Connective tissue growth factor modulates podocyte actin cytoskeleton and extracellular matrix synthesis and is induced in podocytes upon injury

Abstract

Structural changes of podocytes and retraction of their foot processes are a critical factor in the pathogenesis of minimal change nephritis and glomerulosclerosis. Here we tested, if connective tissue growth factor (CTGF) is involved in podocyte injury during acute and chronic puromycin aminonucleoside nephrosis (PAN) as animal models of minimal change nephritis, and focal segmental glomerulosclerosis, respectively. Rats were treated once (acute PAN) or for 13 weeks (chronic PAN). In both experimental conditions, CTGF and its mRNA were found to be highly upregulated in podocytes. The upregulation correlated with onset and duration of proteinuria in acute PAN, and glomerulosclerosis and high expression of glomerular fibronectin, and collagens I, III, and IV in chronic PAN. In vitro, treatment of podocytes with recombinant CTGF increased amount and density of actin stress fibers, the expression of actin-associated molecules such as podocalyxin, synaptopodin, ezrin, and actinin-4, and activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Moreover, we observed increased podocyte expression of mRNA for transforming growth factor (TGF)-β2, TGF-β receptor II, fibronectin, and collagens I, III, and IV. Treatment of cultured podocytes with puromycin aminonucleoside resulted in loss of actin stress fibers and cell death, effects that were partially prevented when CTGF was added to the culture medium. Depletion of CTGF mRNA in cultured podocytes by RNA interference reduced both the number of actin stress fibers and the expression of actin-associated molecules. We propose that the expression of CTGF is acutely upregulated in podocytes as part of a cellular attempt to repair structural changes of the actin cytoskeleton. When the damaging effects on podocyte structure and function persist chronically, continuous CTGF expression in podocytes is a critical factor that promotes progressive accumulation of glomerular extracellular matrix and glomerulosclerosis.

Genetic Analysis of Connective Tissue Growth Factor as an Effector of Transforming Growth Factor β Signaling and Cardiac Remodeling

“…CTGF is thought to function as a matricellular protein, where it affects cellular interactions through integrins, heparin sulfate proteoglycans (44,45), and possibly other uncharacterized binding partners. CTGF was previously implicated as a secreted growth factor, where it can function when applied directly to the medium in cultured cells (46,47). However, a CTGF receptor has not been identified, so it is unclear how CTGF might otherwise modify cellular responses to injury as a traditional paracrine factor.…”

Intraocular Pressure Homeostasis: Maintaining Balance in a High-Pressure Environment

“…49,55,56,66 Many of these genes have dramatic effects on the TM and on outflow. 15,[67][68][69][70] The same can be said for the cytoskeletal changes. Many cytoskeletal manipulations have dramatic effects on both outflow facility and TM cell behavior.…”

“…[89][90][91][92][93][94][95] An array of other related ECM effects are also likely involved, but IOP homeostatic relationships are not well defined for any of these. 15,67,68,96,97 …”

Aldosterone effects on glomerular structure and function

“…49 Interestingly, it has been shown that CTGF induces mesangial cell cycle arrest, mesangial cell hypertrophy, and mesangial matrix expansion in renal nonepithelial cells, 50 as well as that CTGF can damage the slit diaphragm. 51 Moreover, treatment of diabetic mice with CTGF antisense oligonucleotide attenuates albuminuria. 52 In conclusion, our work further characterizes the effects of aldosterone on the glomerulus.…”