Targeted inhibition of phospholipase C γ2 adaptor function blocks osteoclastogenesis and protects from pathological osteolysis

Genes and Pathways Associated with Skeletal Sagittal Malocclusions: A Systematic Review

Skeletal class II and III malocclusions are craniofacial disorders that negatively impact people’s quality of life worldwide. Unfortunately, the growth patterns of skeletal malocclusions and their clinical correction prognoses are difficult to predict largely due to lack of knowledge of their precise etiology. Inspired by the strong inheritance pattern of a specific type of skeletal malocclusion, previous genome-wide association studies (GWAS) were reanalyzed, resulting in the identification of 19 skeletal class II malocclusion-associated and 53 skeletal class III malocclusion-associated genes. Functional enrichment of these genes created a signal pathway atlas in which most of the genes were associated with bone and cartilage growth and development, as expected, while some were characterized by functions related to skeletal muscle maturation and construction. Interestingly, several genes and enriched pathways are involved in both skeletal class II and III malocclusions, indicating the key regulatory effects of these genes and pathways in craniofacial development. There is no doubt that further investigation is necessary to validate these recognized genes’ and pathways’ specific function(s) related to maxillary and mandibular development. In summary, this systematic review provides initial insight on developing novel gene-based treatment strategies for skeletal malocclusions and paves the path for precision medicine where dental care providers can make an accurate prediction of the craniofacial growth of an individual patient based on his/her genetic profile.

Phospholipase Cγ in Toll-like receptor-mediated inflammation and innate immunity

Among the phospholipase C (PLC) isoforms, PLCγ not only has unique structural characteristics in terms of harboring SH2 and SH3 domains but also mediates growth factor-induced signaling pathways. PLCγ isoforms are expressed in several innate immune cell types, including macrophages, natural killer cells, mast cells, and neutrophils. Stimulation of Fc receptor or integrin in innate immune cells induces PLCγ activation, which leads to phosphoinositide hydrolysis and calcium increase. The products of PLCγ activity mediate the innate immune response by regulating respiratory burst, phagocytosis, cell adhesion, and cell migration. PLCγ also regulates the inflammatory response by affecting Toll-like receptor-mediated signaling. Here, we briefly review the current understanding of the functional role of PLCγ in inflammation and innate immunity in some innate immune cell types.

Osteoprotegerin Regulates Pancreatic β-Cell Homeostasis upon Microbial Invasion

Osteoprotegerin (OPG), a decoy receptor for receptor activator of NF-κB ligand (RANKL), antagonizes RANKL’s osteoclastogenic function in bone. We previously demonstrated that systemic administration of lipopolysaccharide (LPS) to mice elevates OPG levels and reduces RANKL levels in peripheral blood. Here, we show that mice infected with Salmonella, Staphylococcus, Mycobacteria or influenza virus also show elevated serum OPG levels. We then asked whether OPG upregulation following microbial invasion had an effect outside of bone. To do so, we treated mice with LPS and observed OPG production in pancreas, especially in β-cells of pancreatic islets. Insulin release following LPS administration was enhanced in mice lacking OPG, suggesting that OPG inhibits insulin secretion under acute inflammatory conditions. Consistently, treatment of MIN6 pancreatic β-cells with OPG decreased their insulin secretion following glucose stimulation in the presence of LPS. Finally, our findings suggest that LPS-induced OPG upregulation is mediated in part by activator protein (AP)-1 family transcription factors, particularly Fos proteins. Overall, we report that acute microbial infection elevates serum OPG, which maintains β-cell homeostasis by restricting glucose-stimulated insulin secretion, possibly preventing microbe-induced exhaustion of β-cell secretory capacity.

Tmem178 acts in a novel negative feedback loop targeting NFATc1 to regulate bone mass

Phospholipase C gamma-2 (PLCγ2)-dependent calcium (Ca(2+)) oscillations are indispensable for nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) activation and downstream gene transcription driving osteoclastogenesis during skeletal remodeling and pathological bone loss. Here we describe, to our knowledge, the first known function of transmembrane protein 178 (Tmem178), a PLCγ2 downstream target gene, as a critical modulator of the NFATc1 axis. In surprising contrast to the osteopetrotic phenotype of PLCγ2(-/-) mice, Tmem178(-/-) mice are osteopenic in basal conditions and are more susceptible to inflammatory bone loss, owing to enhanced osteoclast formation. Mechanistically, Tmem178 localizes to the ER membrane and regulates RANKL-induced Ca(2+) fluxes, thus controlling NFATc1 induction. Importantly, down-regulation of Tmem178 is observed in human CD14(+) monocytes exposed to plasma from systemic juvenile idiopathic arthritis patients. Similar to the mouse model, reduced Tmem178 expression in human cells correlates with excessive osteoclastogenesis. In sum, these findings identify an essential role for Tmem178 to maintain skeletal mass and limit pathological bone loss.

Inhibiting the Recruitment of PLCγ1 to Kaposi's Sarcoma Herpesvirus K15 Protein Reduces the Invasiveness and Angiogenesis of Infected Endothelial Cells

Kaposi’s sarcoma (KS), caused by Kaposi’s sarcoma herpesvirus (KSHV), is a highly vascularised tumour of endothelial origin. KSHV infected endothelial cells show increased invasiveness and angiogenesis. Here, we report that the KSHV K15 protein, which we showed previously to contribute to KSHV-induced angiogenesis, is also involved in KSHV-mediated invasiveness in a PLCγ1-dependent manner. We identified βPIX, GIT1 and cdc42, downstream effectors of PLCγ1 in cell migration, as K15 interacting partners and as contributors to KSHV-triggered invasiveness. We mapped the interaction between PLCγ1, PLCγ2 and their individual domains with two K15 alleles, P and M. We found that the PLCγ2 cSH2 domain, by binding to K15P, can be used as dominant negative inhibitor of the K15P-PLCγ1 interaction, K15P-dependent PLCγ1 phosphorylation, NFAT-dependent promoter activation and the increased invasiveness and angiogenic properties of KSHV infected endothelial cells. We increased the binding of the PLCγ2 cSH2 domain for K15P by substituting two amino acids, thereby creating an improved dominant negative inhibitor of the K15P-dependent PLCγ1 activation. Taken together, these results demonstrate a necessary role of K15 in the increased invasiveness and angiogenesis of KSHV infected endothelial cells and suggest the K15-PLCγ1 interaction as a possible new target for inhibiting the angiogenic and invasive properties of KSHV.

Kaposi’s Sarcoma (KS), etiologically linked to Kaposi’s sarcoma herpesvirus (KSHV), is a tumour of endothelial origin characterised by angiogenesis and invasiveness. In vitro, KSHV infected endothelial cells display an increased invasiveness and high angiogenicity. Here we report that the KSHV protein K15, which increases the angiogenicity of endothelial cells, contributes to KSHV-mediated invasiveness by the recruitment and activation of the cellular protein PLCγ1 and its downstream effectors βPIX, GIT1 and cdc42. We explored the functional consequences of disrupting the K15-PLCγ1 interaction by using an isolated PLCγ2 cSH2 domain as a dominant negative inhibitor. This protein fragment, by interacting with K15, reduces K15-driven recruitment and activation of PLCγ1 in a dose-dependent manner. Moreover, the PCLγ2 cSH2 domain, when overexpressed in KSHV infected endothelial cells, reduces the angiogenesis and invasiveness induced by the virus. These findings highlight the role of the K15-PLCγ1 interaction in KSHV-mediated invasiveness and identify it as a possible therapeutic target.