Expression and localization of Phosphoinositide-specific Phospholipases C in cultured, differentiating and stimulated human osteoblasts

The osteoblasts contribute to bone homeostasis maintaining the bone mass, and intervene in bone injuries repair. The limited number of available therapeutic agents promoting osteogenesis aroused the greatest interest in the control of osteoblasts’ activity. Insights in the events leading to the proliferation and differentiation of osteoblasts might allow uncover potential molecular targets to control the complex mechanisms underlying bone remodeling. Oscillations of calcium act crucially during this remodeling, affecting both the differentiation and proliferation of osteoblasts. Signal transduction pathways contribute to the differentiation and metabolic activities of osteoblasts, with special regard to calcium-related signaling, including the Phosphoinositide (PI) pathway and related Phospholipases C (PLCs). In order to evaluate the role of PLC enzymes’ family in human osteoblasts (HOBs), we analyzed the expression of PLC genes and the localization of PLC enzymes in cultured HOBs and in in vitro differentiating HOBs after 3, 10, 17 and 23 days, and in HOBs stimulated with Lipopolysaccharide, which affects the differentiation of osteoblasts, after 3, 6, 24 and 48 hours. Our results confirm the transcription of most PLC genes and the presence of a number of PLC enzymes in HOBs, differently localized in the nucleus, in the cytoplasm or both, as well as in cell protrusions. The localization of PLC enzymes within the cell suggests the activation of both the PI nuclear and of the cytoplasmic cycle in HOBs. Depending on the experimental conditions, transcripts of splicing variants of selected PLC genes were detected and the localization of most PLC enzymes varied, with special regard to enzymes belonging to the PLC ,  and  sub-families. Further studies addressed to elucidate the complex network involving the signal transduction of PLCs might provide further insights into the complex signal transduction network in bone remodeling, also offering the opportunity to identify promising molecular targets.