The Effect of Diabetes on Perilacunar Composition, Mechanics, and the Osteocyte Lacuno-canalicular Network
Creators: name: Bolger, Morgan
Publisher: name: My University
Year: 2022
Subjects: subject: The Effect of Diabetes on Perilacunar Composition, Mechanics, and the Osteocyte Lacuno-canalicular Network
subject: Examination of the Key Morphological and Compositional Traits Contributing to Low Strength in Human Cadaveric Femora
subject: Biomedical Engineering
subject: FOS: Medical engineering
subject: Engineering

description: The number of adults in the U.S. with type 1 (T1D) and type 2 diabetes (T2D) rose to 30.2 million in 2015 and is projected to reach 44.1 million by 2034. In T1D and T2D there is a 6.94- and 1.38 – times greater risk of hip fracture, respectively. The slight decrease in bone mineral density (BMD) with T1D is not enough to explain the magnitude of increased fracture risk, suggesting that perturbed bone material contributes to decreased strength. Osteocytes are the most abundant cell type in bone and remodel their local perilacunar matrix in response to a variety of stimuli and diseases. How the perilacunar composition, local mechanics, and osteocyte lacuno-canalicular network (OLCN) are affected by T1D, and the contribution of these local structural, compositional, and mechanical changes to the decline in whole-bone functional properties that occurs with diabetes remains unclear. The central hypotheses are 1) decreased whole-bone mechanical properties in diabetes are dictated by local perilacunar composition and mechanics, and 2) the OLCN is less dense and has fewer canaliculi with diabetes and these OLCN measures correlate with perilacunar composition and mechanics. To test these hypotheses, a diabetic mouse model (induction via low-dose streptozotocin) was used. Mice were sacrificed at baseline (BL) and at 3 (D3) and 7 weeks (D7) following confirmation of diabetes, with age-matched controls (C3, C7). Femora were then subjected to a thorough morphological (μCT), mechanical (four-point bending, nanoindentation), and compositional (HPLC for collagen cross-links, Raman spectroscopy) analysis at the whole bone and local (perilacunar and intracortical) levels. Bone turnover was assessed by dynamic histomorphometry and serum markers. Mineralized bone sections were infiltrated with rhodamine, imaged and advanced computational tools were used to quantify morphology and topology of the OLCN. At the whole-bone level, D7 mice exhibited 10.7% lower ultimate load and 26.4% lower post-yield work relative to C7, with minimal changes to bone geometry. These mechanical changes coincided with 52.2% higher levels of pentosidine at D7 compared to C7, but no difference in enzymatic cross-linking. At the local level, the creep distance increased while modulus and hardness decreased in the perilacunar region relative to the intracortical for D7 mice, suggesting a spatial uncoupling in skeletal adaptation. D7 mice also exhibited increased collagen maturity in the Raman 1660/1690 cm-1 ratio at both regions relative to C7. The perilacunar collagen maturity was predictive of post-yield work (46% of the variance), but perilacunar measures were not predictive of ultimate load which was better explained by cortical area (26% of variance). Both diabetic groups exhibited a reduction in peripheral canaliculi, and nodes relative to BL, with no change in lacunae morphology and, in D7 only, decreased canaliculi tortuosity. These peripheral network changes preceded decreases in bone formation rate (BFR) at D7. The number of nodes exhibited mild predictive power over BFR (15% of variance). However, the number of nodes better explained BV/TV (45%), and ultimate load (31%), and the number of canaliculi branches explained local elastic work (30%). These results show, for the first time, that the OLCN and perilacunar composition interact and affect whole-bone level mechanical properties. This work implicates perilacunar tissue and a diminished OLCN in diabetic skeletal fragility and reduced bone turnover, respectively, and as targets for future therapies.