Histochemical assessment of the femora of Spontaneously Diabetic Torii-Lepr^fa (SDT-fa/fa) rats that mimic type II diabetes

Objective: To elucidate the mechanisms underlying diabetic osteoporosis, we conducted a comprehensive histological examination of the femora of Spontaneously Diabetic Torii-Lepr^fa (SDT-fa/fa) rats, an established model of obesity-related type 2 diabetes.

Materials and methods: Femora from 12 30-week-old male SDT-fa/fa rats and age-matched Sprague-Dawley (SD) rats (controls) were used for detailed histochemical analyses, including tartrate-resistant acid phosphatase (TRAP), cathepsin K, alkaline phosphatase (ALP), phosphoethanolamine/ phosphocholine phosphatase 1 (PHOSPHO1), dentin matrix protein (DMP)-1, matrix extracellular phosphoglycoprotein (MEPE), sclerostin, osteocalcin staining, silver impregnation, von Kossa staining, and micro-computed tomography (CT).

Results: Micro-CT and hematoxylin-eosin staining demonstrated significantly reduced trabecular bone volume in the femoral metaphyses of SDT-fa/fa rats. Although the number of TRAP-positive osteoclasts per bone surface remained comparable between both groups, SDT-fa/fa rats exhibited reduced areas of ALP-positive and PHOSPHO1-reactive mature osteoblasts/BS. Silver impregnation revealed a well-organized osteocytic lacunar-canalicular system in both groups. However, immunostaining identified aberrant DMP-1 and MEPE expression localized predominantly in the lacunae in SDT-fa/fa rats and in the lacunae and canaliculi of SD rats. Additionally, intense osteocalcin and sclerostin immunoreactivity was detected in osteocytes, along with a higher proportion of osteocalcin-positive osteocytes in SDT-fa/fa rats, distinguishing them from controls.

Conclusion: SDT-fa/fa rats displayed a significant decline in osteoblastic function and distinctive distribution patterns of osteocyte-derived peptides, suggesting that this diabetic model may manifest alterations in osteoblastic activity and the osteocytic lacunar-canalicular network.