Premature chondrocyte apoptosis and compensatory upregulation of chondroregulatory protein expression in the growth plate of Goto-Kakizaki diabetic rats

Relationship between autophagy and NLRP3 inflammasome during articular cartilage degradation in oestrogen-deficient rats with streptozotocin-induced diabetes

BACKGROUND

Estrogen deficiency and Diabetes mellitus (DM) cause joint tissue deterioration, although the mechanisms are uncertain. This study evaluated the immunoexpression of autophagy and NLRP3-inflammasome markers, in rat articular cartilage with estrogen deficiency and DM.

METHODS

Twenty rats were sham-operated (SHAM) or ovariectomized (OVX) and equally allocated into four groups: SHAM and OVX groups administered with vehicle solution; SHAM and OVX groups treated with 60 mg/kg/body weight of streptozotocin, intraperitoneally, to induce DM (SHAM-DM and OVX-DM groups). After seven weeks, the rats were euthanized, and their joint knees were processed for paraffin embedding. Sections were stained with haematoxylin-eosin, toluidine blue, safranin-O/fast-green or subjected to picrosirius-red-polarisation method; immunohistochemistry to detect beclin-1 and microtubule-associated protein 1B-light chain 3 (autophagy markers), NLRP3 and interleukin-1β (IL-1β) (inflammasome activation markers), along with matrix metalloproteinase-9 (MMP-9), Nuclear factor-kappa B (NFκB), and Vascular endothelial growth factor A (VEGF-A) were performed.

RESULTS

Deterioration of articular cartilage and subchondral bone were greater in SHAM-DM and OVX-DM groups. Higher percentages of immunolabeled chondrocytes to NLRP3, IL-1β, MMP-9, NFκB, and VEGF-A, as well as lower percentages of chondrocytes immunolabeled to autophagy markers, were noticed in estrogen-deficient and diabetic groups. These differences were greater in the OVX-DM group. Percentages of immunolabeled chondrocytes showed negative correlation between autophagy markers v.s IL-1β, NLRP-3, MMP-9, NFκB, and VEGF-A, along with positive correlation between VEGF-A vs. MMP-9, NFκB, IL-1β, and NLRP3, and MMP-9 vs. NFκB.

CONCLUSIONS

In conclusion, autophagy reduction and NLRP3 inflammasome activation in chondrocytes may be implicated in articular cartilage degradation, under estrogen-deficient and DM conditions. Moreover, the combination of estrogen deficiency and DM may potentiate those effects.

Insulin Therapy on Bone Macroscopic, Microarchitecture, and MechanicalProperties of Tibia in Diabetic Rats

BACKGROUND

This study evaluated tibia's macroscopic structure, mechanical properties, and bone microarchitecture in rats with type 1 diabetes mellitus (T1DM).

METHODS

Eighteen animals were divided into three groups (n=6): Non-diabetic (ND), diabetic (D), and diabetic+insulin (DI). T1DM was induced by streptozotocin; insulin was administered daily (4IU). The animals were euthanized 35 days after induction. The tibiae were removed and analyzed using macroscopic, micro-computed tomography (micro-CT) and three-point bending. The macroscopic analysis measured proximal-distal length (PD), antero-posterior thickness (AP) of proximal (AP-P) and distal (AP-D) epiphysis, and lateral-medial thickness (LM) of proximal (LM-P) and distal (LM-D) epiphysis. Micro-CT analysis closed porosity, tissue mineral density, and cortical thickness. The three-point bending test measured maximum strength, energy, and stiffness.

RESULTS

The macroscopic analysis showed that D presented smaller measures of length and thickness (AP and AP-P) than ND and DI. More extensive measurements were observed of LM and AP-D thickness in DI than in D. In micro-CT, DI showed larger cortical thickness than D. Mechanical analysis showed lower strength in D than in other groups.

CONCLUSIONS

T1DM reduces bone growth and mechanical strength. Insulin therapy in diabetic rats improved bone growth and fracture resistance, making diabetic bone similar to normoglycemic animals.

Reduced Bone Regeneration in Rats With Type 2 Diabetes Mellitus as a Result of Impaired Stromal Cell and Osteoblast Function-A Computer Modeling Study

Bone has the fascinating ability to self-regenerate. However, under certain conditions, such as type 2 diabetes mellitus (T2DM), this ability is impaired. T2DM is a chronic metabolic disease known by the presence of elevated blood glucose levels that is associated with reduced bone regeneration capability, high fracture risk, and eventual non-union risk after a fracture. Several mechanical and biological factors relevant to bone regeneration have been shown to be affected in a diabetic environment. However, whether impaired bone regeneration in T2DM can be explained due to mechanical or biological alterations remains unknown. To elucidate the relevance of either one, the aim of this study was to investigate the relative contribution of T2DM-related alterations on either cellular activity or mechanical stimuli driving bone regeneration. A previously validated in silico computer modeling approach that was capable of explaining bone regeneration in uneventful conditions of healing was further developed to investigate bone regeneration in T2DM. Aspects analyzed included the presence of mesenchymal stromal cells (MSCs), cellular migration, proliferation, differentiation, apoptosis, and cellular mechanosensitivity. To further verify the computer model findings against in vivo data, an experimental setup was replicated, in which regeneration was compared in healthy and diabetic after a rat femur bone osteotomy stabilized with plate fixation. We found that mechanical alterations had little effect on the reduced bone regeneration in T2DM and that alterations in MSC proliferation, MSC migration, and osteoblast differentiation had the highest effect. In silico predictions of regenerated bone in T2DM matched qualitatively and quantitatively those from ex vivo μCT at 12 weeks post-surgery when reduced cellular activities reported in previous in vitro and in vivo studies were included in the model. The presented findings here could have clinical implications in the treatment of bone fractures in patients with T2DM. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Insulin does not rescue cortical and trabecular bone loss in type 2 diabetic Goto-Kakizaki rats

In type 2 diabetes mellitus (T2DM), the decreased bone strength is often associated with hyperglycemia and bone cell insulin resistance. Since T2DM is increasingly reported in young adults, it is not known whether the effect of T2DM on bone would be different in young adolescents and aging adults. Here, we found shorter femoral and tibial lengths in 7-month, but not 13-month, Goto-Kakizaki (GK) T2DM rats as compared to wild-type rats. Bone µCT analysis showed long-lasting impairment of both cortical and trabecular bones in GK rats. Although insulin treatment effectively improved hyperglycemia, it was not able to rescue trabecular BMD and cortical thickness in young adult GK rats. In conclusion, insulin treatment and alleviation of hyperglycemia did not increase BMD of osteopenic GK rats. It is likely that early prevention of insulin resistance should prevail over treatment of full-blown T2DM-related osteopathy.

Derangement of calcium metabolism in diabetes mellitus: negative outcome from the synergy between impaired bone turnover and intestinal calcium absorption

Both types 1 and 2 diabetes mellitus (T1DM and T2DM) are associated with profound deterioration of calcium and bone metabolism, partly from impaired intestinal calcium absorption, leading to a reduction in calcium uptake into the body. T1DM is associated with low bone mineral density (BMD) and osteoporosis, whereas the skeletal changes in T2DM are variable, ranging from normal to increased and to decreased BMD. However, both types of DM eventually compromise bone quality through production of advanced glycation end products and misalignment of collagen fibrils (so-called matrix failure), thereby culminating in a reduction of bone strength. The underlying cellular mechanisms (cellular failure) are related to suppression of osteoblast-induced bone formation and bone calcium accretion, as well as to enhancement of osteoclast-induced bone resorption. Several other T2DM-related pathophysiological changes, e.g., osteoblast insulin resistance, impaired productions of osteogenic growth factors (particularly insulin-like growth factor 1 and bone morphogenetic proteins), overproduction of pro-inflammatory cytokines, hyperglycemia, and dyslipidemia, also aggravate diabetic osteopathy. In the kidney, DM and the resultant hyperglycemia lead to calciuresis and hypercalciuria in both humans and rodents. Furthermore, DM causes deranged functions of endocrine factors related to mineral metabolism, e.g., parathyroid hormone, 1,25-dihydroxyvitamin D3, and fibroblast growth factor-23. Despite the wealth of information regarding impaired bone remodeling in DM, the long-lasting effects of DM on calcium metabolism in young growing individuals, pregnant women, and neonates born to women with gestational DM have received scant attention, and their underlying mechanisms are almost unknown and worth exploring.