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

Research output: Contribution to journalArticlepeer-review

Abstract

Transforming growth factor-β1 (TGF-β1) is thought to drive fibrogenesis in numerous organ systems. However, we recently established that ectopic expression of TGF-β1 abrogates collagen accumulation via canonical SMAD signaling mechanisms in a shear-induced model of kidney fibrosis. We herein delineate the temporal control of endogenous TGF-β1 signaling that generates sustained synchronous fluctuations in TGF-β1 cascade activation in shear-stimulated proximal tubule epithelial cells (PTECs). During 8-h exposure to physiological shear stress (0.3 dyn/cm2), PTECs experience in situ oscillatory concentrations of active endogenous TGF-β1 that are ~10-fold greater than those detected under higher stress regimes (2-4 dyn/cm2). The elevated levels of intrinsic TGF-β1 maturation observed under physiological conditions are accompanied by persistent downstream SMAD3 activation. Pathological shear stresses (2 dyn/cm2) first elicit temporal variations in phosphorylated SMAD3 with an apparent period of ~6 h, whereas even higher stresses (4 dyn/cm2) abolish SMAD3 activation. These divergent patterns of SMAD3 activation are attributed to varying levels of Notch4-dependent phospho-SMAD3 degradation. Depletion of Notch4 in shear-stimulated PTECs eventually increases the levels of active TGF-β1 protein by approximately fivefold, recovers stable SMAD phosphorylation and ubiquitinated SMAD species, and attenuates collagen accumulation. Collectively, these data establish Notch4 as a critical mediator of shear-induced fibrosis and further reinforce the renoprotective effects of canonical TGF-β1 signaling.

Original languageEnglish (US)
Pages (from-to)F123-F133
JournalAmerican Journal of Physiology - Renal Physiology
Volume305
Issue number1
DOIs
StatePublished - Jul 1 2013

Keywords

  • Chronic kidney disease
  • Fluid shear
  • Frequency dependent signaling
  • Tubulointerstitial fibrosis

ASJC Scopus subject areas

  • Physiology
  • Urology

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