TGF-beta1 and Mitochondrial Dysfunction in LPS-Induced Renal Failure

Medical University Of South Carolina, Charleston SC

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Abstract

DESCRIPTION (provided by applicant): Cell injury and death induced by sepsis, ischemia/reperfusion (I/R), drugs, and trauma lead to failure of many organs, including the kidney. Mitochondrial dysfunction is a common consequence of these insults and a major mechanism of cell injury and death. While mitochondrial dysfunction occurs after AKI, the state and role of mitochondrial function during the injury and recovery phases of sepsis-induced AKI remain unclear. We recently examined renal and mitochondrial function over time in a lipopolysaccharide (LPS) model of sepsis in mice. Glomerular filtration was normal at 18 h but decreased (i.e. elevated serum creatinine) 42 h after LPS injection. Urine output was minimal at 42 h. Mitochondrial electron transport chain and ATP synthesis proteins [i.e. NDUFB8, COX I and ATP synthase ¿ (ATPS ¿)] were depleted at 42 h after LPS injection. Protein levels of PGC-1¿, the master regulator of mitochondrial biogenesis, were also reduced at 42 h. These findings reveal that impaired mitochondrial function is a critical event in LPS-induced AKI. We previously reported that transforming growth factor (TGF) ¿1 is a potent and rapid inhibitor of mitochondrial function in primary cultures of renal proximal tubular cells (RPTC). We show that renal TGF- ¿1 increased following LPS injection in mice. Furthermore, blockade of TGF- ¿1 receptor signaling after LPS-induced AKI improved renal function and restored PGC-1¿ gene expression in the kidney at 42 h. We hypothesize that LPS-induced production of renal TGF- ¿1 suppresses mitochondrial function and biogenesis, and delays recovery of mitochondrial and renal function following AKI. We will examine this hypothesis with two Specific Aims. Specific Aim 1 is to determine the mechanism of TGF- ¿1-induced mitochondrial suppression in LPS-induced AKI in mice. Specific Aim 2 is to determine the effect of TGF- ¿1 blockade on recovery of mitochondrial and renal function in LPS-induced AKI in mice. We will use pharmacological and genetic models of TGF- ¿ pathway inhibition and examine renal mitochondrial function using intravital confocal multiphoton microscopy (ICMM) as well as ex vivo measures of mitochondrial respiration and homeostasis to address these aims. Dr. Stallons will acquire advanced training in new research methodologies including ICMM and flow cytometric determination of renal inflammatory cells. Career development is another focus of the Training Plan, and Dr. Stallons will gain experience in grant writing, scientific presentations, and teaching during this fellowship. The long-term goal of this project are 1) to elucidate the mechanisms of sepsis-induced acute kidney injury (AKI) and the recovery thereof and 2) to develop Dr. Stallons' scientific and communication skills in order to prepare him to compete for a career development award and pursue a career in academic research.