RANKL (receptor activator of NF-B ligand) induces osteoclastogenesis by activating multiple signaling pathways in osteoclast precursor cells, chief among which is induction of long lasting oscillations in the intracellular concentration ofBone is a dynamic tissue that is constantly being remodeled. The remodeling process is a delicate balance between the activities of osteoblasts and osteoclasts. Interference with this balance results in serious human pathologies that affect bone integrity. Tipping the balance in favor of osteoclasts leads to pathological bone resorption, which is observed in autoimmune arthritis, osteoporosis, and periodontitis (1, 2).Bone marrow-derived monocyte/macrophage precursor cells (BMM) 2 of a hematopoietic origin develop into osteoclasts through cell-to-cell signaling with mesenchymal cells, such as osteoblasts (3, 4). Cell-to-cell interaction between the osteoclast precursors and osteoblastic/stromal cells are also essential for the differentiation of osteoclast progenitor cells into mature osteoclasts (5, 6). RANKL (receptor activator of NF-B ligand) is expressed in osteoblastic/stromal cells and is vital for osteoclast differentiation (7-11). Stimulation of the RANK receptor by RANKL in the presence of the macrophage colonystimulating factor (M-CSF) causes osteoclast differentiation and activation in vitro (6,8,12). Moreover, the binding of RANKL to its receptor results in the recruitment of the TNF receptor-associated factor (TRAF) family of proteins, e.g. TRAF6, which are linked to the NF-B and JNK pathways (13-15). Of particular importance, a series of signals following RANK activation induce oscillations in the free intracellular concentration of Ca 2ϩ ([Ca 2ϩ ] i ), which trigger the late stage of osteoclast differentiation by activating the nuclear factor of activated T cells type c1 (NFATc1) (16). Unique aspects of these RANKL-stimulated Ca 2ϩ oscillations is that they are observed only 24 -48 h post-stimulation, indicating the need for induction of the pathway responsible for the Ca 2ϩ oscillations. The nature of this pathway and how it is induced are not known. Ca 2ϩ is a ubiquitous intracellular messenger that mediates a wide variety of cellular functions and is involved in the fundamental cellular processes of proliferation, differentiation, and programmed cell death (17). In the case of osteoclast differentiation, Ca 2ϩ plays an important role by sequentially activating calcineurin and NFATc1 (16). Members of the NFAT family are among the most strongly induced transcription factors following RANKL stimulation. During osteoclastogenesis, costimulatory signals mediated by the immunoreceptor tyrosine-based

The gut microbiome participates in numerous physiologic functions and communicates intimately with the host immune system. Antimicrobial peptides are critical components of intestinal innate immunity. We report a prominent role for antimicrobials secreted by pancreatic acinari in shaping the gut microbiome that is essential for intestinal innate immunity, barrier function, and survival. Deletion of the Ca2+ channel Orai1 in pancreatic acini of adult mice resulted in 60–70% mortality within three weeks. Despite robust activation of the intestinal innate immune response, mice lacking acinar Orai1 exhibited intestinal bacterial outgrowth and dysbiosis, ultimately causing systemic translocation, inflammation, and death. While digestive enzyme supplementation was ineffective, treatments constraining bacterial outgrowth (purified liquid diet, broad-spectrum antibiotics), rescued survival, feeding, and weight gain. Pancreatic levels of cathelicidin-related antimicrobial peptide (CRAMP) were reduced, and supplement of synthetic CRAMP prevented intestinal disease. These findings reveal a critical role for antimicrobial pancreatic secretion in gut innate immunity.

Odontoblasts function as mechanosensory receptors because of the expression of mechanosensitive channels in these cells. However, it is unclear if odontoblasts direct the signal transmission evoked by heat/cold or osmotic changes. This study investigated the effects of heat/cold or osmotic changes on calcium signaling and the functional expression of the thermo/mechanosensitive transient receptor potential (TRP) channels in primary cultured mouse odontoblastic cells, with the use of RT-PCR, fluorometric calcium imaging, and electrophysiology. TRPV1, TRPV2, TRPV3, TRPV4, and TRPM3 mRNA was expressed, but TRPM8 and TRPA1 mRNA was not. The receptor-specific stimulation of TRPV1-3 (heat-sensing receptors) and TRPV4/ TRPM3 (mechanic receptors) caused increases in the intracellular calcium concentration. Moreover, the channel activities of TRPV1-4 and TRPM3 were confirmed by a whole-cell patch-clamp technique. These results suggest that primary cultured mouse odontoblasts express heat/mechanosensitive TRP channels and play a role in the underlying mechanisms of thermo/mechanosensitive sensory transmission.