Skeletal Response to Insulin in the Naturally Occurring Type 1 Diabetes Mellitus Mouse Model

Activation of BK channels prevents diabetes-induced osteopenia by regulating mitochondrial Ca2+ and SLC25A5/ANT2-PINK1-PRKN-mediated mitophagy

Osteopenia and osteoporosis are among the most common metabolic bone diseases and represent major public health problems, with sufferers having an increased fracture risk. Diabetes is one of the most common diseases contributing to osteopenia and osteoporosis. However, the mechanisms underlying diabetes-induced osteopenia and osteoporosis remain unclear. Bone reconstruction, including bone formation and absorption, is a dynamic process. Large-conductance Ca2+-activated K+ channels (BK channels) regulate the function of bone marrow-derived mesenchymal stem cells, osteoblasts, and osteoclasts. Our previous studies revealed the relationship between BK channels and the function of osteoblasts via various pathways under physiological conditions. In this study, we reported a decrease in the expression of BK channels in mice with diabetes-induced osteopenia. BK deficiency enhanced mitochondrial Ca2+ and activated classical PINK1 (PTEN induced putative kinase 1)-PRKN/Parkin (parkin RBR E3 ubiquitin protein ligase)-dependent mitophagy, whereas the upregulation of BK channels inhibited mitophagy in osteoblasts. Moreover, SLC25A5/ANT2 (solute carrier family 25 (mitochondrial carrier, adenine nucleotide translocator), member 5), a critical inner mitochondrial membrane protein participating in PINK1-PRKN-dependent mitophagy, was also regulated by BK channels. Overall, these data identified a novel role of BK channels in regulating mitophagy in osteoblasts, which might be a potential target for diabetes-induced bone diseases.

Icariin accelerates bone regeneration by inducing osteogenesis-angiogenesis coupling in rats with type 1 diabetes mellitus

BACKGROUND

Icariin (ICA), a natural flavonoid compound monomer, has multiple pharmacological activities. However, its effect on bone defect in the context of type 1 diabetes mellitus (T1DM) has not yet been examined.

AIM

To explore the role and potential mechanism of ICA on bone defect in the context of T1DM.

METHODS

The effects of ICA on osteogenesis and angiogenesis were evaluated by alkaline phosphatase staining, alizarin red S staining, quantitative real-time polymerase chain reaction, Western blot, and immunofluorescence. Angiogenesis-related assays were conducted to investigate the relationship between osteogenesis and angiogenesis. A bone defect model was established in T1DM rats. The model rats were then treated with ICA or placebo and micron-scale computed tomography, histomorphometry, histology, and sequential fluorescent labeling were used to evaluate the effect of ICA on bone formation in the defect area.

RESULTS

ICA promoted bone marrow mesenchymal stem cell (BMSC) proliferation and osteogenic differentiation. The ICA treated-BMSCs showed higher expression levels of osteogenesis-related markers (alkaline phosphatase and osteocalcin) and angiogenesis-related markers (vascular endothelial growth factor A and platelet endothelial cell adhesion molecule 1) compared to the untreated group. ICA was also found to induce osteogenesis-angiogenesis coupling of BMSCs. In the bone defect model T1DM rats, ICA facilitated bone formation and CD31hiEMCNhi type H-positive capillary formation. Lastly, ICA effectively accelerated the rate of bone formation in the defect area.

CONCLUSION

ICA was able to accelerate bone regeneration in a T1DM rat model by inducing osteogenesis-angiogenesis coupling of BMSCs.

The combined treatment of insulin and naringin improves bone properties in rats with type 1 diabetes mellitus

We have studied the effects of individual and combined treatment of insulin (I) and naringin (NAR) on the bone structure and biomechanical properties of femurs from streptozotocin (STZ)-induced diabetic rats. Male Wistar rats were divided into five groups: (1) controls, (2) STZ-induced diabetic rats, (3) STZ-induced diabetic rats treated with I, (4) STZ-induced diabetic rats treated with NAR, and (5) STZ-induced diabetic rats treated with I + NAR. Bone mineral density (BMD), bone histomorphometry, biomechanical testing, and bone biomarker expressions were accomplished in femur of all animals, as well as serum biochemical analyses. The combined treatment of I + NAR increased the body weight and the femur BMD from STZ-induced diabetic rats. The bone biomechanical properties and the bone morphology of the femurs from STZ-induced diabetic rats were also improved by the combined treatment. The increased number of osteoclasts in STZ-induced diabetic rats was partially prevented by I, NAR, or I + NAR. NAR or I + NAR completely blocked the decrease in the number of osteocalcin (+) cells in the femur from STZ-induced diabetic rats. RUNX family transcription factor 2 immunostaining was much lower in STZ-induced diabetic rats than in control animals; the combination of I + NAR totally blocked this effect. The combined treatment not only ameliorated bone quality and function, but also normalized the variables related to glucose metabolism. Therefore, the combination of I + NAR might be a better therapeutic strategy than the individual I or NAR administration to reduce bone complications in diabetic patients.

Genetic activation of glycolysis in osteoblasts preserves bone mass in type I diabetes

Type I diabetes (T1D) impairs bone accrual in patients, but the mechanism is unclear. Here in a murine monogenic model for T1D, we demonstrate that diabetes suppresses bone formation resulting in a rapid loss of both cortical and trabecular bone. Single-cell RNA sequencing uncovers metabolic dysregulation in bone marrow osteogenic cells of diabetic mice. In vivo stable isotope tracing reveals impaired glycolysis in diabetic bone that is highly responsive to insulin stimulation. Remarkably, deletion of the insulin receptor reduces cortical but not trabecular bone. Increasing glucose uptake by overexpressing Glut1 in osteoblasts exacerbates bone defects in T1D mice. Conversely, activation of glycolysis by Pfkfb3 overexpression preserves both trabecular and cortical bone mass in the face of diabetes. The study identifies defective glucose metabolism in osteoblasts as a pathogenic mechanism for osteopenia in T1D, and furthermore implicates boosting osteoblast glycolysis as a potential bone anabolic therapy.

Remodeling of the periodontal ligament and alveolar bone during axial tooth movement in mice with type 1 diabetes

OBJECTIVES

To observe the elongation of the axial tooth movement in the unopposed rodent molar model with type 1 diabetes mellitus and explore the pathological changes of periodontal ligament and alveolar bone, and their correlation with tooth axial movement.

METHODS

The 80 C57BL/6J mice were randomly divided into the streptozotocin(STZ)-injected group (n = 50) and the control group (n = 30). Mice in the streptozotocin(STZ)-injected group were injected intraperitoneal with streptozotocin (STZ), and mice in the control group were given intraperitoneal injection of equal doses of sodium citrate buffer. Thirty mice were randomly selected from the successful models as the T1DM group. The right maxillary molar teeth of mice were extracted under anesthesia, and allowed mandibular molars to super-erupt. Mice were sacrificed at 0, 3, 6,9, and 12 days. Tooth elongation and bone mineral density (BMD) were evaluated by micro-CT analysis(0,and 12 days mice). Conventional HE staining, Masson staining and TRAP staining were used to observe the changes in periodontal tissue(0, 3, 6, 9, and 12 days mice). The expression differences of SPARC, FGF9, BMP4, NOGGIN, and type I collagen were analyzed by RT-qPCR.

RESULTS

After 12 days of tooth extraction, our data showed significant super-eruption of mandibular mouse molars of the two groups. The amount of molar super-eruption in the T1DM group was 0.055mm( ± 0.014mm), and in the control group was 0.157( ± 0.017mm). The elongation of the T1DM mice was less than that of the control mice(P<0.001). It was observed that the osteoclasts and BMD increased gradually in both groups over time. Compared with the control group, the collagen arrangement was more disordered, the number of osteoclasts was higher (P<0.05), and the increase of bone mineral density was lower(2.180 ± 0.007g/cm³ vs. 2.204 ± 0.006g/cm³, P<0.001) in the T1DM group. The relative expression of SPARC, FGF9, BMP4, and type I collagen in the two groups increased with the extension of tooth extraction time while NOGGIN decreased. The relative expression of all of SPARC, FGF9, BMP4, and type I collagen in the T1DM group were significantly lower, and the expression of NOGGIN was higher than that in the control group (P<0.05).

CONCLUSION

The axial tooth movement was inhibited in type 1 diabetic mice. The result may be associated with the changes of periodontal ligament osteoclastogenic effects and alveolar bone remodeling regulated by the extracellular matrix and osteogenesis-related factors.

Effects of diabetes on osteocytes

PURPOSE OF REVIEW

Better understanding of the mechanisms underlying skeletal dysfunction in the context of diabetes is needed to guide the development of therapeutic interventions to reduce the burden of diabetic fractures. Osteocytes, the 'master regulators' of bone remodeling, have emerged as key culprits in the pathogenesis of diabetes-related skeletal fragility.

RECENT FINDINGS

Both type 1 diabetes and type 2 diabetes cause chronic hyperglycemia that, over time, reduces bone quality and bone formation. In addition to acting as mechanosensors, osteocytes are important regulators of osteoblast and osteoclast activities; however, diabetes leads to osteocyte dysfunction. Indeed, diabetes causes the accumulation of advanced glycation end-products and senescent cells that can affect osteocyte viability and functions via increased receptor for advanced glycation endproducts (RAGE) signaling or the production of a pro-inflammatory senescence-associated secretory phenotype. These changes may increase osteocyte-derived sclerostin production and decrease the ability of osteocytes to sense mechanical stimuli thereby contributing to poor bone quality in humans with diabetes.

SUMMARY

Osteocyte dysfunction exists at the nexus of diabetic skeletal disease. Therefore, interventions targeting the RAGE signaling pathway, senescent cells, and those that inhibit sclerostin or mechanically stimulate osteocytes may alleviate the deleterious effects of diabetes on osteocytes and bone quality.

Mouse models of type 1 diabetes and their use in skeletal research

PURPOSE OF REVIEW

In this review, we describe the three primary mouse models of insulin-deficiency diabetes that have been used to study the effects of type 1 diabetes (T1D) on skeletal outcomes. These models include streptozotocin (chemically)-induced diabetes, autoimmune-mediated diabetes (the nonobese diabetes mouse), and a mutation in the insulin gene (the Akita mouse). We then describe the skeletal findings and/or skeletal phenotypes that have been delineated using these models.

RECENT FINDINGS

Humans with T1D have decreased bone mineral density and an increased risk for fragility fracture. Mouse models of insulin-deficiency diabetes (hereafter denoted as T1D) in many ways recapitulate these skeletal deficits. Utilizing techniques of microcomputed tomography, bone histomorphometry, biomechanical testing and fracture modeling, bone biomarker analysis, and Raman spectroscopy, mouse models of T1D have demonstrated abnormalities in bone mineralization, bone microarchitecture, osteoblast function, abnormal bone turnover, and diminished biomechanical properties of bone.

SUMMARY

Mouse models have provided significant insights into the underlying mechanisms involved in the abnormalities of bone observed in T1D in humans. These translational models have provided targets and pathways that may be modifiable to prevent skeletal complications of T1D.

Association of plasma neutrophil gelatinase-associated lipocalin and thoracic aorta calcification in maintenance hemodialysis patients with and without diabetes

Background

Neutrophil gelatinase-associated lipocalin (NGAL) is not only a bone-derived factor involved in metabolism, but also a biomarker of kidney disease and cardiovascular pathophysiology. We conducted this cross-sectional observational study to explore relationships between plasma NGAL and thoracic aorta calcification (TAC) in maintenance hemodialysis (MHD) patients with and without diabetes.

Methods

Plasma NGAL was measured by ELISA, TAC was evaluated via computed tomography scan using a 3D quantification method or chest radiography aortic arch calcification score. Spearman correlation, Logistic regression and Partial correlation analysis were used to describe the correlations between NGAL and TAC.

Results

Plasma NGAL levels were lower in MHD patients with diabetes compared to those without diabetes (49.33(42.37, 55.48) vs 56.78(44.37, 674.13) ng/mL, P = 0.026). In MHD patients without diabetes, lg (NGAL) was positively correlated with ARC value(R = 0.612, P = 0.003) analyzed by Spearman correlation; for partial correlation analysis, lg (NGAL) was positively correlated with ARC value, after adjusting for age and sex (R = 0.550, P = 0.015), adjusting for age, sex and CHD (R = 0.565, P = 0.015), adjusting for age, sex, CHD and Alb (R = 0.536, P = 0.027), or adjusting for age, sex, CHD, Alb, and dialyzer membrane (polysulfone) (R = 0.590, P = 0.016); however, when adjusting for age, sex, CHD, Alb and Ca, the correlation between lg (NGAL) and ARC value disappeared. Positive correlation were found between NGAL and Ca (R = 0.644, P < 0.001), Ca and ACR (R = 0.534, P = 0.013) in Spearman coefficient analysis.

Conclusion

There were positive correlations among plasma NGAL, serum Ca and ARC in MHD patients without diabetes; which suggests that NGAL is possibly a participant in cardiovascular calcification, in non-diabetic MHD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02773-z.

Bone fragility in diabetes: novel concepts and clinical implications

Increased fracture risk represents an emerging and severe complication of diabetes. The resulting prolonged immobility and hospitalisations can lead to substantial morbidity and mortality. In type 1 diabetes, bone mass and bone strength are reduced, resulting in up to a five-times greater risk of fractures throughout life. In type 2 diabetes, fracture risk is increased despite a normal bone mass. Conventional dual-energy x-ray absorptiometry might underestimate fracture risk, but can be improved by applying specific adjustments. Bone fragility in diabetes can result from cellular abnormalities, matrix interactions, immune and vascular changes, and musculoskeletal maladaptation to chronic hyperglycaemia. This Review summarises how the bone microenvironment responds to type 1 and type 2 diabetes, and the mechanisms underlying fragility fractures. We describe the value of novel imaging technologies and the clinical utility of biomarkers, and discuss current and future therapeutic approaches that protect bone health in people with diabetes.

Protective effects of low-magnitude high-frequency vibration on high glucose-induced osteoblast dysfunction and bone loss in diabetic rats

Objective

Low-magnitude high-frequency vibration (LMHFV) has been reported to be capable of promoting osteoblast proliferation and differentiation. Reduced osteoblast activity and impaired bone formation were related to diabetic bone loss. We investigated the potential protective effects of LMHFV on high-glucose (HG)-induced osteoblasts in this study. In addition, the assessment of LMHFV treatment for bone loss attributed to diabetes was also performed in vivo.

Method

MC3T3-E1 cells induced by HG only or treated with LMHFV were treated in vitro. The experiments performed in this study included the detection of cell proliferation, migration and differentiation, as well as protein expression. Diabetic bone loss induced by streptozotocin (STZ) in rats was established. Combined with bone morphometric, microstructure, biomechanical properties and matrix composition tests, the potential of LMHFV in treating diabetes bone loss was explored.

Results

After the application of LMHFV, the inhibiting effects of HG on the proliferation, migration and differentiation of osteoblasts were alleviated. The GSK3β/β-catenin pathway was involved in the protective effect of LMHFV. Impaired microstructure and biomechanical properties attributed to diabetes were ameliorated by LMHFV treatment. The improvement of femur biomechanical properties might be associated with the alteration of the matrix composition by the LMHFV.

Conclusion

LMHFV exhibited a protective effect on osteoblasts against HG by regulating the proliferation, migration and differentiation of osteoblasts. The function of promoting bone formation and reinforcing bone strength made it possible for LMHFV to alleviate diabetic bone loss.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02803-w.