Survivin Mediates Renal Proximal Tubule Recovery from AKI

Abstract

AKI induces the renoprotective upregulation of survivin expression in kidney epithelial cells, but the underlying mechanisms have not been identified. To determine the role of survivin in renal recovery from AKI, we generated mice with renal proximal tubule-specific deletion of survivin (survivin ptKO ). Renal survivin expression increased substantially in response to ischemia-reperfusion (I/R) injury in control littermates but remained minimal in survivin ptKO mice. Functional and histologic data indicated similar degrees of renal injury in survivin ptKO and control mice 24 hours after reperfusion, but recovery was markedly delayed in survivin ptKO mice. In MCT cells, a mouse renal proximal tubule cell line, ATP depletion by antimycin A treatment upregulated survivin expression through a phospho-STAT3-dependent pathway. In wild-type mice, inhibition of STAT3 kinase diminished I/R-induced upregulation of STAT3 phosphorylation and survivin expression and delayed recovery. Furthermore, I/R injury activated Notch-2 signaling, and a g-secretase inhibitor suppressed I/R-induced Notch-2 signaling, STAT3 phosphorylation, and survivin expression and delayed recovery. In MCT cells, inhibition of g-secretase similarly attenuated antimycin A-induced Notch-2 activation, upregulation of survivin, and phosphorylation of STAT3, but STAT3 kinase inhibition did not prevent Notch-2 activation. Therefore, these data suggest that STAT3 phosphorylation and subsequent upregulation of survivin expression mediated by Notch-2 signaling in renal proximal tubule epithelial cells aid in the functional and structural recovery of the kidney from AKI. AKI is a common clinical condition encountered in both hospital and outpatient settings, and it is an important cause of morbidity and mortality. Approximately 600,000 cases of AKI are reported each year in the United States. 1 Despite significant preclinical and clinical research, supportive therapy remains the only treatment option for AKI patients, and to date, the mortality rates of AKI remain high. 2 It has also become increasingly clear that AKI is associated with the development of CKD. 3,4 Ischemia-reperfusion (I/R) injury is one of the most common causes of AKI in clinical practice, and the underlying pathogenesis involves injury to nephron segments from both the ischemia itself and the resulting inflammatory response. The S3 segment of proximal tubules is most vulnerable to I/R injury. 5 As a result of I/R injury, renal proximal tubule cells exhibit mitochondrial dysfunction, ATP depletion, impaired solute and ion transport, loss of cell polarity, and cytoskeletal disruption, 6 and they may ultimately undergo apoptosis or necrosis.The kidney has a remarkable capacity for regeneration, which is evidenced by the ability to recover renal function after moderate I/R injury.

Severity and Frequency of Proximal Tubule Injury Determines Renal Prognosis

“…51,52 Tubular injury was defined as tubular dilation, tubular atrophy, tubular cast formation, vacuolization, degeneration, and sloughing off of tubular epithelial cells or loss of the brush border and thickening of the tubular basement membrane. The tubules were evaluated according to the following scoring system: 0= no tubular injury; 1#10% tubules injured; 2=11%-25% tubules injured; 3=26%-50% tubules injured; 4=51%-74% tubules injured; and 5$75% tubules injured.…”

Inhibition of Notch Signaling Ameliorates Acute Kidney Failure and Downregulates Platelet-Derived Growth Factor Receptor β in the Mouse Model

“…Treatment of ischemic mice with the γ-secretase inhibitor DBZ ameliorated AKI and blocked Notch signaling with specific downregulation of Notch3, Dll4, Jag1 and the Notch target genes Hes1 , Hey2 , HeyL , Pdgfrb and Hif2a , suggesting that interventions targeting this cell-context-specific Notch signaling may be a feasible therapeutic approach. The reactivation of Notch signaling in acutely ischemic kidney and other tissues following ischemic injury has been observed in several studies Bielesz et al, 2010;Gupta et al, 2010;Huang et al, 2011;Liu et al, 2012;Chen et al, 2013;Sorensen-Zender et al, 2014]; however, whether this is beneficial for regeneration or has [Gupta et al, 2010] and blockade of Notch signaling with the γ-secretase inhibitor RO4929097 delayed functional and structural recovery , other studies, in line with this work, indicated the opposite effect, i.e. that the blockade of Notch signaling by the γ-secretase inhibitor DBZ or with a soluble Dll4 fusion protein promotes recovery from AKI or other acute ischemic tissue injuries [Huang et al, 2011;Liu et al, 2012;Sorensen-Zender et al, 2014] tors, Notch1-4, and 5 ligands, Dll1, Dll3, Dll4, Jag1 and Jag2.…”

Blocking rpS6 Phosphorylation Exacerbates Tsc1 Deletion–Induced Kidney Growth

“…For histologic examination, H&E staining was performed using the standard methods. 73 Immunohistochemistry and immunofluorescence staining were performed as described previously. 73,74 Briefly, rehydrated kidney sections were subjected to antigen retrieval using the Antigen Unmasking Solution purchased from Vector, followed by blocking with 2% normal goat serum.…”

“…73 Immunohistochemistry and immunofluorescence staining were performed as described previously. 73,74 Briefly, rehydrated kidney sections were subjected to antigen retrieval using the Antigen Unmasking Solution purchased from Vector, followed by blocking with 2% normal goat serum. The sections were then incubated with primary antibodies (indicated in the respective figures) at 4°C overnight, washed three times in PBS, incubated with appropriate secondary antibodies, and washed with PBS again.…”

“…Immunoblotting analyses were performed as we previously described. [73][74][75] Measurement of Kidney Function BUN levels were measured as we previously described. 17,20 Briefly, blood samples were collected from mice at different ages indicated in the corresponding figures and BUN levels were immediately measured according to the instruction of the commercially available kit, Liquid Urea Nitrogen Reagent Set (Pointe Scientific).…”