gms | German Medical Science

Objectives: In previous studies we observed reduced biomechanical bone strength and matrix integrity in mice lacking the sensory neurotransmitter substance P (SP) [1]. A similar effect on bone microarchitecture has been described for α-calcitonin gene-related peptide (α-CGRP)-deficient mice [2]. Previously, we observed alterations in cell survival and differentiation capacity of osteoblasts and osteoclasts isolated from wildtype mice when stimulated with SP and α-CGRP. We assume that changes in sensory neurotransmitter balance modulate bone cell metabolism thereby possibly contributing to inferior bone quality. In order to explore this hypothesis, we further investigated and compared these metabolic parameters in osteoblasts and osteoclasts isolated from SP- and α-CGRP-deficient mice.

Methods: Primary osteoclasts were isolated from bone marrow and osteoblasts were isolated from long bones (femur, tibia and humerus) of female Tac1-/- (no SP), α-CGRP-/- and wildtype control (WT/C57Bl/6J) mice according to established protocols [1]. Proliferation was tested by BrdU labeling method; caspase 3/7-activity was measured to determine apoptosis; alkaline phosphatase (ALP) activity was assessed to determine osteoblast bone formation activity and cathepsin K activity was measured to determine osteoclast resorption activity.

Results and Conclusion: ALP activity was higher in osteoblasts from Tac1-/- mice after 7 days (early time point) and reduced after 21 days (late time point) of osteogenic culture when compared to WT mice. In osteoblasts obtained from α-CGRP-/- mice ALP activity was reduced after 14 days (middle time point). Apoptosis rate was higher in osteoblasts from α-CGRP-/- mice compared to osteoblasts from WT mice. Apoptosis rate was not affected in osteoblasts from Tac1-/- mice, but we measured a reduced apoptosis rate and a lower cathepsin K activity in osteoclasts from Tac1-/- mice when compared to WT control. Cathepsin K activity was also reduced in osteoclasts from α-CGRP-/- mice. We found no differences regarding proliferation of osteoblasts and osteoclasts from Tac1-/- and α-CGRP-/- mice when compared to controls.

Loss of SP and α-CGRP impacts on osteoblast bone matrix forming activity (ALP activity) at different culture time points and reduces bone resorption activity in osteoclasts (cathepsin K activity). Loss of SP reduces apoptosis rate in osteoclasts whereas loss of α-CGRP increases apoptosis rate in osteoblasts via upregulation of caspase 3/7 activity. Our results suggest that the sensory nervous system modulates osteoclast survival and osteoblast matrix forming activity via SP-dependent pathways, therefore SP has both, anabolic and catabolic activity. Via α-CGRP the sensory nervous system preferentially shows anabolic activity by increasing osteoblast survival and activity.