Oxidative metabolism is impaired by phosphate deficiency during fracture healing and is mechanistically related to BMP induced chondrocyte differentiation.

Prior studies of acute phosphate restriction during the endochondral phase of fracture healing showed delayed chondrocyte differentiation was mechanistically linked to decreased bone morphogenetic protein signaling. In the present study, transcriptomic analysis of fracture callus gene expression in three strains of mice was used to identify differentially expressed (FDR = q ≤ 0.05) genes in response to phosphate (Pi) restriction. Ontology and pathway analysis of these genes showed that independent of genetic background, a Pi-deficient diet downregulated (p = 3.16 × 10-23) genes associated with mitochondrial oxidative phosphorylation pathways as well as multiple other pathways of intermediate metabolism. Temporal clustering was used to identify co-regulation of these specific pathways. This analysis showed that specific Ox/Phos, tricarboxylic acid cycle, pyruvate dehydrogenase. Arginine, proline metabolism genes, and prolyl 4-hydroxylase were all co-regulated in response to dietary Pi restriction. The murine C3H10T½ mesenchymal stem cell line was used to assess the functional relationships between BMP2-induced chondrogenic differentiation, oxidative metabolism and extracellular matrix formation. BMP2-induced chondrogenic differentiation of C3H10T½ was carried out in culture media in the absence or presence of ascorbic acid, the necessary co-factor for proly hydroxylation, and in media with normal and 25 % phosphate levels. BMP2 treatment led to decreased proliferation, increased protein accumulation and increased collagen and aggrecan gene expression. Across all conditions, BMP2 increased total oxidative activity and ATP synthesis. Under all conditions, the presence of ascorbate further increased total protein accumulation, proly-hydroxylation and aggrecan gene expression, oxidative capacity and ATP production. Lower phosphate levels only diminished aggrecan gene expression with no other effects of metabolic activity being observed. These data suggest that dietary phosphate restriction controls endochondral growth in vivo indirectly through BMP signaling, which upregulates oxidative activity that is linked to overall protein production and collagen hydroxylation.

Clinical Presentation and Outcomes of Patients With a Lumbar Far Lateral Herniated Nucleus Pulposus as Compared to Those With a Central or Paracentral Herniation.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: Examine pre- and postoperative outcomes between patients presenting with a central/paracentral versus a far lateral herniated nucleus pulposus (HNP) and assess whether significantly worse postoperative outcomes, assessed via patient self-reported survey, are associated with far lateral disc herniations. METHODS: We performed a retrospective cohort analysis of patients who underwent primary lumbar decompression between January 2008 and December 2015. Groups were divided based on herniation type, central/paracentral or far lateral. Patients with 3 months, or longer, of follow-up were included. Variables analyzed included demographics, American Society of Anesthesiologists (ASA) Score, Charleston Comorbidity Index (CCI), Oswestry Disability Index (ODI) scores, Visual Analog Scales (VAS) scores for the back and leg, 12-Item Short Form Mental and Physical Survey (SF-12) scores, and Veterans RAND 12-Item Mental and Physical Survey (VR-12) scores. RESULTS: A total of 100 patients met the inclusion criteria. Postoperative ODI scores for central/paracentral HNP were significantly lower compared to far lateral HNP. Patients with a far lateral disc herniation presented with significantly lower preoperative SF-12 and VR-12 scores. The improvement in ODI score from preoperative to final was significantly lower in the patients presenting with a far lateral HNP. CONCLUSIONS: Although patients with far lateral HNP present with worse preoperative outcome scores, they can expect similar symptom improvement to central or paracentral herniations following discectomy. This information can be used for future surgeons when weighing conservative versus surgical treatment of far lateral herniations.

Hypophosphatemia Regulates Molecular Mechanisms of Circadian Rhythm.

Transcriptomic analysis showed that the central circadian pathway genes had significantly altered expression in fracture calluses from mice fed a low phosphate diet. This led us to hypothesize that phosphate deficiency altered the circadian cycle in peripheral tissues. Analysis of the expression of the central clock genes over a 24-36 hour period in multiple peripheral tissues including fracture callus, proximal tibia growth plate and cardiac tissues after 12 days on a low phosphate diet showed higher levels of gene expression in the hypophosphatemia groups (p < 0.001) and a 3 to 6 hour elongation of the circadian cycle. A comparative analysis of the callus tissue transcriptome genes that were differentially regulated by hypophosphatemia with published data for the genes in bone that are diurnally regulated identified 1879 genes with overlapping differential regulation, which were shown by ontology assessment to be associated with oxidative metabolism and apoptosis. Network analysis of the central circadian pathway genes linked their expression to the up regulated expression of the histone methyltransferase gene EZH2, a gene that when mutated in both humans and mice controls overall skeletal growth. These data suggest that phosphate is an essential metabolite that controls circadian function in both skeletal and non skeletal peripheral tissues and associates its levels with the overall oxidative metabolism and skeletal growth of animals.