Renal Response to Acidosis: RNA‐Seq and Role of NaDC1

Metabolic acidosis is a common pathophysiologic condition that can occur either acutely or chronically in a variety of settings and diseases. Acidosis has a number of adverse effects including progression of chronic kidney disease, bone loss, and muscle wasting. The kidneys are the main organs which respond to acid loads to protect against systemic acidosis. To enhance our understanding of the renal response to acidosis, we performed RNA‐Seq on kidneys from acid loaded animals. Additionally, since NaDC1 (sodium dicarboxylate transporter 1 in the proximal tubule) is known to respond to acidosis, we addressed the role of NaDC1 in the response to acidosis. NaDC1 reabsorbs citrate and various dicarboxylate Krebs cycle intermediates, some of which have downstream G protein coupled receptors. NaDC1 Knockout (KO) and wild type (WT) mice (C57BL/6 background) were studied on normal or acid diet (0.4M HCl added to chow, X 3 days). Kidney RNA was extracted & integrity validated. RNA‐seq was performed at the Tulane Center for Aging Genomics and Biostats Core using an Ion Proton platform with 20M reads/sample. Bioinformatics completed at Tulane Cancer Crusaders NGS Analysis Core. For qRT‐PCR, RNA was isolated from same kidneys & mRNA relative expression was calculated by ΔΔCt. In WT with acidosis, 1173 transcripts were differentially expressed >1.5 fold (each statistically significant), 525 transcripts upregulated and 648 down regulated. Results were similar to prior microarray data (Nowik et al Physiol Genomics 2008). Among those upregulated many have been previously reported to be involved in the response to acidosis: e.g., PCK1, GLUD1, Car2, SNAT1, NaDC1. Also 36 genes from SLC family were identified and differentially expressed under acidosis. By qPCR, SLC genes 13a2, 13a3, 16a9, 26a6 & 38a3 were upregulated & consistent with RNA‐seq. But we also identified many additional genes that indicate a broader cellular metabolic response to acidosis. In contrast, in KO with acidosis many more transcripts (945) were upregulated >1.5 fold and downregulated (1270) >1.5 fold. In sum, metabolic acidosis significantly alters the expression of hundreds of genes, some directly linked to homeostatic responses, but others involving a variety of metabolic and signaling pathways. The response to acidosis in NaDC1 KO mice is even more profound and may indicate that in the absence of NaDC1, additional response pathways are necessary. This implies that NaDC1 plays a more important role in the response to metabolic acidosis than previously recognized.. Support or Funding Information NIH/NIDDK RO1 DK095879