gms | German Medical Science

Objectives: Coxarthrosis (CA) and osteoporosis (OP) are two common musculoskeletal disorders, closely associated with aging, morbidity and disability but with different pathophysiological aspects and symptoms. The relation between these conditions is still unclear but in accordance that CA is regarded as disease of the whole joint, both, CA and OP affect bone. There is clear evidence that the sensory and sympathetic nervous system modulate bone metabolism via their neurotransmitters and may even promote structural bone changes in musculoskeletal disorders. This study investigates trabecular bone parameters as well as vitality, activity and gene expression profile of neurotransmitter receptors neurokinin 1 (tacr1), calcitonin receptor-like receptor (calcrl) and adrenergic receptor β2 (adrb2) in femoral osteoblasts from patients with fracture and osteoporosis alone (FX/OP) or coxarthrosis combined with osteoporosis (CA/OP).

Methods: Osteoblast-like cells were isolated of bone chips obtained from patients with fracture and osteoporosis (FX/OP) or coxarthrosis combined with osteoporosis (CA/OP) after hip replacement surgery. Cells were cultured in osteogenic medium for 14, 21, 28 and 35 days. Viability (WST-1 reagent), ALP activity and alizarin red stained areas were analyzed. Gene expression of tacr1, calcrl and adrb2 was analyzed by quantitative RT-PCR. Bone parameters (BV/TV, Tb.N., Tb.Th., Tb.Sp.) of trabecular bone samples were analyzed via µCt scanning.

Results and conclusion: Vitality and ALP activity of osteoblasts from FX/OP patients increased significantly from day 14 to 35 whereas no significant increase was detected for osteoblasts from CA/OP patients. Osteoblasts from FX/OP patients showed no significant difference in calcium deposition ability over time whereas the amount of extracellular calcium increased significantly for osteoblasts from CA/OP patients from day 14 to 35. With respect to neurotransmitter receptor gene expression, adrb2 gene expression was higher in FX/OP osteoblasts at day 14 of osteogenic differentiation compared to CA/OP osteoblasts. During osteogenic differentiation, gene expression of adrb2 declined in both, osteoblasts from FX/OP and CA/OP patients. We found no differences regarding calcrl gene expression but gene expression of tacr1 was by trend higher after 35 days of osteogenic differentiation in FX/OP osteoblasts with no differences in CA/OP osteoblasts. µCT analysis revealed reduced BV/TV ratio, reduced trabecular number and higher trabecular separation in bone samples from CA/OP patients compared to FX/OP patients.

We assume that disease phenotype differently affects metabolism and calcium deposition ability during osteogenic differentiation of osteoblasts from CA/OP compared to FX/OP patients resulting in inferior trabecular bone structure in trabecular bone of CA/OP patients. Differences in neurotransmitter receptor gene expression might influence osteoblast metabolism thereby possibly contributing to differences in bone structure.