Expression of precerebellins in cultured rat calvaria osteoblast-like cells

Cerebellin (CER), originally isolated from rat cerebellum, is a hexadecapeptide derived from the larger precursor called precerebellin 1 (Cbln1). At present 4 propeptides designated as Cbln1, Cbln2, Cbln3 and Cbln4 are recognized. They belong to precerebellin subfamily of the C1q family proteins. Precerebellins act as transneuronal regulators of synapse development and synaptic plasticity in various brain regions. Initially CER was thought to be a cerebellum specific peptide, however subsequent studies revealed its presence in other brain regions as well as in extraneuronal tissues. We investigated whether precerebellins are expressed and involved in regulation of cultured rat calvarial osteoblast-like (ROB) cells. Classic RT-PCR revealed the presence of Cbln1 and Cbln3 mRNA in fragments of rat calvaria, in freshly isolated ROB cells and in ROB cells cultured for 7, 14 and 21 days. Cbln2 and Cbln4 mRNA, on the other hand, could not be demonstrated in ROB cells but was found to be present in the brain. In freshly isolated ROB cells expression of Cbln1 gene was very low and gradually increased in relation to the duration of culture. Expression of Cbln3, on the other hand, was very low in fragments of rat calvaria, and increased notably after digestion with collagenase-I. The highest expression of this precerebellin was observed at day 14 of culture while at days 7 and 21 levels of expressions were notably lower. Neither Cbln2 nor Cbln4 was found to be expressed in the ROB cells. Neither CER nor des-Ser1-CER (10−10-10−6M) affect osteocalcin production and proliferation rate of studied cells. The above findings suggest that CER, which theoretically would be derived from Cbln1, modulate neither differentiated (osteocalcin secretion) nor basic (proliferation) functions of cultured rat osteoblast-like cells. The obtained data raise an intriguing hypothesis that precerebellins may be involved in regulating of spatial organization of osteoblastic niches in the bone.