Both long non-coding RNA (lncRNA) RMRP and heat shock protein (HSP) 70 have been known to play crucial roles in inflammation. The present study investigated the roles of lncRNA RMRP and HSP70 protein 4 (HSPA4) in lipopolysaccharide (LPS)-induced sepsis. The C57BL/6 mice were treated with LPS, following which the cardiomyocytes were isolated for in vitro experiments. Further, a cardiac muscle cell line, HL-1 was transfected with plasmids expressing RMRP and HSPA4, si-NC, si-HSPA4, miR-1-5p mimic, and controls in vitro. Cell apoptosis, mitochondrial membrane potential (MMP), and levels of intracellular reactive oxygen species (ROS), mRNAs, and proteins were detected in the transfected mice tissues and cells. The LPS treatment significantly reduced the expression levels of RMRP, MMP, and mitochondrial cytochrome C. Moreover, it enhanced the cardiomyocyte apoptosis, intracellular ROS levels, cytoplasm cytochrome C levels, and the expression of caspase-3 and caspase-9 and nuclear factor κB (NF-κB) p65 subunit. The predicted RMRP-miR-1-5p-HSPA4 network was validated by co-transfection experiments in vitro in HL-1 cells. The transfection of miR-1-5p-treated cells with pcDNA-RMRP enhanced the levels of the protein HSPA4; however, no change at the mRNA level was observed. Moreover, miR-1-5p mimic attenuated the protective effect of pcDNA-HSPA4 against LPS-induced mitochondrial damage and apoptosis. In addition, we observed that silencing of HSPA4 increased the expression of nuclear p65; however, this effect could be reversed by co-transfection with pcDNA-RMRP. The lncRNA RMRP axis acts as a sponge for miR-1-5p. RMRP inhibits LPS-induced apoptosis of cardiomyocytes and mitochondrial damage by suppressing the post-transcriptional regulatory function of miR-1-5p on HSPA4. We believe that RMRP exhibits therapeutic potential for LPS-induced myocardial dysfunction both in vitro and in vivo.
Keywords: HSPA4; cardiomyocyte; lncRNA RMRP; miR-1-5p; sepsis.