Smad4 controls proliferation of interstitial cells in the neonatal kidney

Therapeutic potential for renal fibrosis by targeting Smad3-dependent noncoding RNAs

Renal fibrosis is a characteristic hallmark of chronic kidney disease (CKD) that ultimately results in renal failure, leaving patients with few therapeutic options. TGF-β is a master regulator of renal fibrosis and mediates progressive renal fibrosis via both canonical and noncanonical signaling pathways. In the canonical Smad signaling, Smad3 is a key mediator in tissue fibrosis and mediates renal fibrosis via a number of noncoding RNAs (ncRNAs). In this regard, targeting Smad3-dependent ncRNAs may offer a specific therapy for renal fibrosis. This review highlights the significance and innovation of TGF-β/Smad3-associated ncRNAs as biomarkers and therapeutic targets in renal fibrogenesis. In addition, the underlying mechanisms of these ncRNAs and their future perspectives in the treatment of renal fibrosis are discussed.

Nephron progenitors rhythmically alternate between renewal and differentiation phases that synchronize with kidney branching morphogenesis

The mammalian kidney achieves massive parallelization of function by exponentially duplicating nephron-forming niches during development. Each niche caps a tip of the ureteric bud epithelium (the future urinary collecting duct tree) as it undergoes branching morphogenesis, while nephron progenitors within niches balance self-renewal and differentiation to early nephron cells. Nephron formation rate approximately matches branching rate over a large fraction of mouse gestation, yet the nature of this apparent pace-maker is unknown. Here we correlate spatial transcriptomics data with branching 'life-cycle' to discover rhythmically alternating signatures of nephron progenitor differentiation and renewal across Wnt, Hippo-Yap, retinoic acid (RA), and other pathways. We then find in human stem-cell derived nephron progenitor organoids that Wnt/β-catenin-induced differentiation is converted to a renewal signal when it temporally overlaps with YAP activation. Similar experiments using RA activation indicate a role in setting nephron progenitor exit from the naive state, the spatial extent of differentiation, and nephron segment bias. Together the data suggest that nephron progenitor interpretation of consistent Wnt/β-catenin differentiation signaling in the niche may be modified by rhythmic activity in ancillary pathways to set the pace of nephron formation. This would synchronize nephron formation with ureteric bud branching, which creates new sites for nephron condensation. Our data bring temporal resolution to the renewal vs. differentiation balance in the nephrogenic niche and inform new strategies to achieve self-sustaining nephron formation in synthetic human kidney tissues.

ZEB2 controls kidney stromal progenitor differentiation and inhibits abnormal myofibroblast expansion and kidney fibrosis

FOXD1+ cell-derived stromal cells give rise to pericytes and fibroblasts that support the kidney vasculature and interstitium but are also major precursors of myofibroblasts. ZEB2 is a SMAD-interacting transcription factor that is expressed in developing kidney stromal progenitors. Here we show that Zeb2 is essential for normal FOXD1+ stromal progenitor development. Specific conditional knockout of mouse Zeb2 in FOXD1+ stromal progenitors (Zeb2 cKO) leads to abnormal interstitial stromal cell development, differentiation, and kidney fibrosis. Immunofluorescent staining analyses revealed abnormal expression of interstitial stromal cell markers MEIS1/2/3, CDKN1C, and CSPG4 (NG2) in newborn and 3-week-old Zeb2-cKO mouse kidneys. Zeb2-deficient FOXD1+ stromal progenitors also took on a myofibroblast fate that led to kidney fibrosis and kidney failure. Cell marker studies further confirmed that these myofibroblasts expressed pericyte and resident fibroblast markers, including PDGFRβ, CSPG4, desmin, GLI1, and NT5E. Notably, increased interstitial collagen deposition associated with loss of Zeb2 in FOXD1+ stromal progenitors was accompanied by increased expression of activated SMAD1/5/8, SMAD2/3, SMAD4, and AXIN2. Thus, our study identifies a key role of ZEB2 in maintaining the cell fate of FOXD1+ stromal progenitors during kidney development, whereas loss of ZEB2 leads to differentiation of FOXD1+ stromal progenitors into myofibroblasts and kidney fibrosis.