(614.12) HDAC3 Inhibition Improved Urinary Concentrating Defect in Hypokalemia by Promoting AQP2 Transcription

Poster Board Number: E587

Long Xu (Sun Yat-sen University, Sun Yat-sen University), Haixia Xie (Sun Yat-sen University), Shan Hu (Guangzhou University of Chinese Medicine), Xiaoduo Zhao (Sun Yat-sen University), Mengke Han (Sun Yat-sen University), Qiaojuan Liu (Sun Yat-sen University), Pinning Feng (Sun Yat-sen University), Weidong Wang (Sun Yat-sen University), Chunling Li (Sun Yat-sen University)

Hypokalemia is a common electrolyte disturbance frequently encountered in clinical medicine. Animals with hypokalemia had a significant arginine vasopressin (AVP)-resistant polyuria with reduced expression of aquaporin 2 (AQP2) levels in the collecting ducts of the kidneys. The precise molecular mechanisms of hypokalemia-induced nephrogenic diabetes insipidus remain unresolved. AVP induced a marked increase in histone H3K27 acetylation (H3K27ac) across the body of the AQP2 gene, in the promoter and in upstream of the AQP2 transcriptional start site in mouse mpkCCD cell line (PMID: 29572403). The purpose of the present study was to investigate whether enhanced histone acetylation prevented decreased AQP2 expression and improved urinary concentrating defect in rats with hypokalemia. Male Wistar rats were fed potassium-free diet with or without 4-phenylbutyric acid (4-PBA) or a selective inhibitor of histone deacetylase 3 (HDAC3) RGFP966 for 4 days. 4-PBA or RGFP966 markedly increased AQP2 mRNA and protein levels in kidney inner medulla of rats with hypokalemia, which was associated with decreased urine output and increased urinary osmolality. Protein expression of H3K27ac was markedly decreased in kidney inner medulla of hypokalemic rats, which was significantly prevented by 4-PBA or RGFP966. Expression of H3K27ac was decreased in primary cultured inner medullary collecting duct cells (IMCD) or mpkCCD cells cultured in potassium-deprivation media, in particular, H3K27ac in the promoter region of AQP2 was markedly decreased, which was associated with reduced mRNA levels of AQP2. Protein expression of HDAC3 was significantly upregulated in both mpkCCD and IMCD cells in response to potassium deprivation; the binding of HDAC3 to the promoter of AQP2 was also dramatically increased. RGFP966 significantly increased expression of H3K27ac and AQP2 protein and enhanced the binding of H3K27ac to AQP2 in mpkCCD cells. In conclusion, HDAC3 inhibition prevented downregulation of AQP2 and improved urinary concentrating defect induced by potassium deprivation, likely through enhancing acetylation of H3K27 and transcription of AQP2.  

KEY WORDS: AQP2; hypokalemia; HDAC3, histone acetylation

This work was supported by the National Natural Science Foundation of China (Grant Nos. 81870465, 81970623, 81570635, 81670646), Natural Science Foundation of Guangzhou (201904010255), Natural Science Foundation of Guangdong Province (Nos. 2021A1515011482, 2016A020215034).