Expression of regucalcin in rat bone marrow cells: Involvement of osteoclastic bone resorption in regucalcin transgenic rats

The expression of regucalcin in rat bone marrow cells was investigated. The expression of regucalcin mRNA in the bone marrow cells of normal (wild-type) rat was shown by using reverse transcription-polymerase chain reaction (RT-PCR) with a specific primer of regucalcin cDNA. Regucalcin protein was detected in the marrow cells of normal (wild-type) rats using Western blot analysis. Regucalcin levels were significantly increased in the marrow cells of regucalcin transgenic (TG) male and female rats with increasing age (5-36 weeks old). When the marrow cells obtained from normal or regucalcin TG rats (36-week-old) were cultured for 7 days, the number of tartrate-resistant acid phosphatase (TRACP), a marker enzyme of osteoclasts, positive multinucleated cells (MNCs) were significantly increased in the marrow culture of regucalcin TG rats. This increase was remarkable in female TG rats as compared with male TG rats. The effect of parathyroid hormone [human PTH (1-34); 10−7 M] or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; 10−7 M] in stimulating TRACP-positive MNCs formation was significantly enhanced in female regucalcin TG rats. Calcium content in the femoral-diaphyseal and -meta-physeal tissues was significantly decreased in regucalcin TG rats (10- or 36-week-old). This decrease was greater in female than in male. Femoral-metaphyseal deoxyribonucleic acid (DNA) content was significantly reduced in regucalcin TG male and female rats (36-week-old). Moreover, serum inorganic phosphorus, triglyceride, HDL-cholesterol, and albumin concentrations were significantly increased in regucalcin TG female rats (36-week-old), while serum calcium, zinc, and glucose concentrations were not significantly altered in TG male and female rats. In TG male rats, serum triglyceride and HDL-cholesteral concentrations were significantly raised. This study demonstrates that regucalcin is expressed in rat bone marrow cells, and that osteoclastic bone resorption is stimulated in regucalcin TG rats with increasing age. Also, regucalcin TG aged rats was found to induce serum metabolic disorder.