Identification of novel genes associated with fracture healing in osteoporosis induced by Krm2 overexpression or Lrp5 deficiency

Abstract

The aim of the present study was to screen potential key genes associated with osteoporotic fracture healing. The microarray data from the Gene Expression Omnibus database accession number GSE51686, were downloaded and used to identify differentially expressed genes (DEGs) in fracture callus tissue samples obtained from the femora of type I collagen (Col1a1)‑kringle containing transmembrane protein 2 (Krm2) mice and low density lipoprotein receptor‑related protein 5‑/‑ (Lrp5‑/‑) transgenic mice of osteoporosis compared with those in wild‑type (WT) mice. Enrichment analysis was performed to reveal the DEG function. In addition, protein‑protein interactions (PPIs) of DEGs were analyzed using the Search Tool for the Retrieval of Interacting Genes database. The coexpression associations between hub genes in the PPI network were investigated, and a coexpression network was constructed. A total of 841 DEGs (335 upregulated and 506 downregulated) were identified in the Col1a1‑Krm2 vs. the WT group, and 50 DEGs (16 upregulated and 34 downregulated) were identified in the Lrp5‑/‑ vs. the WT group. The DEGs in Col1a1‑Krm2 mice were primarily associated with immunity and cell adhesion (GO: 0007155) functions. By contrast, the DEGs in Lrp5‑/‑ mice were significantly associated with muscle system process (GO: 0003012) and regulation of transcription (GO: 0006355). In addition, a series of DEGs demonstrated a higher score in the PPI network, and were observed to be coexpressed in the coexpression network, and included thrombospondin 2 (Thbs2), syndecan 2 (Sdc2), FK506 binding protein 10 (Fkbp10), 2'‑5'-oligoadneylate synthase‑like protein 2 (Oasl2), interferon induced protein with tetratricopeptide repeats (Ifit) 1 and Ifit2. Thbs2 and Sdc2 were significantly correlated with extracellular matrix‑receptor interactions. The results suggest that Thbs2, Sdc2, Fkbp10, Oasl2, Ifit1 and Ifit2 may serve important roles during the fracture healing process in osteoporosis. In addition, this is the first study to demonstrate that Sdc2, Fkbp10, Oasl2, Ifit1 and Ifit2 may be associated with osteoporotic fracture healing.

Figure 1.

Venn diagrams of differentially expressed genes between Col1a1-Krm2 vs. WT and Lrp5^−/− vs. WT groups. (A) Venn diagram of upregulated genes. (B) Venn diagram of downregulated genes. Col1a1, type I collagen; Krm2, kringle containing transmembrane protein 2; Lrp5, low density lipoprotein receptor-related protein 5; Col1a1-Krm2, Col1a1-Krm2 transgenic mice; Lrp5^−/−, mice deficient in Lrp5; WT, wild-type mice.

Figure 2.

GO and KEGG pathway terms enriched by differentially expressed genes between (A) Col1a1-Krm2 transgenic mice and wild-type mice and (B) Lrp5^−/− mice and wild-type mice. ‘Up’ represents upregulated genes and ‘Down’ represents downregulated genes. Red bars indicate the P-values, and blue bars indicate the gene count. GO, Gene Ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes; Col1a1, type I collagen; Krm2, kringle containing transmembrane protein 2; Lrp5, low density lipoprotein receptor-related protein 5; BP, biological process; CC, cellular component; MF, molecular function.

Figure 3.

Protein-protein interaction network of differentially expressed genes as determined using the Search Tool for the Retrieval of Interacting Genes database (http://string-db.org/). Each node represents a protein, and each line represents the interaction between the two proteins.

Figure 4.

Heat map of hub genes in the protein-protein interaction network in WT, Lrp5^−/− and Col1a1-Krm2 mice. Each row represents a single gene and each column represents a sample. The gradual color alteration from orange to blue represents the process from upregulation to downregulation of genes. WT, wild-type; Col1a1, type I collagen; Krm2, kringle containing transmembrane protein 2; Lrp5, low density lipoprotein receptor-related protein 5.

Figure 5.

Coexpression network of hub genes and additional differentially expressed genes. Red-colored nodes represent hub genes in the protein-protein interaction network, and blue-colored genes represent differentially expressed genes that are not hub genes. Each node represents a protein, and each line represents the coexpression association between the two genes. Solid lines indicate the coexpression (pearson correlation coefficient) >0.9 (positive correlation), and the dotted lines indicate the coexpression (pearson correlation coefficient) <0.9 (negative correlation).