MLO-Y4 cells, courtesy of Dr. Lynda Bonewald were maintained in growth medium (α-MEM (Invitrogen)+5% fetal bovine serum (FBS, Atlanta Biologicals)+5% bovine calf serum (HyClone)+1% Penicillin/Streptomycin). Primary osteocytes were isolated from serial digestion of 8 week old wildtype C57BL/6 mouse long bones as we previously reported (16 (link)) and were maintained in growth medium as described above. OCY454 cells, courtesy of Dr. Paola Divieti-Pajevic, were maintained in growth medium (α-MEM+10% FBS+1% Antibiotic/antimycotic (Gibco)) and handled according to published protocols (17 (link)). Briefly, OCY454 cells were maintained at 33°C on collagen coated plates, and differentiated at 37°C on non-coated plates for 2 weeks prior to the onset of experiments to promote an osteocytic phenotype, according to the recommended protocol for these cells.