Alleviating vascular calcification with Bushen Huoxue formula in rats with chronic kidney disease by inhibiting the PTEN/PI3K/AKT signaling pathway through exosomal microRNA-32.

Background: Vascular calcification (VC) significantly raises cardiovascular mortality in chronic kidney disease (CKD) patients. VC is characterized by the phenotypic transformation of vascular smooth muscle cells (VSMCs) to osteoblast-like cells, mediated by exosomes derived from calcified VSMCs and the exosomal microRNAs (miRNA) which may trigger some signals to recipient VSMCs. Bushen Huoxue (BSHX) formula has demonstrated its clinical efficacy in CKD and its protective role in CKD-VC rats has also been observed. However, little is known about its underlying mechanism.

Methods: To establish a VC model, aortic VSMCs from rats were induced to osteogenic differentiation by high-level phosphate (HP) in vitro. The expression of exosome and calcification makers were analyzed by western blot, including CD9, CD63, α-SMA, BMP-2, and Runx2, respectively. Differential expression of exosomal miRNAs in normal and HP-induced VSMCs were identified by using whole miRNA microarray technology. GO and KEGG analyses were performed to determine the significant enrichment of functions and signaling pathways in the target genes. In vivo, the CKD-VC rat model was established by administering adenine gavage combined with a high phosphorus diet. The rats were divided into normal control, model, low-dose BSHX, medium-dose BSHX, high-dose BSHX groups, and sevelamer groups. The blood biochemical parameters were measured. Renal histopathology and aortic calcification were observed. Western blot detected the levels of the calcification markers. Quantitative real-time PCR (qPCR) assay detected exosomal microRNA-32 (miR-32) mRNA expression in the aorta, the most differentially expressed exosomal miRNA previously identified. Phosphatase and tensin homolog located on chromosome ten (PTEN)/phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT) signaling pathway components were also tested by western blot.

Results: Exosomal miRNA-32 and PI3K/AKT signaling pathways were highly differentially expressed between normal and HP-induced VSMCs. In vivo, BSHX improved blood biochemical parameters, renal histopathology, and aortic calcification in CKD-VC rats. BSHX increased the expression level of α-SMA and decreased the level of BMP-2 and Runx2. BSHX also lowered the expression level of exosomal miR-32 mRNA, enhanced PTEN expression, therefore, reduced p-PI3K and p-AKT levels in the aorta.

Conclusion: BSHX alleviated VC in CKD rats by downregulating exosomal miR-32 expression in the aorta, thereby promoting PTEN expression and inhibiting the PI3K/AKT signaling pathway.