduction in the expression of glomerular epithelial markers (nephrin, p-cadherin, zonnula occludens-1) and increased expression of mesenchymal markers (α-smooth muscle actin, vimentin, nestin), matrix components (fibronectin, collagen I, and collagen IV α3), cellular proliferation, and apoptosis. The induction of diabetes in mice was also associated with similar changes in morphology, protein expression, and proliferation in glomerular podocytes.
Conclusions:
In response to TGF-β and other TGF-dependent stimuli, mature podocytes undergo dedifferentiation that leads to effacement of foot processes, morphologic flattening, and increased formation of intercellular tight junctions. This simplification of their phenotype to a more embryonic form is also associated with reentry of mature podocytes into the cell cycle, which results in enhanced proliferation and apoptosis. These "pathoadaptive" changes are seen early in the diabetic glomerulus and ultimately contribute to albuminuria, glomerulosclerosis, and podocytopenia.
Insights
Diabetic nephropathy causes podocyte dedifferentiation, altering their specialized function. These changes, including proliferation and apoptosis, contribute to kidney disease progression.
Area of Science:
- Nephrology
- Cell Biology
- Diabetic Complications
Background:
- Diabetic nephropathy involves podocyte dedifferentiation, a loss of specialized features.
- This dedifferentiation is linked to profibrotic, proinflammatory, and proliferative changes.
Purpose of the Study:
- To investigate the mechanisms of podocyte dedifferentiation in diabetic nephropathy.
- To examine the role of transforming growth factor-beta 1 (TGF-β1) and angiotensin II in this process.
Main Methods:
- Experiments utilized human podocytes treated with TGF-β1 or angiotensin II.
- Inhibitor SB-431542 was used to block the TGF-β type I receptor kinase.
- Gene and protein expression were analyzed via real-time RT-PCR and immunofluorescence, correlated with in vivo diabetic models.
Main Results:
- TGF-β1 induced podocyte dedifferentiation, characterized by foot process effacement and altered tight junctions.
- A decrease in glomerular epithelial markers and an increase in mesenchymal markers were observed.
- Increased cellular proliferation and apoptosis were noted, mirroring changes seen in experimental diabetes.
Conclusions:
- Mature podocytes dedifferentiate in response to TGF-β, adopting a more embryonic phenotype.
- This dedifferentiation contributes to increased proliferation, apoptosis, and ultimately, kidney damage in diabetic nephropathy.
- These pathoadaptive changes are early indicators of diabetic kidney disease, leading to albuminuria and glomerulosclerosis.
