IADR Abstract Archives
FOXO1 Deletion Reverses the Effect of Diabetic-Induced Impaired Fracture Healing
Objectives: Diabetes impairs fracture healing. We previously suggested that a dominant mechanism was premature loss of cartilage during endochondral bone formation. Based on these results we tested the hypothesis that chondrocytes regulate osteoclast formation in diabetes-impaired fracture healing and that it is controlled by the transcription factor FOXO1.
Methods: Closed fracture of the femur was induced in mice with lineage specific FOXO1 deletion in chondrocytes Col2a1Cre+/FOXO1L/L . The control mice had FOXO1 gene present (Col2a1Cre-/FOXO1L)/). Mice were rendered diabetic by multiple streptozotocin injections. The normoglycemic group received vehicle alone. Specimens were collected at 10 days (cartilage formed), 16 days (transition from cartilage to bone formation) and 22 days (primary bone formed). The cartilage area was measured using Safranin-O/fast green staining. Osteoclasts were counted as cathepsin K positive cells. The expression of cathepsin K and RANKL were determined by quantitative immunostaining with specific antibodies compared to control IgG. MicroCT was used to measure the callus volume and the mineralized bone. Statistical analysis used a 2-way ANOVA test. Results with p<0.05 were considered significant.
Results: All the groups showed similar cartilage areas at day 10. At day16 the diabetic group had 84% less cartilage area than the normal (P <0.05). The accelerated cartilage loss in the diabetic group was completely reversed when FOXO1 was deleted (P<0.05). Diabetic mice had 3 times more cathepsin K positive cells in comparison to normals. This change could be accounted for by changes in RANKL expression which was 2-fold greater in the diabetic mice compared to the normal mice (P <0.05). However, when FOXO1 was deleted in the diabetic animals, both cathepsin K and RANKL were reduced to normal levels (P <0.05). Bone volume in the diabetic group was 30% and 40% less than the normoglycemic animals on day 16 and 22 respectively (P <0.05). However, the effect of diabetes was rescued to normal levels upon FOXO1 deletion (P <0.05).
Conclusions: Our data indicates that FOXO1 drives RANKL expression in chondrocytes and resorption of cartilage. FOXO1 deletion reverses diabetes-enhanced osteoclast formation and prevents the premature loss of cartilage which results in a better bone healing.
Methods: Closed fracture of the femur was induced in mice with lineage specific FOXO1 deletion in chondrocytes Col2a1Cre+/FOXO1L/L . The control mice had FOXO1 gene present (Col2a1Cre-/FOXO1L)/). Mice were rendered diabetic by multiple streptozotocin injections. The normoglycemic group received vehicle alone. Specimens were collected at 10 days (cartilage formed), 16 days (transition from cartilage to bone formation) and 22 days (primary bone formed). The cartilage area was measured using Safranin-O/fast green staining. Osteoclasts were counted as cathepsin K positive cells. The expression of cathepsin K and RANKL were determined by quantitative immunostaining with specific antibodies compared to control IgG. MicroCT was used to measure the callus volume and the mineralized bone. Statistical analysis used a 2-way ANOVA test. Results with p<0.05 were considered significant.
Results: All the groups showed similar cartilage areas at day 10. At day16 the diabetic group had 84% less cartilage area than the normal (P <0.05). The accelerated cartilage loss in the diabetic group was completely reversed when FOXO1 was deleted (P<0.05). Diabetic mice had 3 times more cathepsin K positive cells in comparison to normals. This change could be accounted for by changes in RANKL expression which was 2-fold greater in the diabetic mice compared to the normal mice (P <0.05). However, when FOXO1 was deleted in the diabetic animals, both cathepsin K and RANKL were reduced to normal levels (P <0.05). Bone volume in the diabetic group was 30% and 40% less than the normoglycemic animals on day 16 and 22 respectively (P <0.05). However, the effect of diabetes was rescued to normal levels upon FOXO1 deletion (P <0.05).
Conclusions: Our data indicates that FOXO1 drives RANKL expression in chondrocytes and resorption of cartilage. FOXO1 deletion reverses diabetes-enhanced osteoclast formation and prevents the premature loss of cartilage which results in a better bone healing.
