Repression of let-7b-5p prevents the development of multifidus muscle dysfunction by promoting vitamin D accumulation via upregulation of electron transfer flavoprotein alpha subunit in a rat model of multifidus muscle injury

Multifidus muscle dysfunction is associated with the multifidus muscle injury (MMI), which ultimately result in the low-back pain. Increasing evidence shows that microRNAs (miRs) may be involved in multifidus muscle dysfunction. In this study, we tested the hypothesis that downregulation of let-7b-5p may inhibit the multifidus muscle dysfunction development and progression. The target prediction program and luciferase activity determination confirmed electron transfer flavoprotein alpha subunit (ETFA) as a direct target gene of let-7b-5p. To study the mechanisms and functions of let-7b-5p in relation to ETFA in MMI progression, we prepared rats with experimental MMI, and a lentivirus-based packaging system was designed to upregulate expressions of let-7b-5p, and downregulate the expression of ETFA. ETFA was identified as a target gene of let-7b-5p. Older age, a longer duration of pain, and higher visual analog scale and Oswestry disability index scores for the patients with chronic low-back pain were linked to a more severe degree of degenerative muscle atrophy and fatty infiltration. Increased expression of let-7b-5p and decreased expression of ETFA and vitamin D receptor (VDR) were positively correlated with multifidus muscle dysfunction. Downregulated let-7b-5p could inhibit infiltration of collagen fibers, reverse the ultrastructural changes of multifidus muscle, and induce the VDR expression, thereby repair the MMI. The results provided a potential basis for let-7b-5p that could support targeted intervention in multifidus muscle dysfunction. Collectively, this study confirmed that downregulation of let-7b-5p has a potential inhibitory effect on the development of the function of the musculus myocytes by upregulating ETFA.