Increasing Our Understanding of Kidney Development and Disease: The Role of Ppargc1a in Segmentation and Ciliopathies

Kidney disease is among the most common disorders in the United States as 37 million Americans suffer from Chronic Kidney Disease (CKD). Unfortunately, current treatments for kidney diseases are lacking and those that do exist, transplantation and dialysis, are either very limited in availability or not suitable for long-term quality of life. Additionally, over 20% of birth defects are Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) making it the most common condition in neonates. A better understanding of kidney development and disease is necessary to improve the lives of those suffering from renal ailments. One tool that can be used to gain a better understanding of the molecular events resulting in kidney development and disease is the embryonic zebrafish. The zebrafish pronephros, or embryonic kidney provides a simple yet conserved nephron structure that allows for rapid results while conducting genetic studies. The numerous benefits of the zebrafish allow for high throughput screens to identify novel roles and interactions among molecular pathways. Here, we performed a chemical genetic screen that identified peroxisome proliferator-activated receptor gamma coactivator 1 alpha (ppargc1a, or PGC-1a) as a novel regulator of kidney ontogeny. Multiple models of ppargc1a deficiency including mutants and morpholino injected zebrafish models were used to interrogate the molecular pathways involved in nephron segmentation. We discovered unique interactions where ppargc1a acts upstream of tbx2b to properly form the distal late tubule domain. Also, data suggests a rare reciprocal antagonistic role between ppargc1a and sim1a to negotiate proximal straight tubule development. Further, loss of ppargc1a results in phenotypes associated with ciliopathies including polycystic kidney disease (PKD). Investigations found ppargc1a is necessary for proper multiciliated cell (MCC) development and ciliogenesis throughout the zebrafish. Interestingly, a novel interaction between ppargc1a and the prostaglandin pathway component cox-1 (ptgs1) was identified as evidence supports the hypothesis that ppargc1a regulates prostaglandin E2 levels via ptgs1 in order to properly develop MCCs and cilia outgrowth in the pronephros. In an attempt to ascertain upstream regulators of ppargc1a we cross referenced known PKD causing genes with literature suggesting relationships with ppargc1a. The transcription factor hepatocyte nuclear factor-1 homeobox β had been shown to regulate renal mitochondria via ppargc1a in human and mice. Interestingly, zebrafish lacking hnf1ba present with similar phenotypes as ppargc1a deficient samples. Because of this, we investigated the relationship further and found a drastic decrease in ppargc1a expression in hnf1ba mutants and ppargc1a overexpression is able to partially rescue the number MCCs in the zebrafish pronephros. By gaining a better understanding of the molecular interactions resulting in disease states such as PKD we can continue to develop approaches to treat or perhaps cure underlying genetic issues that result in decreased quality of life among patients.