Novel extraneural role of neurite outgrowth inhibitor A: modulation of osteoclastogenesis via positive feedback regulation of nuclear factor of activated T cell cytoplasmic 1

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

Postnatal expression and possible function of RANK and RANKL in the murine inner ear

The bone encasing the inner ear, known as the otic capsule, is unique because it remodels little postnatally compared to other bones in the body. Previous studies established that osteoprotegerin (OPG) in the inner ear inhibits otic capsule remodeling. OPG acts as a decoy receptor of receptor activator of nuclear factor κB ligand (RANKL) to disrupt the interaction between RANKL and RANK, the primary regulators of bone metabolism. Here we studied the expression and function of RANK and RANKL in the murine cochlea. Using a combination of in situ hybridization, real-time quantitative RT-PCR, and western blot, we demonstrate that Rankl and Rank genes and their protein products are expressed in the intracochlear soft tissues and the otic capsule in a developmentally regulated manner. Using a culture of neonatal murine cochlear neurons, we show that the interaction between RANK and RANKL inhibits neurite outgrowth in these neurons, and is associated with upregulation of NOGO-A expression. Taken together, our results suggest that, in addition to regulating otic capsule bone remodeling, RANK and RANKL expressed by intracochlear soft tissues may also regulate spiral ganglion neuron function by affecting neurite outgrowth.

A novel Bruton's tyrosine kinase inhibitor, acalabrutinib, suppresses osteoclast differentiation and Porphyromonas gingivalis lipopolysaccharide-induced alveolar bone resorption

BACKGROUND

Periodontitis is not only one of the most prevalent inflammatory diseases among adults, but also commonly linked to numerous systemic conditions including cardiovascular diseases, stroke, and diabetes. Although osteoclasts are responsible for the alveolar bone resorption during periodontitis pathogenesis, the development of pharmacologic strategies targeting these cells has not been vastly fruitful.

METHODS

Bone marrow macrophages were cultured in the presence of macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL) to examine the direct effect of acalabrutinib on osteoclastogenesis. Ca²⁺ oscillation and nuclear localization of NFATc1 in osteoclast precursors were examined to determine the precise molecular mechanism. LPS-induced alveolar bone loss model was employed for studying effect in in vivo bone resorption.

RESULTS

Acalabrutinib directly inhibited RANKL and LPS-induced in vitro osteoclast differentiation. In addition, acalabrutinib inhibited RANKL-induced phosphorylation of mitogen-activated protein kinases and reduced the expression of NF-κB. The inhibitory mechanism involved suppression of Ca²⁺ oscillation in osteoclast precursors resulting in the decreased NFATc1 expression and nuclear localization, which is a crucial prerequisite for osteoclastogenesis. The administration of acalabrutinib significantly reduced P. gingivalis lipopolysaccharide-induced alveolar bone erosion in mice.

CONCLUSION

These data indicate that acalabrutinib is an effective inhibitor of osteoclastogenesis both in vitro and in vivo, with a potential for a novel strategy against bone destruction by periodontitis.

Compartmentalized Microfluidic Platforms: The Unrivaled Breakthrough of In Vitro Tools for Neurobiological Research

Microfluidic technology has become a valuable tool to the scientific community, allowing researchers to study fine cellular mechanisms with higher variable control compared with conventional systems. It has evolved tremendously, and its applicability and flexibility made its usage grow exponentially and transversely to several research fields. This has been particularly noticeable in neuroscience research, where microfluidic platforms made it possible to address specific questions extending from axonal guidance, synapse formation, or axonal transport to the development of 3D models of the CNS to allow pharmacological testing and drug screening. Furthermore, the continuous upgrade of microfluidic platforms has allowed a deeper study of the communication occurring between different neuronal and glial cells or between neurons and other peripheral tissues, both in physiological and pathological conditions. Importantly, the evolution of microfluidic technology has always been accompanied by the development of new computational tools addressing data acquisition, analysis, and modeling.

Sex-Specific Protection of Osteoarthritis by Deleting Cartilage Acid Protein 1

Cartilage acidic protein 1 (CRTAC1) was recently identified as an elevated protein in the synovial fluid of patients with osteoarthritis (OA) by a proteomic analysis. This gene is also upregulated in both human and mouse OA by transcriptomic analysis. The objective of this study was to characterize the expression and function of CRTAC1 in OA. Here, we first confirm the increase of CRTAC1 in cartilage biopsies from OA patients undergoing joint replacement by real-time PCR and immunohistochemistry. Furthermore, we report that proinflammatory cytokines interleukin-1beta and tumor necrosis factor alpha upregulate CRTAC1 expression in primary human articular chondrocytes and synovial fibroblasts. Genetic deletion of Crtac1 in mice significantly inhibited cartilage degradation, osteophyte formation and gait abnormalities of post-traumatic OA in female, but not male, animals undergoing the destabilization of medial meniscus (DMM) surgery. Taken together, CRTAC1 is upregulated in the osteoarthritic joint and directly induced in chondrocytes and synovial fibroblasts by pro-inflammatory cytokines. This molecule is necessary for the progression of OA in female mice after DMM surgery and thus represents a potential therapy for this prevalent disease, especially for women who demonstrate higher rates and more severe OA.

MicroRNA-124 regulates osteoclast differentiation

Osteoclasts are specialized cells for bone-resorption originated from precursors of macrophage/monocyte lineage. The receptor activator of NFκB ligand (RANKL) initiates osteoclast differentiation, in which nuclear factor of activated T cell cytoplasmic 1 (NFATc1) plays a key role as a master transcription factor. In the present report, we show that microRNA-124 (miR-124) regulates osteoclastogenesis of mouse bone marrow macrophages (BMMs) by suppressing NFATc1 expression. On the other hand, synthetic inhibitor that binds specifically to miR-124 enhanced osteoclast differentiation and NFATc1 expression. The overexpression of a constitutively active form of NFATc1 prevented the inhibitory effect of miR-124 on osteoclastogenesis. Finally, miR-124 also affected the proliferation and motility of osteoclast precursors, the latter coinciding with the reduced expression of RhoA and Rac1. These findings not only reveal unprecedented role of miR-124 in osteoclastogenesis but also suggest a novel mode of regulation of NFATc1 in osteoclasts.

Plasma membrane calcium ATPase regulates bone mass by fine-tuning osteoclast differentiation and survival

Plasma membrane calcium ATPases PMCA1 and PMCA4 regulate osteoclast differentiation and survival by regulating NFATc1 and NO.

The precise regulation of Ca²⁺ dynamics is crucial for proper differentiation and function of osteoclasts. Here we show the involvement of plasma membrane Ca²⁺ ATPase (PMCA) isoforms 1 and 4 in osteoclastogenesis. In immature/undifferentiated cells, PMCAs inhibited receptor activator of NF-κB ligand–induced Ca²⁺ oscillations and osteoclast differentiation in vitro. Interestingly, nuclear factor of activated T cell c1 (NFATc1) directly stimulated PMCA transcription, whereas the PMCA-mediated Ca²⁺ efflux prevented NFATc1 activation, forming a negative regulatory loop. PMCA4 also had an anti-osteoclastogenic effect by reducing NO, which facilitates preosteoclast fusion. In addition to their role in immature cells, increased expression of PMCAs in mature osteoclasts prevented osteoclast apoptosis both in vitro and in vivo. Mice heterozygous for PMCA1 or null for PMCA4 showed an osteopenic phenotype with more osteoclasts on bone surface. Furthermore, PMCA4 expression levels correlated with peak bone mass in premenopausal women. Thus, our results suggest that PMCAs play important roles for the regulation of bone homeostasis in both mice and humans by modulating Ca²⁺ signaling in osteoclasts.