Leptin receptors and beta2-adrenergic receptor mRNA expression in brain injury-related heterotopic ossification

Heterotopic ossification (HO) frequently occurs after brain injury. Recently, we found that leptin levels were decreased in the serum of patients with HO. Data suggest two mechanisms mediating leptin effects: a central suppressive mechanism acting via the beta(2)-adrenergic system and a direct stimulatory action starting when leptin binds to its receptors in osteoblastic cells. In this study, we analyzed leptin and beta(2)-adrenergic receptors mRNA expression in osteocytes originated from normal or heterotopic bone biopsies to investigate whether direct or indirect pathway signaling might be implicated in this pathological bone formation. We report for the first time the mRNA expression of the leptin receptor isoforms in osteocytes isolated from all biopsies. Moreover, quantitative reverse transcription-polymerase chain reaction allowed us to measure a significant decrease in the level of beta(2)-adrenergic receptor mRNA in cells isolated from heterotopic bone biopsies. These results could suggest an association between hypothalamic leptin signaling and brain injury-related HO.