WNT Pathway and Bone Fragility in Postmenopausal Women with Type 2 Diabetes

Fragility fractures are major complications in type 2 diabetes (T2D), but mechanisms underlying bone fragility are still poorly clarified. Bone mineral density (BMD) underestimates T2D fracture incidence, since a normal or even higher BMD is associated with a greater fracture risk than healthy population. We hypothesized that bone fragility in T2D results from poor bone microarchitecture and bone quality caused by WNT signaling impairment and lower bone formation. We aimed to evaluate the association between bone gene expression of WNT pathway and features of bone microarchitecture and strength. We enrolled T2D (n=13) and nondiabetic (controls, n=75) postmenopausal women undergoing standard hip arthroplasty. Serum and proximal femur samples from recruited subjects were collected at the moment of surgical procedure. Gene expression of sclerostin (SOST), WNT5a, WNT10b, SFRP5, GSK3β, osteocalcin and RUNX2 was analyzed by real-time PCR. Total-body, lumbar and femoral BMD were assessed by bone densitometry. A trabecular core from bone samples was analyzed by Micro X-ray computed tomography and by compression tests. Age (75.23 ± 8.47 vs. 73.24 ± 5.77) and BMI (29.92 ± 5.38 vs. 27.68 ± 5.62 Kg/m2) did not differ between T2D and controls respectively. Glycated hemoglobin was 6.48 ± 1.7 mmol/mol. We found that T2D subjects had no differences in BMD and in bone microarchitecture parameters compared to controls. Neither bone turnover nor WNT serum markers differed among groups. SOST gene expression was increased (p=0.003) whereas RUNX2 expression was decreased in T2D vs. controls (p=0.017), independently by BMI and age. Osteocalcin and other WNT related genes expression did not differ among groups. Compression tests did not show impairment in bone strength in T2D vs. controls. In conclusion, although a good glycemic control and no alterations in bone density, microarchitecture and strength, we found an increase in SOST and a decrease in RUNX2 gene expression, implying a lower bone formation in T2D. Disclosure A. Piccoli: None. F. Cannata: None. F. Russo: None. V.L. Greto: None. C. Isgrò: None. G. Leanza: None. R. Strollo: None. C. Massaroni: None. C. Pedone: None. S. Silvestri: None. G. Vadalà: None. V. Denaro: None. T. Bisogno: None. R. Papalia: None. P. Pozzilli: None. M. Maccarrone: None. N. Napoli: None. Funding Campus Bio-Medico University