Panx3 deficiency in mice impairs bone fracture healing and causes transient hypoglycemia in neonatal animals

Panx3, belonging to the pannexin family of channel-forming transmembrane proteins, was previously identified predominantly expressed by bone-forming osteoblasts. Surprisingly however, only neonatal Panx3-deficient mice were found to display impaired ossification, whereas the skeleton was unaffected in adult animals. Furthermore, newborn Panx3-deficient mice displayed transient hypoglycemia, which was normalized at the age of 4 weeks, suggesting a potential role of Panx3 in linking glucose metabolism to bone growth. As bone regeneration largely recapitulates endochondral ossification during skeletal development, and as both processes require substantial amounts of energy, in the present study we investigated the role of Panx3 in fracture healing using a femoral osteotomy model. Female WT and Panx3-deficient mice, aged 12 weeks, were subject to a standardized femoral osteotomy. Healing outcomes were measured using µCT and non-decalcified histology, followed by gene expression analysis and genome-wide transcriptomics. In addition, serum samples were collected from patients with fracture or nonunion as well as healthy controls for the measurement of C1QTNF3. In WT mice, expression of Panx3 was upregulated in the fractured callus during the course of fracture healing. Panx3-deficient mice displayed a striking impairment of bone regeneration, associated with a dysregulated inflammatory response and decreased type-H vessel formation. Transcriptomic analysis of the facture callus further identified differential expression of genes involved in glucose homeostasis, including C1qtnf3, which encodes a glucose-lowering adipokine. Although serum glucose levels in Panx3-deficient animals were moderately reduced during fracture healing, the most pronounced hypoglycemia was found in neonatal Panx3-deficient mice, which also displayed a three-fold increase in serum C1qtnf3 concentrations. Last, we observed increased serum level of C1QTNF3 in patients with fractures compared to healthy controls, and decreased concentrations in patients with nonunion. Taken together, our data demonstrate that Panx3, at least in mice, is not only essential for skeletal fracture healing, but also involved in the previously established regulation of energy metabolism by osteoblasts.