Emerging evidence suggests that dysregulated microRNAs (miRNAs) play a pivotal role in osteoarthritis (OA), but the role of specific miRNAs remains unclear. Accordingly, we identified OA-associated miRNAs and functional validation of results. Here, we demonstrate that miR-218-5p is significantly upregulated in moderate and severe OA and correlates with scores on a modified Mankin scale. Through gain-of-function and loss-of-function studies, miR-218-5p was shown to significantly affect matrix synthesis gene expression and chondrocyte proliferation and apoptosis. Using SW1353 and C28/I2 cells, PIK3C2A mRNA was identified as a target of miR-218-5p. Downregulation of miR-218-5p dramatically promoted expression of PIK3C2A and its downstream target proteins, such as Akt, mTOR, S6, and 4EBP1. More importantly, OA mice exposed to a miR-218-5p inhibitor were protected from cartilage degradation and had reduced proteoglycan loss and reduced loss of articular chondrocyte cellularity compared with control mice. miR-218-5p is a novel inducer of cartilage destruction via modulation of PI3K/Akt/mTOR signaling. Inhibition of endogenous miR-218-5p expression/activity appears to be an attractive approach to OA treatment.

Understanding the molecular mechanisms regulating the maintenance and destruction of intervertebral disc may lead to the development of new therapies for intervertebral disc degeneration (IDD). Here we present evidence from miRNA microarray analyses of clinical data sets along with in vitro and in vivo experiments that miR-141 is a key regulator of IDD. Gain- and loss-of-function studies show that miR-141 drives IDD by inducing nucleus pulposus (NP) apoptosis. Furthermore, miR-141 KO in mice attenuated spontaneous and surgically induced IDD. Mechanistically, miR-141 promotes IDD development by targeting and depleting SIRT1, a negative regulator of NF-κB pathway. Therapeutically, upregulation or downregulation of miR-141 by nanoparticle delivery in IDD model aggravated or alleviated experimental IDD, respectively. Our findings reveal a novel mechanism by which miR-141, in part, promotes IDD progression by interacting with SIRT1/NF-κB pathway. Blockade of miR-141 in vivo may serve as a potential therapeutic approach in the treatment of IDD.

Epidermolytic palmoplantar keratoderma (EPPK) is a relatively common autosomal-dominant skin disorder caused by mutations in the keratin 9 gene (KRT9), with few therapeutic options for the affected so far. Here, we report a knock-in transgenic mouse model that carried a small insertion-deletion (indel) mutant of Krt9, c.434delAinsGGCT (p.Tyr144delinsTrpLeu), corresponding to the human mutation KRT9/c.500delAinsGGCT (p.Tyr167delinsTrpLeu), which resulted in a human EPPK-like phenotype in the weight-stress areas of the fore- and hind-paws of both Krt9(+/mut) and Krt9(mut/mut) mice. The phenotype confirmed that EPPK is a dominant-negative condition, such that mice heterozygotic for the K9-mutant allele (Krt9(+/mut)) showed a clear EPPK-like phenotype. Then, we developed a mutant-specific short hairpin RNA (shRNA) therapy for EPPK mice. Mutant-specific shRNAs were systematically identified in vitro using a luciferase reporter gene assay and delivered into Krt9(+/mut) mice. shRNA-mediated knockdown of mutant protein resulted in almost normal morphology and functions of the skin, whereas the same shRNA had a negligible effect in wild-type K9 mice. Our results suggest that EPPK can be treated by gene therapy, and this has significant implications for future clinical application.