Proximal tubular injury and rapid formation of atubular glomeruli in mice with unilateral ureteral obstruction: a new look at an old model

Abstract

Unilateral ureteral obstruction (UUO), employed extensively as a model of progressive renal interstitial fibrosis, results in rapid parenchymal deterioration. Atubular glomeruli are formed in many renal disorders, but their identification has been limited by labor-intensive available techniques. The formation of atubular glomeruli was therefore investigated in adult male mice subjected to complete UUO under general anesthesia. In this species, the urinary pole of Bowman's capsule is normally lined by tall parietal epithelial cells similar to those of the proximal tubule, and both avidly bind Lotus tetragonolobus lectin. Following UUO, these cells became flattened, lost their affinity for Lotus lectin, and no longer generated superoxide (revealed by nitroblue tetrazolium infusion). Based on Lotus lectin staining, stereological measurements, and serial section analysis, over 80% of glomeruli underwent marked transformation after 14 days of UUO. The glomerulotubular junction became stenotic and atrophic due to cell death by apoptosis and autophagy, with concomitant remodeling of Bowman's capsule to form atubular glomeruli. In this degenerative process, transformed epithelial cells sealing the urinary pole expressed α-smooth muscle actin, vimentin, and nestin. Although atubular glomeruli remained perfused, renin immunostaining was markedly increased along afferent arterioles, and associated maculae densae disappeared. Numerous progressive kidney disorders, including diabetic nephropathy, are characterized by the formation of atubular glomeruli. The rapidity with which glomerulotubular junctions degenerate, coupled with Lotus lectin as a marker of glomerular integrity, points to new investigative uses for the model of murine UUO focusing on mechanisms of epithelial cell injury and remodeling in addition to fibrogenesis.

Persistent activation of autophagy in kidney tubular cells promotes renal interstitial fibrosis during unilateral ureteral obstruction

“…[28][29][30][31][32]35 Using pharmacological and genetic inhibitory approaches, our study has determined the regulation of renal interstitial fibrosis by autophagy in the in vivo model of UUO and in vitro model of TGFB1-treated proximal tubular cells. The results show that blockade of autophagy by pharmacological inhibitors (choloroquine and 3-methyladenine) or conditional Atg7 deletion from proximal tubules suppressed renal interstitial fibrosis during UUO.…”

“…[28][29][30][31][32] The techniques for analyzing autophagy in vivo in those studies mainly include electron microscopy profile of autophagic vesicles, immunohistochemical staining of LC3, GFP-LC3 fluorescent puncta, and conversion of LC3-I to LC3-II. These methods can monitor autophagy at steady-state levels, but they do not reveal the dynamic nature of autophagy.…”

“…23 In the kidney, autophagy appears to occur in the UUO model of kidney fibrosis. [28][29][30][31][32] Also, TGFB1 activates autophagy in renal tubules in mice and in cultured renal tubular and mesangial cells. [33][34][35] Under these conditions, however, the role(s) of autophagy in renal interstitial fibrosis is poorly understood.…”

“…36 On the one hand, autophagy has been suggested to induce tubular atrophy and decomposition to promote fibrosis. 28,29,31,35 On the other hand, autophagy may contribute to the degradation of COL1/collagen I and active TGFB1 to inhibit kidney fibrosis. 32,34 Thus, autophagy regulation in renal fibrosis may be multifaceted and cell-specific.…”

Severity and Frequency of Proximal Tubule Injury Determines Renal Prognosis

“…34,53 The prevalence of atubular glomeruli in the kidneys of Ndrg1 CreERT2/+ :iDTR mice after repeated injections of low-dose DT (n=3) and PBS (n=3) was evaluated as described previously. 23,[54][55][56] Paraffin-embedded kidneys were sectioned at 4-mm intervals for 27 slices for each sample, and the glomeruli in the 14th section were analyzed for continuity with proximal tubules using the consecutive sections. Percentages of atubular glomeruli, which lack any connection to proximal tubules, were determined in each sample.…”