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.

Objectives Despite preclinical studies involving miRNA therapeutics conducted in osteoarthritis (OA) over the years, none of these miRNAs have yet translated to clinical applications, owing largely to the lack of efficient intra-articular (IA) delivery systems. Here, we investigated therapeutic efficacy of the chondrocyte-specific aptamer-decorated PEGylated polyamidoamine nanoparticles (NPs)-based miRNAs delivery for OA. Methods The role of miR-141/200c cluster during skeletal and OA development was examined by miR-141/200c^flox/flox mice and Col2a1-CreER^T2; miR-141/200c^flox/flox mice. Histological analysis was performed in mouse joints and human cartilage specimens. Chondrocyte-specific aptamer-decorated NPs was designed, and its penetration, stability and safety were evaluated. OA progression was assessed by micro-CT analysis, X-ray and Osteoarthritis Research Society International scores after destabilising the medial meniscus surgery with miR-141/200c manipulation by NPs IA injection. Mass spectrometry analysis, molecular docking and molecular dynamics simulations were performed to investigate the interaction between aptamer and receptor. Results Increased retention of NPs inside joint space is observed. The NPs are freely and deeply penetrant to mice and human cartilage, and unexpectedly persist in chondrocytes for at least 5 weeks. OA chondrocytes microenviroment improves endo/lysosomal escape of microRNAs (miRNAs). Therapeutically, IA injection of miR-141/200c inhibitors provides strong chondroprotection, whereas ectopic expression of miR-141/200c exacerbates OA. Mechanistically, miR-141/200c promotes OA by targeting SIRT1, which acetylates histone in the promoters of interleukin 6 (IL-6), thereby activating IL-6/STAT3 pathway. Conclusions Our findings indicate that this nanocarrier can optimise the transport kinetics of miR-141/200c into chondrocytes, fostering miRNA-specific disease-modifying OA drugs development.

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.

Background: Although mesenchymal stem cells (MSCs) have been effective in tendinopathy, the mechanisms by which MSCs promote tendon healing have not been fully elucidated. In this study, we tested the hypothesis that MSCs transfer mitochondria to injured tenocytes in vitro and in vivo to protect against Achilles tendinopathy (AT). Methods: Bone marrow MSCs and H₂O₂-injured tenocytes were co-cultured, and mitochondrial transfer was visualized by MitoTracker dye staining. Mitochondrial function, including mitochondrial membrane potential, oxygen consumption rate, and adenosine triphosphate content, was quantified in sorted tenocytes. Tenocyte proliferation, apoptosis, oxidative stress, and inflammation were analyzed. Furthermore, a collagenase type I-induced rat AT model was used to detect mitochondrial transfer in tissues and evaluate Achilles tendon healing. Results: MSCs successfully donated healthy mitochondria to in vitro and in vivo damaged tenocytes. Interestingly, mitochondrial transfer was almost completely blocked by co-treatment with cytochalasin B. Transfer of MSC-derived mitochondria decreased apoptosis, promoted proliferation, and restored mitochondrial function in H₂O₂-induced tenocytes. A decrease in reactive oxygen species and pro-inflammatory cytokine levels (interleukin-6 and -1β) was observed. In vivo, mitochondrial transfer from MSCs improved the expression of tendon-specific markers (scleraxis, tenascin C, and tenomodulin) and decreased the infiltration of inflammatory cells into the tendon. In addition, the fibers of the tendon tissue were neatly arranged and the structure of the tendon was remodeled. Inhibition of mitochondrial transfer by cytochalasin B abrogated the therapeutic efficacy of MSCs in tenocytes and tendon tissues. Conclusions: MSCs rescued distressed tenocytes from apoptosis by transferring mitochondria. This provides evidence that mitochondrial transfer is one mechanism by which MSCs exert their therapeutic effects on damaged tenocytes.

Objectives: N⁶‐methyladenosine (m6A) is one of the most abundant internal RNA modifications. We investigated the role of m6A‐modified circRERE in osteoarthritis (OA) and its mechanism.Materials and Methods: CircRERE and IRF2BPL were screened by microarrays. The role of m6A‐modification in circRERE was examined by methylated RNA precipitation and morpholino oligo (MOs) treatment. The axis of circRERE/miR‐195‐5p/IRF2BPL/β‐catenin was determined using flow cytometry, western blotting and immunofluorescence in human chondrocytes (HCs) and corroborated using a mouse model of destabilization of medial meniscus (DMM) with intra‐articular (IA) injection of adeno‐associated viruses (AAV).Results: CircRERE was decreased in OA cartilage and chondrocytes compared with control. CircRERE downregulation was likely attributed to its increased m6A modification prone to endoribonucleolytic cleavage by YTHDF2‐HRSP12‐RNase P/MRP in OA chondrocytes. MOs transfection targeting HRSP12 binding motifs in circRERE partially reversed decreased circRERE expression and increased apoptosis in HCs treated with IL‐1β for 6 h. CircRERE exerted chondroprotective effects by targeting miR‐195‐5p/IRF2BPL, thus regulating the ubiquitination and degradation of β‐catenin. CircRere (mouse homologue) overexpression by IA‐injection of AAV‐circRere into mice attenuated the severity of DMM‐induced OA, whereas AAV‐miR‐195a‐5p or AAV‐sh‐Irf2bpl reduced the protective effects. The detrimental effects of AAV‐sh‐Irf2bpl on DMM‐induced OA were substantially counteracted by ICG‐001, an inhibitor of β‐catenin.Conclusions: Our study is a proof‐of‐concept demonstration for targeting m6A‐modified circRERE and its target miR‐195‐5p/IRF2BPL/β‐catenin as potential therapeutic strategies for OA treatment.

Scar tissue formation at the tendon-bone interface caused by excessive inflammation leads to insufficient healing strength, while the phagocytic clearance of dying cells (efferocytosis) has profound consequences on macrophage polarisation and the inflammatory response. Modulating the inflammatory microenvironment may have satisfactory curative effects in patients with anterior cruciate ligament reconstruction (ACLR). Bone marrow-derived macrophages (BMDMs) and polymorphonuclear leukocytes (PMNs) were harvested from bone marrow. The effects of milk fat globulin protein E8 (MFG-E8) on macrophage polarisation were compared with those of M1 and M2 macrophages induced by conventional methods. The BMDMs and apoptotic PMNs co-culture system was used to assess the efficiency of efferocytosis. The biological functions of MFG-E8 in tendon-bone healing by regulating macrophage efferocytosis and polarisation were further investigated using a rat ACLR model. BMDMs and PMNs were successfully isolated. Compared to conventional induction methods, MFG-E8 alone did not significantly induce macrophage M1 or M2 polarisation, but it could partially reverse the expression of inducible nitric oxide synthase (iNOS) in M1 macrophages. In vitro studies revealed that appropriate dosing of MFG-E8 could significantly promote the efficiency of macrophage efferocytosis and subsequently increase M2 polarisation. More importantly, significantly increased peri-tunnel new bone formation, tighter connected interface and better mechanical properties were observed after ACLR when treated with MFG-E8 in vivo. We further demonstrated that MFG-E8 remarkably facilitated the clearance of apoptotic cells and increased the number of M2 macrophages at the interface between the tendon graft and bone tunnel in the early postoperative stage. MFG-E8 promoted tendon-bone healing histologically and biomechanically, probably by the regulation of inflammatory processes via macrophage efferocytosis and M2 polarisation. The translational potential of this article: Regulation of macrophage efferocytosis and M2 polarization by MFG-E8 is expected to be a therapeutic strategy for promoting tendon-bone healing in patients undergoing ACLR.