Epithelial‐mesenchymal transition and fibrosis are mutually exclusive reponses in shear‐activated proximal tubular epithelial cells

Abstract

Renal fibrosis (RF) is thought to be a direct consequence of dedifferentiation of resident epithelial cells via an epithelial-mesenchymal transition (EMT). Increased glomerular flow is a critical initiator of fibrogenesis. Yet, the responses of proximal tubular epithelial cells (PTECs) to fluid flow remain uncharacterized. Here, we investigate the effects of pathological shear stresses on the development of fibrosis in PTECs. Our data reveal that type I collagen accumulation in shear-activated PTECs is accompanied by a ∼40-60% decrease in cell motility, thus excluding EMT as a relevant pathological process. In contrast, static incubation of PTECs with TGFβ1 increases cell motility by ∼50%, and induces stable expression of key mesenchymal markers, including Snail1, N-cadherin, and vimentin. Ectopic expression of TGFβ1 in shear-activated PTECs fails to induce EMT-associated changes but abrogates collagen accumulation via SMAD2-dependent mechanisms. Shear-mediated inhibition of EMT occurs via cyclic oscillations in both ERK2 activity and downstream expression of EMT genes. A constitutive ERK2 mutant induces stable expression of Snail1, N-cadherin, and vimentin, and increases cell motility in shear-activated PTECs by 250% without concomitant collagen deposition. Collectively, our data reveal that RF not only occurs without EMT but also that these two responses represent mutually exclusive cell fates.

Notch4-dependent antagonism of canonical TGF-β1 signaling defines unique temporal fluctuations of SMAD3 activity in sheared proximal tubular epithelial cells

“…Prior work in our laboratory demonstrated that collagen accumulation in shear-activated PTECs increases with the magnitude of applied shear stress, further corroborating the critical role of hyperfiltration on the progression of renal fibrosis (19). Moreover, ectopic expression of TGF-␤1 evinced distinctly anti-fibrotic effects in shear-stimulated cells (19).…”

“…However, we recently demonstrated that not only are EMT and fibrosis mutually exclusive events in sheared proximal tubular epithelial cells (PTECs), but also that ectopic overexpression of TGF-␤1 in these cells abrogates EMTindependent matrix accumulation via SMAD-dependent mechanisms (19). Consistent with these observations, recent work by Fragiadaki and colleagues (16) identified dynamic dosagedependent effects of TGF-␤1, whereby low concentrations stimulate collagen synthesis but high concentrations suppress it.…”

“…Moreover, ectopic expression of TGF-␤1 evinced distinctly anti-fibrotic effects in shear-stimulated cells (19). To more fully characterize the role of canonical TGF-␤1 signaling in shear-induced fibrosis, we examined the time evolution of endogenous TGF-␤1-mediated SMAD activation in the absence of an ectopic expression vector.…”

The cytokines of pulmonary fibrosis: Much learned, much more to learn

“…Thus, it appears that myofibroblasts may arise from a number of non-fibroblast precursor cells, and these precursors may be of resident or non-resident (bone marrow) origin ( Table 1). The epithelial-mesenchymal transition (EMT) is a possible source of myofibroblasts [28,29], although the extent of its contribution to real-life mechanisms of human fibrotic diseases and animal models of fibrosis remains to be established [30][31][32][33]. Similarly, the endothelial-mesenchymal transition (EndoMT) [34] and the mesothelial-mesenchymal transition (MMT) [35][36][37] may contribute to fibrosis.…”

Immunohistochemical study of tubular epithelial cells and vascular endothelial cells in glomerulonephritis

“…The authors conclude that renal fibrosis and EMT could exclude each other. 24 This could be a possible explanation of the fact that in our patients with FSGS tubular aSMA correlated indirectly with interstitial fibrosis, or that it correlated directly with eGFR (in patients with MPGN). It remains, however, difficult to explain why in our patients Vim and aSMA showed different patterns of expression and correlations in TEC.…”