• microRNA Regulation of Acute Kidney Injury

      Bhatt, Kiri; Department of Cellular Biology and Anatomy (2011-08)
      Acute kidney injury (AKI) is caused by an injury or insult to the kidneys resulting in abrupt loss of renal function. Acute kidney injury is a highly prevalent disease characterized by high rates of morbidity and mortality mainly due to the absence of effective therapeutic options. Dissecting the molecular basis of AKI is vital not only for understanding the mechanisms of disease pathogenesis, but also for designing effective treatments. The small regulatory non-coding RNAs, microRNAs, are vital regulators of normal cellular function and critical modulators of various pathological conditions. An intense focus has recently emerged on the study of microRNA regulation in the maintenance of kidney function and the development of renal diseases. Our laboratory demonstrated the first evidence that microRNAs play a pathogenic role during ischemiainduced AKI by utilizing a conditional Dicer knockout mouse model. The focus of my work was to identify and functionally characterize novel microRNAs that contribute to AKI. Firstly, using a cisplatin-induced nephrotoxicity model of AKI, we showed that miR-34a is up-regulated in a p53 dependent manner and contributes to renal cell survival. Secondly, we identified a novel microRNA, miR-687, as the most significantly upregulated microRNA during ischemia-induced AKI. Mechanistic studies showed that miR-687 is up-regulated in a hypoxia-inducible factor 1 (HIFIndependent manner and subsequently negatively regulates PTEN expression under hypoxic conditions. These studies have unearthed an important HIFl-miR-687-PTEN signaling pathway that regulates cell cycle progression during hypoxia. Thirdly, we show that inhibiting miR-687 significantly ameliorates ischemia-induced AKI. These studies have identified a pivotal signaling mechanism involved in cellular response to hypoxia that may be targeted for renoprotection during ischemic AKI.
    • PKC and ATR Mediated Regulation of Cisplatin-Induced Renal Tubular Cell Apoptosis

      Pabla, Navjotsingh; Department of Cellular Biology and Anatomy (2009-03)
      Cisplatin is one of the most widely used anti-cancer drug. However, its use and efficacy is limited due to nephrotoxicity. One fourth of patients treated with cisplatin develop varying degree of renal impairment, frequently resulting in acute kidney injury. Due to high mortality associated with acute kidney injury, effort has been made to understand the molecular basis of cisplatin nephrotoxicity and develop effective renoprotective strategies. In kidneys, cisplatin is accumulated in tubular cells; however the uptake mechanism that is responsible for high accumulation of cisplatin in renal cells is unclear. In tubular cell, cisplatin accumulation induces cell death by apoptosis. Mechanistically, our laboratory has demonstrated a critical role of p53 in tubular cell apoptosis during cisplatin nephrotoxicity. However, the proximal events that contribute to p53 activation and related signaling are unknown. The focus of my work was to decipher these early events during cisplatin nephrotoxicity. Firstly, my results suggest that the copper transporter Ctr1 is highly expressed in renal tubular cells and is responsible for renal uptake of cisplatin. Secondly, I show that DNA damage response involving ATR-Chk2 is responsible for p53 activation and consequent apoptosis during cisplatin-induced kidney injury and nephrotoxicity. Thirdly, I have identified that PKCd is a novel regulator of cisplatin nephrotoxicity. During cisplatin treatment PKCd is activated in a Src dependent manner and is responsible for activation of MAPKs, contributing to renal cell death. Most importantly, my results suggest that pharmacological inhibition of PKCd ameliorates renal injury without affecting the anticancer efficacy of cisplatin. These results have not only provided new insights into the 3 molecular mechanism of cisplatin nephrotoxicity, but have also identified a novel strategy to mitigate the side effects of cisplatin in normal renal tissues.