Osteoblast RNA Sequencing in T1D Mice Reveals Genetic Signature of Maladaptation to Hypoxia and Compromised Collagen Synthesis

초록

The main feature of skeletal abnormality in type 1 diabetes (T1D) is low bone turnover with decreased osteoblastic bone formation [1, 2]. However, the mechanism of osteoblast dysfunction remains unclear. We generated T1D mice using low dose streptozotocin (STZ). T1D mice showed lower bone mass (g/cm2) at the femur (0.07 vs. 0.09*) and trends at lumbar spine (0.05 vs. 0.06, p=0.08) compared with control group at 8 weeks after inducing T1D. Osteoblasts were differentiated using bone marrow mesenchymal stem cells, and RNAseq was performed to analyze the transcriptome of osteoblasts. In gene set enrichment analysis, several pathways including immune, hypoxia, and glycolytic pathway were enriched. The osteogenic genes panel showed decreased Bglap and Col1a1 expression, together with lower expression of Bmp2 and Wnt5a, suggesting decreased bone formation might be related to the suppression of BMP and WNT signaling. Particularly, P4ha2, encoding prolyl 4-hydroxylase subunit alpha-2, which are responsible for posttranslational modification of collagen were downregulated in T1D osteoblasts (log2FC = - 1.7**). Among genes in hypoxia pathway, Egln3 encoding prolyl hydroxylase domain-containing protein 2 and Vhl encoding von Hippel-Lindau tumor suppressor, both of which stabilize HIF-? were downregulated (log2FC = - 2.8** and - 0.31*, respectively) likely for promoting HIF-? dependent gene expression in hypoxia. However, genes of the growth signaling pathway, namely Pgf, Vegfa, and Igf1r, which were normally upregulated in hypoxic condition, were downregulated (log2FC = - 3.1**, - 0.4* and - 0.5**, respectively). Altogether, our findings suggest that maladaptation to hypoxic condition in T1D with compromised growth signaling pathway and impaired collagen synthesis might be related to osteoblasts dysfunction in T1D bone. (* p < 0.05 and ** p < 0.001)