Gut Microbial-Derived Short-Chain Fatty Acids Enhance Kidney Proximal Tubule Cell Secretory Function

Background: The organic anion transporter-1 (OAT1) in kidney proximal tubule cells is actively involved in metabolic waste excretion, including uremic toxins; yet its activity becomes impaired upon kidney disease development. Chronic kidney disease also leads to gut dysbiosis, resulting in an increased production of uremic toxins and a reduced production of nephroprotective short chain fatty acid (SCFAs), mainly acetate, propionate and butyrate, thereby contributing to disease progression. Here, we studied whether SCFAs can modulate OAT1 in human kidney proximal tubule cells and stimulate uremic toxin excretion. Methods: The conditionally immortalized human proximal tubule epithelial cell line overexpressing OAT1 (ciPTEC-OAT1) were exposed to SCFAs for 24h at 1 mM alone or in combination (mix). OAT1 activity was measured using fluorescein as substrate and confirmed with a kidney-on-chip (KoC) system perfused basolateral with the uremic toxin and natural substrate, indoxyl sulfate (IS). Gene and protein expression of OAT1 were analyzed along with histone deacetylase (HDAC) inhibition. Bulk RNA sequencing was used to evaluate gene expression signatures. Results: Propionate and butyrate significantly boosted OAT1 activity (p<0.001) by upregulating SLC22A6 gene (p<0.001) encoding for OAT1 protein expression (p<0.05), with butyrate enhancing the secretion of IS to the luminal compartment in our KoC system (p<0.05). Interestingly, SCFAs were shown to act independently of GPCR activation, while instead inhibiting gene expression of class II HDAC enzymes (acetate, p<0.05; propionate and butyrate, p<0.01; SFCA mix, p<0.001). Transcriptome analysis suggests HDAC inhibition affects the cAMP signaling pathway, activating CREB1 and PI3K gene expressions. These regulate cell metabolism and stress responses, promote proliferation and survival, enhance SLC22A6/OAT1 function, supporting overall cellular health, function, and resilience, thus enhancing cellular fitness. Conclusion: Propionate and butyrate exert a significant enhancement of OAT1 activity through SLC22A6 gene upregulation. Further investigations into the direct effects of SCFAs could potentially introduce them as a novel and effective approach for restoring impaired OAT1 function and maintaining kidney health. This project was funded by EU Horizon 2020 MC STRATEGY-CKD (860329). Funding: Government Support – Non-U.S.