Although it is known that the expression and activity of sirtuin 1 (Sirt1) decrease in the aged kidney, the role of interaction between Sirt1 and hypoxia‐inducible factor (HIF)‐1α is largely unknown. In this study, we investigated whether HIF‐1α could be a deacetylation target of Sirt1 and the effect of their interaction on age‐associated renal injury. Five‐week‐old (young) and 24‐month‐old (old) C57Bl/6J mice were assessed for their age‐associated changes. Kidneys from aged mice showed increased infiltration of CD68‐positive macrophages, higher expression of extracellular matrix (ECM) proteins, and more apoptosis than young controls. They also showed decreased Sirt1 expression along with increased acetylated HIF‐1α. The level of Bcl‐2/adenovirus E1B‐interacting protein 3, carbonic anhydrase 9, Snail, and transforming growth factor‐β1, which are regulated by HIF‐1α, was significantly higher in aged mice suggesting that HIF‐1α activity was increased. In HK‐2 cells, Sirt1 inhibitor sirtinol and siRNA‐mediated knockdown of Sirt1 enhanced apoptosis and ECM accumulation. During hypoxia, Sirt1 was down‐regulated, which allowed the acetylation and activation of HIF‐1α. Resveratrol, a Sirt1 activator, effectively prevented hypoxia‐induced production of ECM proteins, mitochondrial damage, reactive oxygen species generation, and apoptosis. The inhibition of HIF‐1α activity by Sirt1‐induced deacetylation of HIF‐1α was confirmed by Sirt1 overexpression under hypoxic conditions and by resveratrol treatment or Sirt1 overexpression in HIF‐1α‐transfected HK‐2 cells. Finally, we confirmed that chronic activation of HIF‐1α promoted apoptosis and fibrosis, using tubular cell‐specific HIF‐1α transgenic mice. Taken together, our data suggest that Sirt1‐induced deacetylation of HIF‐1α may have protective effects against tubulointerstitial damage in aged kidney.

Mesenchymal stem cells (MSCs) are a popular cell source for stem cell‐based therapy. However, continuous ex vivo expansion to acquire large amounts of MSCs for clinical study induces replicative senescence, causing decreased therapeutic efficacy in MSCs. To address this issue, we investigated the effect of melatonin on replicative senescence in MSCs. In senescent MSCs (late passage), replicative senescence decreased mitophagy by inhibiting mitofission, resulting in the augmentation of mitochondrial dysfunction. Treatment with melatonin rescued replicative senescence by enhancing mitophagy and mitochondrial function through upregulation of heat shock 70 kDa protein 1L (HSPA1L). More specifically, we found that melatonin‐induced HSPA1L binds to cellular prion protein (PrP^C), resulting in the recruitment of PrP^C into the mitochondria. The HSPA1L‐PrP^C complex then binds to COX4IA, which is a mitochondrial complex IV protein, leading to an increase in mitochondrial membrane potential and anti‐oxidant enzyme activity. These protective effects were blocked by knockdown of HSPA1L. In a murine hindlimb ischemia model, melatonin‐treated senescent MSCs enhanced functional recovery by increasing blood flow perfusion, limb salvage, and neovascularization. This study, for the first time, suggests that melatonin protects MSCs against replicative senescence during ex vivo expansion for clinical application via mitochondrial quality control.

The accumulation of extracellular matrix proteins in the interstitial area is the final common feature of chronic kidney diseases. Accumulating evidence suggests that transforming growth factor (TGF)-β1 promotes the development of renal fibrosis. Heat shock protein (Hsp) 90 inhibitors have been shown to repress TGF-β1 signaling, but whether they inhibit renal fibrosis is unknown. The purpose of this study is to determine the therapeutic efficacy of Hsp90 inhibitor on renal fibrosis. In TGF-β1-treated HK2 cells and unilateral ureteral obstruction (UUO) kidneys, we found that 17-allylamino-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, decreased the expression of α-smooth muscle actin, fibronectin, and collagen I and largely restored the expression of E-cadherin. 17AAG inhibited TGF-β1-mediated phosphorylation of Smad2, Akt, glycogen synthase kinase-3β, and extracellular signal-regulated kinase in HK2 cells. Inhibition of Hsp90 also blocked TGF-β1-mediated induction of snail1. This 17AAG-induced reduction was completely restored by simultaneous treatment with proteasome inhibitor MG132. Furthermore, 17AAG blocked the interaction between Hsp90 and TGF-β type II receptor (TβRII) and promoted ubiquitination of TβRII, leading to the decreased availability of TβRII. Smurf2-specific siRNA reversed the ability of 17AAG to inhibit TGF-β1 signaling. The effect of 17AAG on TβRII expression and renal fibrosis was confirmed in UUO kidneys. These findings suggest that Hsp90 inhibitor prevents the development of renal fibrosis via a mechanism dependent on Smurf2-mediated degradation of TβRII.

Diabetic nephropathy (DN) is associated with high risk of cardiovascular disease and mortality. Exosomal microRNAs (miRNAs) regulate gene expression in a variety of tissues and play important roles in the pathology of various diseases. We hypothesized that the exosomal miRNA profile would differ between DN patients and patients without nephropathy. We prospectively enrolled 74 participants, including healthy volunteers (HVs), diabetic patients without nephropathy, and those with DN. The serum exosomal miRNA profiles of participants were examined using RNA sequencing. The expression levels of 107 miRNAs differed between HVs and patients without DN, whereas the expression levels of 95 miRNAs differed between HVs and patients with DN. Among these miRNAs, we found 7 miRNAs (miR-1246, miR-642a-3p, let-7c-5p, miR-1255b-5p, let-7i-3p, miR-5010-5p, miR-150-3p) that were uniquely up-regulated in DN patients compared to HVs, and miR-4449 that was highly expressed in DN patients compared to patients without DN. A pathway analysis revealed that these eight miRNAs are likely involved in MAPK signaling, integrin function in angiogenesis, and regulation of the AP-1 transcription factor. Moreover, they were all significantly correlated with the degree of albuminuria. Patients with DN have a different serum exosomal miRNA profile compared to HVs. These miRNAs may be promising candidates for the diagnosis and treatment of DN and cardiovascular disease.

Chronic kidney disease (CKD) is associated with increased risk for cardiovascular diseases (CVD). We hypothesized that inadequate angiogenic response in uremic patients could result from dysfunction of bone marrow-derived stromal cells [mesenchymal stem cells (MSCs)]. We investigated whether MSCs are functionally competent in uremia induced by partial kidney ablation in C57Bl/6J mice. Uremic MSCs showed decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)1 and stromal cell-derived factor (SDF)-1α, increased cellular senescence, decreased proliferation, defects in migration in response to VEGF and SDF-1α and in vitro tube formation. Interestingly, the expression of fibroblast-specific protein-1 was higher in uremic MSCs. Uremia decreased hypoxia-inducible factor-1α, VEGF and VEGFR1 expression under hypoxia and Akt phosphorylation in both basal and VEGF-stimulated states. A diminished mitogenic effect on endothelial proliferation was observed in conditioned media from uremic MSCs. In addition, intravital microscopic analysis showed decreased angiogenesis in uremic MSCs. These results clearly demonstrate the functional incompetence in MSCs under uremic conditions and may significantly contribute to the disproportionately high risk for CVD in patients with CKD.