One of the major functions of autophagy through tightly controlled formation of autophagosomes is devoted to the removal of particles that escape degradation in conventional phagosomes. However, the present results indicate that both primary processes of phagocytosis selleck chem and autophagy in OBs are not followed by the degradation of internalized MSU microcrystals that remain intact inside persistent autop hagosomes. In addition, survival of OBs is not affected by MSU, but their proliferation is reduced. Our present results of the absence of MSU effect on OB mortality seems apparently in contradiction to a pre vious study that reported an inhibition of OB viability by MSU. However, major experimental differences be tween this report and the present study can explain this discrepancy.

The experiments presented here were performed with primary human OBs only, whereas Chhanas studies were carried out mostly with murine MC3T3 E1 cells, and Inhibitors,Modulators,Libraries the only viability data with human primary OBs of the published Inhibitors,Modulators,Libraries report used the MTT assay, which is, at best, an assay evalu ating cell proliferation and that requires controlling several important Inhibitors,Modulators,Libraries parameters, to be an indirect test Inhibitors,Modulators,Libraries of cell viability. Moreover, in the present study, we evaluate only PI incorporation by OBs, which repre sents a useful quantification Inhibitors,Modulators,Libraries of necrotic and late apoptotic cells. Interestingly, although OB prolif eration is reduced by MSU, their catabolic functions are activated because they are always alive after 7 days of culture.

The absence of degradation of MSU by these nonprofessional phagocytes was corroborated with the Dasatinib BMS-354825 findings of MSU directly encrusted in the ir regular matrix of gouty lesions of bone. Although visualization of MSU inside vacuoles was de layed for up to 24 hours, and NLRP3, which precedes the cleavage of LC3 I into LC3 II, appeared within 3 hours in MSU stimulated OB, intracellular signaling indicated a rapid activation of both autophagy and phagocytosis. Moreover, the process of phagocytosis ap peared an absolute necessity for subsequent autophagy of MSU, as shown by the absence of MSU autophagy secondarily to phagocytosis blockade. These sequences of phagocytosis followed by autophagy seem logical, be cause autophagy is aimed at destroying intracellular par ticles, whereas phagocytosis, also aimed at degrading foreign particles, is the process that will internalize extracellular particles. However, phagocytosis could have been sufficient to destroy MSU. Interestingly, MSU in the presence of OBs, nonprofessional phagocytes, can act as a danger signal and trigger the autophagy process through the rapid induction of NLRP3 to complete the degradation of MSU.