Mieczkowska, A. | bioRxiv Science

bioRxiv2024

The GLP-1 analogue, exendin-4, improves bone material properties and strength through a central relay in ovariectomized mice

Glucagon-like peptide-1 (GLP-1) has previously been shown to be indispensable for optimal bone strength by acting at the bone material level. However, it was not fully clear whether the effects of GLP-1 were mediated by direct or indirect actions on bone cells. In the present study, we were unable to demonstrate the expression of the GLP-1 receptor (GLP-1r) in bone tissue at the gene expression level using qPCR and in situ hybridization, or at the protein level. Furthermore, the peripheral administration of exendin-4, a specific GLP-1r agonist, in ovariectomized (OVX) BALB/c mice enhanced post-yield displacement (18%) and energy-to-fracture (24%), as well as bone volume/total volume (BV/TV) (11%), trabecular number (Tb.N) (6%), and collagen maturity (18%). These bone effects were still observed when exendin-4 was centrally administered into the lateral cerebral ventricle. On the other hand, the peripheral administration of exendin-4 coupled to bovine serum albumin, a GLP-1r agonist that cannot penetrate the brain, failed to replicate the positive effects on bone despite increased calcitonin secretion. Altogether, these data confirm that GLP-1r agonists represent an interesting approach for managing bone fragility due to ovariectomy, but also suggest that GLP-1r agonists require a central relay yet to be identified to exert positive effects on bone physiology. Further studies are needed to decipher the mechanisms of action of GLP-1 and GLP-1r agonists on bone physiology.

physiology↗

bioRxiv2023

Validation of Fourier transform infrared microspectroscopy for the evaluation of enzymatic cross-linking of bone collagen

Enzymatic cross-linking of the bone collagen is important to resist to crack growth and to increased flexural strength. In the present study, we proposed a new method for assessment of enzymatic cross-link based on FTIR microspectroscopy that takes into account secondary structure of type I collagen. Briefly, femurs were collected from sham or ovariectomized mice and subjected either to LC-MS or embedded in polymethylmethacrylate, cut and analyzed by FTIR microspectroscopy. FTIR acquisition were recorded before and after UV exposure or acid treatment. In addition, femurs from a second animal study were used to compare gene expression of Plod2 and Lox enzymes and enzymatic cross-links determined by FTIR microspectroscopy. We evidenced here that intensities and areas of subbands located at [~]1660 cm-1, [~]1680 cm-1 and [~]1690 cm-1 were positively and significantly associated with the concentration of pyridinoline (PYD), deoxypyridinoline (DPD) or immature dihydroxylysinonorleucine (DHLNL) / hydroxylysinonorleucine (HLNL) cross-links. Seventy-two hours exposure to UV light significantly reduced by [~]86% and [~]89% the intensity and area of the [~]1660 cm-1 subband. Similarly, 24 hours of acid treatment significantly reduced by 78% and 76% the intensity and area of the [~]1690 cm-1 subband. Plod2 and Lox expression were also positively associated to the signal of the [~]1660 cm-1 and [~]1690 cm-1 subbands. In conclusion, our study provided a new method for decomposing the amide I envelope of bone section that positively correlates with PYD and immature collagen cross-links. This method allows for investigation of tissue distribution of enzymatic cross-links in bone section.

biochemistry↗