neuropeptide-y and Tibial-Fractures

Pain is a critical component hindering recovery and regaining of function after surgery, particularly in the elderly. Understanding the role of pain signaling after surgery may lead to novel interventions for common complications such as delirium and postoperative cognitive dysfunction. Using a model of tibial fracture with intramedullary pinning in male mice, associated with cognitive deficits, we characterized the effects on the primary somatosensory system. Here we show that tibial fracture with pinning triggers cold allodynia and up-regulates nerve injury and inflammatory markers in dorsal root ganglia (DRGs) and spinal cord up to 2 wk after intervention. At 72 h after surgery, there is an increase in activating transcription factor 3 (ATF3), the neuropeptides galanin and neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), as well as neuroinflammatory markers including ionized calcium-binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and the fractalkine receptor CX3CR1 in DRGs. Using an established model of complete transection of the sciatic nerve for comparison, we observed similar but more pronounced changes in these markers. However, protein levels of BDNF remained elevated for a longer period after fracture. In the hippocampus, BDNF protein levels were increased, yet there were no changes in Bdnf mRNA in the parent granule cell bodies. Further, c-Fos was down-regulated in the hippocampus, together with a reduction in neurogenesis in the subgranular zone. Taken together, our results suggest that attenuated BDNF release and signaling in the dentate gyrus may account for cognitive and mental deficits sometimes observed after surgery.

Topics: Activating Transcription Factor 3; Animals; Brain-Derived Neurotrophic Factor; Calcium-Binding Proteins; Cognitive Dysfunction; CX3C Chemokine Receptor 1; Dentate Gyrus; Fracture Fixation, Intramedullary; Galanin; Ganglia, Spinal; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Hyperalgesia; Male; Mice; Mice, Inbred C57BL; Microfilament Proteins; Neuropeptide Y; Pain; Proto-Oncogene Proteins c-fos; Sciatic Nerve; Signal Transduction; Spinal Cord; Tibial Fractures

Neuropeptide Y acting via it's Y1 receptor represents a powerful pathway in the control of bone mass. The global or osteoblast-specific Y1 receptor deletion induces pronounced bone anabolic effects in mice. However, the contribution of Y1 receptor deletion in bone repair/healing remained to be clarified. Therefore, in this study we characterized the role of Y1 receptor deletion in fracture healing. Closed tibial fractures were generated in germline (Y1 (-/-) ) and osteoblastic-specific Y1 receptor knockout mice. The progression of tibial repair monitored from 1- until 6-weeks post-fracture demonstrated that in Y1 (-/-) mice there is a delay in fracture repair, as seen by a decrease in bone callus volume and callus strength. Moreover, the histological features included elevated avascular and cartilage area and consequently delayed cartilage removal, and hence impaired union. Interestingly, this delay in bone repair was not related directly to Y1 receptors expressed by mature osteoblasts. These findings suggest that the global absence of the Y1 receptor delays fracture healing, through impairing the early phases of fracture repair to achieve bony union. The data acquired on the role of Y1 receptor signaling disruption in bone regeneration is critical for the design of future therapeutic strategies.

Topics: Animals; Disease Models, Animal; Female; Fracture Healing; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neuropeptide Y; Osteoblasts; Receptors, Neuropeptide Y; Signal Transduction; Tibia; Tibial Fractures; X-Ray Microtomography

Autonomic neuropeptide Y (NPY) is involved in local bone remodeling via the central nervous system. However, the role of peripheral neuronal NPY in fracture healing is not known. We investigated the relationship between bone healing and side-specific occurrence of NPY in angular and straight fractures.. Tibial fractures in Sprague-Dawley rats were fixed with intramedullary pins in straight alignment and anterior angulation. The samples were analyzed by radiography, histology, and immunohistochemistry (IHC) between 3 and 56 days postfracture.. In the angular fractures, radiography and histology showed a 3.5-fold increase in callus thickness on the concave side compared to the convex side at day 21, whereas a 0.2-fold reduction in callus thickness was seen on the convex side between days 21 and 56. IHC showed regenerating NPY fibers in the callus and woven bone in both fractures at day 7. In angular fractures, a 5-fold increase in NPY fibers was observed on the concave side compared to the convex side at 7 days, whereas a 6-fold increase in NPY fibers was seen on the convex side between 21 and 56 days; only a 0.1-fold increase in NPY fibers was seen on the concave side during the same time period. In straight fractures, similar bony and neuronal changes were observed on both sides.. The increase in NPY innervation on the convex side appears to correlate with the loss of callus thickness on the same side in angular fractures. Our results highlight the probable function of the peripheral NPY system in local bone remodeling.

Topics: Animals; Bone Remodeling; Fracture Healing; Immunohistochemistry; Male; Nerve Fibers; Neuropeptide Y; Radiography; Rats; Rats, Sprague-Dawley; Tibia; Tibial Fractures

Neural influences have been associated with fracture healing through clinical observations and experimental procedures. This work was intended to study the reliability of sciatic nerve section as a model of denervation of tibial fracture. Rats were subjected to a standardized fracture with or without simultaneous nerve resection. The fractures were fixed by intramedullary nails, and the legs were immobilized to prevent differential loading. On Day 25 posttrauma, nerve fibers were found in the periosteum, fracture callus, and bone-marrow space. Most fibers expressed growth-associated protein 43 (GAP-43/B-50), suggesting actively ongoing neural regeneration. Additional characterization of the type of innervation revealed an extensive distribution of sensory fibers containing calcitonin gene-related peptide, a neuropeptide with potent vasodilatory actions. Sciatic nerve section reduced all free and some perivascular calcitonin gene-related peptide-containing fibers, although regenerating nerve fibers still were evident in the bone marrow. Radiographs showed an increased callus formation in rats with sciatic nerve section, suggesting involvement of neural factors in the healing process. The results show that sciatic nerve section is not a reliable model for a total denervation of tibial fracture. Hard tissue injury induces proliferation of nerves, probably by production of chemotactic factors to attract neural targeting and regeneration of injured nerves.

Topics: Animals; Bony Callus; Calcitonin Gene-Related Peptide; Fracture Healing; GAP-43 Protein; Growth Substances; Male; Membrane Glycoproteins; Nerve Fibers; Nerve Regeneration; Nerve Tissue Proteins; Neuropeptide Y; Periosteum; Rats; Rats, Wistar; Sciatic Nerve; Thiolester Hydrolases; Tibial Fractures; Ubiquitin Thiolesterase