Autophagy is induced in renal tubular cells during acute kidney injury, however, whether this is protective or injurious remains controversial. We address this question by pharmacologic and genetic blockade of autophagy using mouse models of cisplatin- and ischemia-reperfusion induced acute kidney injury. Chloroquine, a pharmacological inhibitor of autophagy, blocked autophagic flux and enhanced acute kidney injury in both models. Rapamycin, however, activated autophagy and protected against cisplatin-induced acute kidney injury. We also established a renal proximal tubule-specific autophagy-related gene 7 knockout mouse model shown to be defective in both basal and cisplatin induced autophagy in kidneys. Compared with wild-type littermates, these knockout mice were markedly more sensitive to cisplatin-induced acute kidney injury as indicated by renal functional loss, tissue damage, and apoptosis. Mechanistically, these knockout mice had heightened activation of p53 and c-Jun N terminal kinase, signaling pathways contributing to cisplatin acute kidney injury. Proximal tubular cells isolated from the knockout mice were more sensitive to cisplatin-induced apoptosis than cells from wild-type mice. In addition, the knockout mice were more sensitive to renal ischemia-reperfusion injury than their wild-type littermates. Thus, our results establish a renoprotective role of tubular cell autophagy in acute kidney injury where it may interfere with cell killing mechanisms.

Autophagy mediates bulk degradation and recycling of cytoplasmic constituents to maintain cellular homeostasis. In response to stress , autophagy is induced and may either contribute to cell death or serve as a cell survival mechanism. Very little is known about autophagy in renal pathophysiology. This study examined autophagy and its pathological role in renal cell injury using in vitro and in vivo models of ischemia؊reperfusion. We found that hypoxia (1% O 2 ) induced autophagy in cultured renal proximal tubular cells. Blockade of autophagy by 3-methyladenine or small-interfering RNA knockdown of Beclin-1 and ATG5 (two key autophagic genes) sensitized the tubular cells to hypoxia-induced apoptosis.In an in vitro model of ischemia؊reperfusion , autophagy was not induced by anoxic (0% O 2 ) incubation in glucose-free buffer , but was induced during subsequent recovery/reperfusion period. In this model, suppression of autophagy also enhanced apoptosis. In vivo, autophagy was induced in kidney tissues during renal ischemia؊reperfusion in mice. Autophagy was not obvious during the ischemia period, but was significantly enhanced during reperfusion. Inhibition of autophagy by chloroquine and 3-methyladenine worsened renal ischemia/reperfusion injury , as indicated by renal function , histology , and tubular apoptosis. Together , the results demonstrated autophagy induction during hypoxic and ischemic renal injury. Under these pathological conditions , autophagy may provide a protective mechanism for cell survival. Autophagy is a cellular process of "self-eating" wherein various cytoplasmic constituents are broken down and recycled through the lysosomal degradation pathway. 1This process consists of several sequential steps, including sequestration of cytoplasmic portions by isolation membrane to form autophagosome, fusion of the autophagosome with lysosome to create an autolysosome, and degradation of the engulfed material to generate monomeric units such as amino acids.2 Identification of the autophagy-related genes (ATG) in yeast and their orthologs in other organisms including mammals demonstrates that autophagy is evolutionarily conserved in all eukaryotic cells. The ATG genes constitute the core molecular machinery of autophagy and function at the different levels to regulate autophagy induction, progression, and completion. 1 Autophagy occurs at basal level in most cells and contributes to the turnover of long-lived proteins and organelles to maintain intracellular homeostasis. In response to cellular stress, autophagy is up-regulated and can provide an adaptive strategy for cell survival, but may also directly or indirectly lead to cell demise. [3][4][5][6] With the dual role in life and death, autophagy is involved in various physiological processes, and more importantly, linked to the pathogenesis of a wide array of diseases, such as neurodegeneration, cancer, heart disease, aging, and infections.1,2,6,7 However, it remains largely unknown how autophagy makes the life and death decisions of a stressed cell. ...

Autophagy is a cellular process of bulk degradation of damaged organelles, protein aggregates and other macromolecules in the cytoplasm. It is thought to be a general response to stress contributing to cell death; alternatively it might act as a cytoprotective mechanism. Here we found that administration of cisplatin induced the formation of autophagic vesicles and autophagosomes in mouse kidneys. In cultured proximal tubular cells, the nephrotoxin caused autophagy in a dose- and time-dependent manner prior to apoptosis. Notably, autophagy occurred within hours of cisplatin administration but this was partially suppressed by the p53 inhibitor pifithrin-alpha, suggesting that p53 is involved in autophagic signaling. This cisplatin-induced autophagy was attenuated in renal cells stably transfected with Bcl-2, suggesting an anti-autophagic role for this well-known anti-apoptotic protein. Blockade of autophagy with pharmacological inhibitors (3-methyladenine or bafilomycin) or shRNA knockdown of the autophagic gene Beclin increased tubular cell apoptosis during cisplatin treatment. Our study has found that autophagy occurs in acute kidney injury and this may be an important protective mechanism for cell survival.

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Autophagy is a highly conserved process that degrades cellular long-lived proteins and organelles. Accumulating evidence indicates that autophagy plays a critical role in kidney maintenance, diseases and aging. Ischemic, toxic, immunological, and oxidative insults can cause an induction of autophagy in renal epithelial cells modifying the course of various kidney diseases. This review summarizes recent insights on the role of autophagy in kidney physiology and diseases alluding to possible novel intervention strategies for treating specific kidney disorders by modifying autophagy.

. Role of p53 in cisplatin-induced tubular cell apoptosis: dependence on p53 transcriptional activity.

Cisplatin is a widely used cancer therapy drug that unfortunately has major side effects in normal tissues, notably nephrotoxicity in kidneys. Despite intensive research, the mechanism of cisplatin-induced nephrotoxicity remains unclear, and renoprotective approaches during cisplatin-based chemotherapy are lacking. Here we have identified PKCδ as a critical regulator of cisplatin nephrotoxicity, which can be effectively targeted for renoprotection during chemotherapy. We showed that early during cisplatin nephrotoxicity, Src interacted with, phosphorylated, and activated PKCδ in mouse kidney lysates. After activation, PKCδ regulated MAPKs, but not p53, to induce renal cell apoptosis. Thus, inhibition of PKCδ pharmacologically or genetically attenuated kidney cell apoptosis and tissue damage, preserving renal function during cisplatin treatment. Conversely, inhibition of PKCδ enhanced cisplatin-induced cell death in multiple cancer cell lines and, remarkably, enhanced the chemotherapeutic effects of cisplatin in several xenograft and syngeneic mouse tumor models while protecting kidneys from nephrotoxicity. Together these results demonstrate a role of PKCδ in cisplatin nephrotoxicity and support targeting PKCδ as an effective strategy for renoprotection during cisplatin-based cancer therapy.

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