Novel targets for the prevention of osteoporosis - lessons learned from studies of metabolic bone disorders

Regulation of pain neurotransmitters and chondrocytes metabolism mediated by voltage-gated ion channels: A narrative review

Osteoarthritis (OA) is one of the leading causes of chronic pain and dysfunction. It is essential to comprehend the nature of pain and cartilage degeneration and its influencing factors on OA treatment. Voltage-gated ion channels (VGICs) are essential in chondrocytes and extracellular matrix (ECM) metabolism and regulate the pain neurotransmitters between the cartilage and the central nervous system. This narrative review focused primarily on the effects of VGICs regulating pain neurotransmitters and chondrocytes metabolism, and most studies have focused on voltage-sensitive calcium channels (VSCCs), voltage-gated sodium channels (VGSCs), acid-sensing ion channels (ASICs), voltage-gated potassium channels (VGKCs), voltage-gated chloride channels (VGCCs). Various ion channels coordinate to maintain the intracellular environment's homeostasis and jointly regulate metabolic and pain under normal circumstances. In the OA model, the ion channel transport of chondrocytes is abnormal, and calcium influx is increased, which leads to increased neuronal excitability. The changes in ion channels are strongly associated with the OA disease process and individual OA risk factors. Future studies should explore how VGICs affect the metabolism of chondrocytes and their surrounding tissues, which will help clinicians and pharmacists to develop more effective targeted drugs to alleviate the progression of OA disease.

MiR-655-3p inhibits the progression of osteoporosis by targeting LSD1 and activating BMP-2/Smad signaling pathway

Osteoporosis (OP) is one of the most common chronic metabolic bone diseases in the seniors and postmenopausal women. Plenty of microRNAs (miRNAs) have been confirmed to be involved in OP progression. However, the role of miR-655-3p in osteogenic differentiation and bone formation was still unclear. In this study, we aimed to investigate the cellular function of miR-655-3p and its underlying mechanism in OP. We found that miR-655-3p expression was downregulated in both ovariectomized (OVX) mice bone tissues and MC3T3-E1 cells treated with simulated microgravity (MG). MiR-655-3p overexpression facilitated cell differentiation but suppressed cell apoptosis of MC3T3-E1 cells induced by simulated MG. Mechanistically, we confirmed that lysine-specific histone demethylase 1 (LSD1) is a downstream target gene of miR-655-3p. Furthermore, overexpression of miR-655-3p activated the bone morphogenetic protein 2 (BMP-2)/decapentaplegic homolog (Smad) signaling pathway by suppressing LSD1 expression. Moreover, LSD1 knockdown accelerated osteogenic differentiation and inhibited apoptosis in MC3T3-E1 cells under simulated MG. Additionally, the OVX mouse model was established to investigate the role of miR-655-3p/LSD1 axis in vivo. The results demonstrated that LSD1 could reverse the effects triggered by the injection of adeno-associated virus-miR-655-3p on OP development. Further investigations revealed that miR-655-3p boosted osteogenic differentiation through LSD1/BMP-2/Smad signaling pathway. In summary, these findings implied a potential value of miR-655-3p in OP therapy.

G protein-coupled receptors as anabolic drug targets in osteoporosis

Osteoporosis is a progressive bone disorder characterised by imbalance between bone building (anabolism) and resorption (catabolism). Most therapeutics target inhibition of osteoclast-mediated bone resorption, but more recent attention in early drug discovery has focussed on anabolic targets in osteoblasts or their precursors. Two marketed agents that display anabolic properties, strontium ranelate and teriparatide, mediate their actions via the G protein-coupled calcium-sensing and parathyroid hormone-1 receptors, respectively. This review explores their activity, the potential for improved therapeutics targeting these receptors and other putative anabolic GPCR targets, including Smoothened, Wnt/Frizzled, relaxin family peptide, adenosine, cannabinoid, prostaglandin and sphingosine-1-phosphate receptors.

Identification of biallelic LRRK1 mutations in osteosclerotic metaphyseal dysplasia and evidence for locus heterogeneity

BACKGROUND

Osteosclerotic metaphyseal dysplasia (OSMD) is a unique form of osteopetrosis characterised by severe osteosclerosis localised to the bone ends. The mode of inheritance is autosomal recessive. Its genetic basis is not known.

OBJECTIVE

To identify the disease gene for OSMD.

METHODS AND RESULTS

By whole exome sequencing in a boy with OSMD, we identified a homozygous 7 bp deletion (c.5938_5944delGAGTGGT) in the LRRK1 gene. His skeletal phenotype recapitulated that seen in the Lrrk1-deficient mouse. The shared skeletal hallmarks included severe sclerosis in the undermodelled metaphyses and epiphyseal margins of the tubular bones, costal ends, vertebral endplates and margins of the flat bones. The deletion is predicted to result in an elongated LRRK1 protein (p.E1980Afs*66) that lacks a part of its WD40 domains. In vitro functional studies using osteoclasts from Lrrk1-deficient mice showed that the deletion was a loss of function mutation. Genetic analysis of LRRK1 in two unrelated patients with OSMD suggested that OSMD is a genetically heterogeneous condition.

CONCLUSIONS

This is the first study to identify the causative gene of OSMD. Our study provides evidence that LRRK1 plays a critical role in the regulation of bone mass in humans.