Expression and Functional Role of TRPV4 in Bone Marrow-Derived CD11c(+) Cells

The increase in cytosolic Ca(2+) is essential in key effector functions of dendritic cells (DCs), including differentiation, maturation, cytokine expression, and phagocytosis. Although several Ca(2+)-permeable ion channels have been described in DCs, the contribution of transient receptor potential (TRP) channels remains poorly understood. Here, we investigated whether TRPV4 plays a role in the differentiation, maturation, and phagocytosis of granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced mouse bone marrow-derived cells (BMDCs). Using intracellular Ca(2+) imaging experiments, we found that TRPV4 was functionally expressed in the plasma membrane of immature CD11c(+) BMDCs and that its activity and expression were downregulated in CD11c(+) BMDCs matured with lipopolysaccharide (LPS). Comparative analysis of the GM-CSF-stimulated cells showed that Trpv4 knockout and wild-type bone marrow cultures had a similar distribution of differentiated cells, generating a heterogenous culture population rich in CD11c(+), CD11b(+) cells, and low levels of F4/80(+) cells. The lack of TRPV4 did not prevent the LPS-induced nuclear translocation of NF-κB, the upregulation of the proinflammatory cytokines IL-6 and IL-12, or the upregulation of the maturation markers CD40, CD80, and CD86. In contrast, TRPV4-deficient CD11c(+) BMDCs exhibited a significantly reduced endocytic capacity of IgG-coated beads, but the internalization of uncoated beads in the absence of TRPV4 was not affected. Taken together, our results demonstrate that TRPV4 was dispensable in the differentiation and maturation of mouse CD11c(+) BMDCs but contributed to the mechanism underlying Fc receptor-mediated phagocytosis. Overall, our results further strengthen the role of TRPV4 in immune-related processes.