Runt-related transcription factor 2 (RUNX2) and RUNX2-related osteogenic genes are down-regulated throughout osteogenesis in type 1 diabetes mellitus

Bone Marrow Adipose Tissue

Bone marrow (BM) acts as a dynamic organ within the bone cavity, responsible for hematopoiesis, skeletal remodeling, and immune system control. Bone marrow adipose tissue (BMAT) was long simply considered a filler of space, but now it is known that it instead constitutes an essential element of the BM microenvironment that participates in homeostasis, influences bone health and bone remodeling, alters hematopoietic stem cell functions, contributes to the commitment of mesenchymal stem cells, provides effects to immune homeostasis and defense against infections, and participates in energy metabolism and inflammation. BMAT has emerged as a significant contributor to the development and progression of various diseases, shedding light on its complex relationship with health. Notably, BMAT has been implicated in metabolic disorders, hematological malignancies, and skeletal conditions. BMAT has been shown to support the proliferation of tumor cells in acute myeloid leukemia and niche adipocytes have been found to protect cancer cells against chemotherapy, contributing to treatment resistance. Moreover, BMAT's impact on bone density and remodeling can lead to conditions like osteoporosis, where high levels of BMAT are inversely correlated with bone mineral density, increasing the risk of fractures. BMAT has also been associated with diabetes, obesity, and anorexia nervosa, with varying effects on individuals depending on their weight and health status. Understanding the interaction between adipocytes and different diseases may lead to new therapeutic strategies.

Bone Structure and Turnover in Postmenopausal Women With Long-Standing Type 1 Diabetes

Compromised bone structural and mechanical properties are implicated in the increased fracture risk in type 1 diabetes (T1D). We investigated bone structure and turnover by histomorphometry in postmenopausal women with T1D and controls without diabetes using tetracycline double-labeled transiliac bone biopsy. After in vivo tetracycline double labeling, postmenopausal women with T1D of at least 10 years and without diabetes underwent transiliac bone biopsy. An expert blinded to the study group performed histomorphometry. Static and dynamic histomorphometry measurements were performed and compared between the two groups. The analysis included 9 postmenopausal women with T1D (mean age 58.4 ± 7.1 years with 37.9 ± 10.9 years of diabetes and HbA1c 7.1% ± 0.4%) and 7 postmenopausal women without diabetes (mean age 60.9 ± 3.3 years and HbA1c 5.4% ± 0.2%). There were no significant differences in serum PTH (38.6 ± 8.1 versus 51.9 ± 23.9 pg/mL), CTX (0.4 ± 0.2 versus 0.51 ± 0.34 ng/mL), or P1NP (64.5 ± 26.2 versus 87.3 ± 45.3 ng/mL). Serum 25-hydroxyvitamin D levels were higher in T1D than in controls (53.1 ± 20.8 versus 30.9 ± 8.2 ng/mL, p < 0.05). Bone structure metrics (bone volume, trabecular thickness, trabecular number, and cortical thickness) were similar between the groups. Indices of bone formation (osteoid volume, osteoid surface, and bone formation rate) were 40% lower in T1D and associated with lower activation frequency. However, the differences in bone formation were not statistically significant. Long-standing T1D may affect bone turnover, mainly bone formation, without significantly affecting bone structure. Further research is needed to understand bone turnover and factors affecting bone turnover in people with T1D. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

The complex pathophysiology of bone fragility in obesity and type 2 diabetes mellitus: therapeutic targets to promote osteogenesis

Fractures associated with Type2 diabetes (T2DM) are major public health concerns in an increasingly obese and aging population. Patients with obesity or T2DM have normal or better than normal bone mineral density but at an increased risk for fractures. Hence it is crucial to understand the pathophysiology and mechanism of how T2DM and obesity result in altered bone physiology leading to increased fracture risk. Although enhanced osteoclast mediated bone resorption has been reported for these patients, the most notable observation among patients with T2DM is the reduction in bone formation from mostly dysfunction in osteoblast differentiation and survival. Studies have shown that obesity and T2DM are associated with increased adipogenesis which is most likely at the expense of reduced osteogenesis and myogenesis considering that adipocytes, osteoblasts, and myoblasts originate from the same progenitor cells. Furthermore, emerging data point to an inter-relationship between bone and metabolic homeostasis suggesting that these physiologic processes could be under the control of common regulatory pathways. Thus, this review aims to explore the complex mechanisms involved in lineage differentiation and their effect on bone pathophysiology in patients with obesity and T2DM along with an examination of potential novel pharmacological targets or a re-evaluation of existing drugs to improve bone homeostasis.

Probable Treatment Targets for Diabetic Retinopathy Based on an Integrated Proteomic and Genomic Analysis

Purpose

Using previously approved medications for new indications can expedite the lengthy and expensive drug development process. We describe a bioinformatics pipeline that integrates genomics and proteomics platforms to identify already-approved drugs that might be useful to treat diabetic retinopathy (DR).

Methods

Proteomics analysis of vitreous humor samples from 12 patients undergoing pars plana vitrectomy for DR and a whole genome dataset (UKBiobank TOPMed-imputed) from 1330 individuals with DR and 395,155 controls were analyzed independently to identify biological pathways associated with DR. Common biological pathways shared between both datasets were further analyzed (STRING and REACTOME analyses) to identify target proteins for probable drug modulation. Curated target proteins were subsequently analyzed by the BindingDB database to identify chemical compounds they interact with. Identified chemical compounds were further curated through the Expasy SwissSimilarity database for already-approved drugs that interact with target proteins.

Results

The pathways in each dataset (proteomics and genomics) converged in the upregulation of a previously unknown pathway involved in DR (RUNX2 signaling; constituents MMP-13 and LGALS3), with an emphasis on its role in angiogenesis and blood-retina barrier. Bioinformatics analysis identified U.S. Food and Drug Administration (FDA)-approved medications (raltitrexed, pemetrexed, glyburide, probenecid, clindamycin hydrochloride, and ticagrelor) that, in theory, may modulate this pathway.

Conclusions

The bioinformatics pipeline described here identifies FDA-approved drugs that can be used for new alternative indications. These theoretical candidate drugs should be validated with experimental studies.

Translational Relevance

Our study suggests possible drugs for DR treatment based on an integrated proteomics and genomics pipeline. This approach can potentially expedite the drug discovery process by identifying already-approved drugs that might be used for new indications.

Skeletal manifestations in a streptozotocin-induced C57BL/6 model of Type 1 diabetes

Diabetes Mellitus is a metabolic disease which profoundly affects many organ systems in the body, including the skeleton. As is often the case with biology, there are inherent differences between the sexes when considering skeletal development and disease progression and outcome. Therefore, the aim of this study was to develop a protocol to reliably induce diabetes in both sexes of the C57BL/6 mouse utilizing streptozotocin (STZ) and to characterize the resulting bone phenotype. We hypothesized that destruction of the β-cells in the pancreatic islet by STZ would result in a diabetic state with downstream skeletal manifestations. Beginning at 8 weeks of age, mice were injected for 5 consecutive days with STZ (65 mg/kg males, 90 mg/kg females) dissolved in a citrate buffer. The diabetic state of the mice was monitored for 5 weeks to ensure persistent hyperglycemia and mice were euthanized at 15 weeks of age. Diabetes was confirmed through blood glucose monitoring, glucose and insulin tolerance testing, HbA1c measurement, and histological staining of the pancreas. The resulting bone phenotype was characterized using microcomputed tomography to assess bone structure, and whole bone mechanical testing to assess bone functional integrity. Mice from both sexes experienced loss of β-cell mass and increased glycation of hemoglobin, as well as reduced trabecular thickness and trabecular tissues mineral density (TMD), and reduced cortical thickness and cortical bone area fraction. In female mice the change area fraction was driven by a reduction in overall bone size while in male mice, the change was driven by increased marrow area. Males also experienced reduced cortical TMD. Mechanical bending tests of the tibiae showed significant results in females with a reduction in yield force and ultimate force driving lower work to yield and total work and a roughly 40 % reduction of stiffness. When tissue level parameters were estimated using beam theory, there was a significant reduction in yield and ultimate stresses as well as elastic modulus. The previously reported mechanistic similarity in the action of STZ on murine animals, as well as the ease of STZ administration via IP injection make this model is a strong candidate for future exploration of osteoporotic bone disease, Diabetes Mellitus, and the link between estrogen and glucose sensitivity.

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.

Bone Remodeling in Mandible of Wistar Rats with Diabetes Mellitus and Osteoporosis

OBJECTIVES

 This study aimed to determine some of bone molecular expressions and its possible bone remodeling pathway between diabetes mellitus (DM) and osteoporosis model in the mandibular bone of Wistar rats.

MATERIALS AND METHODS

 Twenty-seven female Wistar rats were divided randomly into control and treatment groups. Treatment groups were injected with streptozotocin intraperitoneally to induce DM (P1) and underwent bilateral ovariectomy to generate osteoporosis (P2). All groups were terminated after 12 weeks. Immunohistochemical and hematoxylin-eosin staining were performed to determine the expression of Runt-related transcription factor 2 (RUNX2), Osterix, vascular endothelial growth factor (VEGF), receptor activator of nuclear factor κB ligand (RANKL), osteoprotegerin (OPG), tartrate-resistant acid phosphatase (TRAP), and observed the osteoblast and osteoclast. Statistical analysis was performed using one-way analysis of variance.

RESULTS

 The lowest mean of RUNX2 and VEGF expression was found in the P2 group. The lowest mean of Osterix expression was found in the P1 group. Both P1 and P2 groups of osteoblast/osteoclast ratio were decreased. There were no significant differences in the expression of TRAP between all groups; however, increased expression of RANKL/OPG ratio was only found in the P2 group.

CONCLUSION

 DM and osteoporosis induce changes in the bone remodeling pathway which are represented by a decrease in osteoblast biomarkers and an increase in osteoclast biomarkers.

Role of nitric oxide in type 1 diabetes-induced osteoporosis

Type 1 diabetes (T1D)-induced osteoporosis is characterized by decreased bone mineral density, bone quality, rate of bone healing, bone formation, and increased bone resorption. Patients with T1D have a 2-7-fold higher risk of osteoporotic fracture. The mechanisms leading to increased risk of osteoporotic fracture in T1D include insulin deficiency, hyperglycemia, insulin resistance, lower insulin-like growth factor-1, hyperglycemia-induced oxidative stress, and inflammation. In addition, a higher probability of falling, kidney dysfunction, weakened vision, and neuropathy indirectly increase the risk of osteoporotic fracture in T1D patients. Decreased nitric oxide (NO) bioavailability contributes to the pathophysiology of T1D-induced osteoporotic fracture. This review discusses the role of NO in osteoblast-mediated bone formation and osteoclast-mediated bone resorption in T1D. In addition, the mechanisms involved in reduced NO bioavailability and activity in type 1 diabetic bones as well as NO-based therapy for T1D-induced osteoporosis are summarized. Available data indicates that lower NO bioavailability in diabetic bones is due to disruption of phosphatidylinositol 3‑kinase/protein kinase B/endothelial NO synthases and NO/cyclic guanosine monophosphate/protein kinase G signaling pathways. Thus, NO bioavailability may be boosted directly or indirectly by NO donors. As NO donors with NO-like effects in the bone, inorganic nitrate and nitrite can potentially be used as novel therapeutic agents for T1D-induced osteoporosis. Inorganic nitrites and nitrates can decrease the risk for osteoporotic fracture probably directly by decreasing osteoclast activity, decreasing fat accumulation in the marrow cavity, increasing osteoblast activity, and increasing bone perfusion or indirectly, by improving hyperglycemia, insulin resistance, and reducing body weight.

Diabetes impairs fracture healing through disruption of cilia formation in osteoblasts

Diabetes-associated fracture risk and impaired fracture healing represents a serious health threat. It is well known that type 1 diabetes mellitus (T1DM) impairs fracture healing due to its effect on osteoblasts and their progenitor cells. Previous studies have showed that primary cilia and intraflagellar transport protein 80 (IFT80) are critical for bone formation. However, whether TIDM impairs fracture healing due to influencing ciliary gene expression and cilia formation is unknown. Here, we investigated the effect of T1DM on primary cilia in a streptozotocin induced diabetes mouse model and examined the impact of cilia on fracture healing in osteoblasts by deletion of IFT80 in osteoblast linage using osterix (OSX)-cre (OSXcretTAIFT80f/f). The results showed that diabetes inhibited ciliary gene expression and primary cilia formation to an extent that was similar to normoglycemic mice with IFT80 deletion. Moreover, diabetic mice and normoglycemic mice with cilia loss in osteoblasts (OSXcretTAIFT80f/f) both exhibited delayed fracture healing with significantly reduced bone density and mechanical strength as well as with reduced expression of osteoblast markers, decreased angiogenesis and proliferation of bone lining cells at the fracture sites. In vitro studies showed that advanced glycation end products (AGEs) downregulated IFT80 expression in osteoblast progenitors. Moreover, AGEs and IFT80 deletion significantly reduced cilia number and length which inhibited differentiation of primary osteoblast precursors. Thus, this study for the first time report that primary cilia are essential for bone regeneration during fracture healing and loss of cilia caused by diabetes in osteoblasts resulted in defective diabetic fracture healing.

Streptozotocin-Induced Diabetes in a Mouse Model (BALB/c) Is Not an Effective Model for Research on Transplantation Procedures in the Treatment of Type 1 Diabetes

Type 1 diabetes (T1D) is characterized by the destruction of over 90% of the β-cells. C-peptide is a parameter for evaluating T1D. Streptozotocin (STZ) is a standard method of inducing diabetes in animals. Eight protocols describe the administration of STZ in mice; C-peptide levels are not taken into account. The aim of the study is to determine whether the STZ protocol for the induction of beta-cell mass destruction allows for the development of a stable in vivo mouse model for research into new transplant procedures in the treatment of type 1 diabetes. Materials and methods: Forty BALB/c mice were used. The animals were divided into nine groups according to the STZ dose and a control group. The STZ doses were between 140 and 400 mg/kg of body weight. C-peptide was taken before and 2, 7, 9, 12, 14, and 21 days after STZ. Immunohistochemistry was performed. The area of the islet and insulin-/glucagon-expressing tissues was calculated. Results: Mice who received 140, 160, 2 × 100, 200, and 250 mg of STZ did not show changes in mean fasting C-peptide in comparison to the control group and to day 0. All animals with doses of 300 and 400 mg of STZ died during the experiment. The area of the islets did not show any differences between the control and STZ-treated mice in groups below 300 mg. The reduction of insulin-positive areas in STZ mice did not exceed 50%. Conclusions: Streptozotocin is not an appropriate method of inducing a diabetes model for further research on transplantation treatments of type 1 diabetes, having caused the destruction of more than 90% of the β-cell mass in BALB/c mice.

Phosphate and fibroblast growth factor 23 in diabetes

Diabetes is associated with a strongly elevated risk of cardiovascular disease, which is even more pronounced in patients with diabetic nephropathy. Currently available guideline-based efforts to correct traditional risk factors are only partly able to attenuate this risk, underlining the urge to identify novel treatment targets. Emerging data point towards a role for disturbances in phosphate metabolism in diabetes. In this review, we discuss the role of phosphate and the phosphate-regulating hormone fibroblast growth factor 23 (FGF23) in diabetes. We address deregulations of phosphate metabolism in patients with diabetes, including diabetic ketoacidosis. Moreover, we discuss potential adverse consequences of these deregulations, including the role of deregulated phosphate and glucose as drivers of vascular calcification propensity. Finally, we highlight potential treatment options to correct abnormalities in phosphate and FGF23. While further studies are needed to more precisely assess their clinical impact, deregulations in phosphate and FGF23 are promising potential target in diabetes and diabetic nephropathy.

Mechanisms of altered bone remodeling in children with type 1 diabetes

Bone loss associated with type 1 diabetes mellitus (T1DM) begins at the onset of the disease, already in childhood, determining a lower bone mass peak and hence a greater risk of osteoporosis and fractures later in life. The mechanisms underlying diabetic bone fragility are not yet completely understood. Hyperglycemia and insulin deficiency can affect the bone cells functions, as well as the bone marrow fat, thus impairing the bone strength, geometry, and microarchitecture. Several factors, like insulin and growth hormone/insulin-like growth factor 1, can control bone marrow mesenchymal stem cell commitment, and the receptor activator of nuclear factor-κB ligand/osteoprotegerin and Wnt-b catenin pathways can impair bone turnover. Some myokines may have a key role in regulating metabolic control and improving bone mass in T1DM subjects. The aim of this review is to provide an overview of the current knowledge of the mechanisms underlying altered bone remodeling in children affected by T1DM.

Role of osteogenic Dickkopf-1 in bone remodeling and bone healing in mice with type I diabetes mellitus

Type 1 diabetes mellitus (T1DM) is associated with low bone mass and a higher risk for fractures. Dickkopf-1 (Dkk1), which inhibits Wnt signaling, osteoblast function, and bone formation, has been found to be increased in the serum of patients with T1DM. Here, we investigated the functional role of Dkk1 in T1DM-induced bone loss in mice. T1DM was induced in 10-week-old male mice with Dkk1-deficiency in late osteoblasts/osteocytes (Dkk1^f/f;Dmp1-Cre, cKO) and littermate control mice by 5 subsequent injections of streptozotocin (40 mg/kg). Age-matched, non-diabetic control groups received citrate buffer instead. At week 12, calvarial defects were created in subgroups of each cohort. After a total of 16 weeks, weight, fat, the femoral bone phenotype and the area of the bone defect were analyzed using µCT and dynamic histomorphometry. During the experiment, diabetic WT and cKO mice did not gain body weight compared to control mice. Further they lost their perigonadal and subcutaneous fat pads. Diabetic mice had highly elevated serum glucose levels and impaired glucose tolerance, regardless of their Dkk1 levels. T1DM led to a 36% decrease in trabecular bone volume in Cre− negative control animals, whereas Dkk1 cKO mice only lost 16%. Of note, Dkk1 cKO mice were completely protected from T1DM-induced cortical bone loss. T1DM suppressed the bone formation rate, the number of osteoblasts at trabecular bone, serum levels of P1NP and bone defect healing in both, Dkk1-deficient and sufficient, mice. This may be explained by increased serum sclerostin levels in both genotypes and the strict dependence on bone formation for bone defect healing. In contrast, the number of osteoclasts and TRACP 5b serum levels only increased in diabetic control mice, but not in Dkk1 cKO mice. In summary, Dkk1 derived from osteogenic cells does not influence the development of T1DM but plays a crucial role in T1DM-induced bone loss in male mice by regulating osteoclast numbers.

Association of type 2 diabetes mellitus and periodontal disease susceptibility with genome-wide association-identified risk variants in a Southeastern Brazilian population

OBJECTIVE

Genome-wide association studies (GWAS) and literature have identified polymorphisms in the KCNJ11, HNF1A, IRS1, TCF7L2, CDKAL1, CDKN2B, RPSAP52, GPR45 HHEX, IL18, and RUNX2 genes associated with type 2 diabetes mellitus (T2DM) and/or periodontitis (P) in diverse populations, and we sought to evaluate them as genetic risk variants for these diseases in the Brazilian population.

MATERIAL AND METHODS

Periodontal, glycemic, and lipid data were obtained from 931 individuals divided into: control (n = 334), periodontitis (P; n = 358), and periodontitis associated with T2DM (P + T2DM; n = 239). After genotyping, associations between polymorphisms and pathologies were tested by multiple logistic and linear regressions, adjusting for age, sex, and smoking habits.

RESULTS

Considering the studied subjects, the increased risk to develop periodontitis in the periodontitis P + T2DM group was found for HNF1A-rs7957197-TA, CDKAL1-rs7754840-CG, RPSAP52-rs1531343-GC, TCF7L2-rs7903146-TT, and CDKN2B-rs7018475-GG. The association of these genetic variants for TCF7L2 and CDKN2B was confirmed for female, never smokers, and poorly controlled P + T2DM. CDKN2B-rs7018475 was associated with worse glycemic condition and periodontal parameters.

CONCLUSION

These five reported genetic variants were associated in the studied Southeastern Brazilian population as genetic risk variants of periodontitis and T2DM associated to periodontitis as comorbidity. Gene-phenotype associations with sex and smoking habits and the CDKN2B-rs7018475 with the poor glycemic control and more severe periodontal conditions should be further investigated.

CLINICAL RELEVANCE

Polymorphisms in the CDKAL1-rs7754840, HNF1A-rs7957197, RPSAP52-rs1531343, TCF7L2-rs7903146, and CDKN2B-rs7018475 might predispose to periodontitis and T2DM associated with periodontitis. These findings may be useful in public health genomics and future advanced clinical practice, since genetic carriage can be measured before disease onset, being of potential great benefit for treatment planning and prognosis in early disease stages.

Liraglutide Inhibits Osteoclastogenesis and Improves Bone Loss by Downregulating Trem2 in Female Type 1 Diabetic Mice: Findings From Transcriptomics

BACKGROUND

The mechanisms of bone fragility in type 1 diabetes (T1D) are not fully understood. Whether glucagon-like peptide-1 receptor (GLP-1R) agonists could improve bone quality in T1D context also remains elusive.

AIMS

We aimed to explore the possible mechanisms of bone loss in T1D and clarify whether liraglutide has effects on bone quality of T1D mice using transcriptomics.

METHODS

Female streptozotocin-induced diabetic C57BL/6J mice were randomly divided into four groups and received the following treatments daily for 8 weeks: saline as controls, insulin, liraglutide, and liraglutide combined with insulin. These groups were also compared with non-STZ-treated normal glucose tolerance (NGT) group. Trunk blood and bone tissues were collected for analysis. Three tibia from each of the NGT, saline-treated, and liraglutide-treated groups were randomly selected for transcriptomics.

RESULTS

Compared with NGT mice, saline-treated T1D mice manifested markedly hyperglycemia and weight loss, and micro-CT revealed significantly lower bone mineral density (BMD) and deficient microarchitectures in tibias. Eight weeks of treatment with liraglutide alone or combined with insulin rescued the decreased BMD and partly corrected the compromised trabecular microarchitectures. Transcriptomics analysis showed there were 789 differentially expressed genes mainly mapped to osteoclastogenesis and inflammation pathways. The RT-qPCR verified that the gene expression of Trem2, Nfatc1, Trap, and Ctsk were significantly increased in the tibia of T1D compared with those in the NGT group. Liraglutide treatment alone or combined with insulin could effectively suppress osteoclastogenesis by downregulating the gene expression of Trem2, Nfatc1, Ctsk, and Trap.

CONCLUSIONS

Taken together, increased osteoclastogenesis with upregulated expression of Trem2 played an important role in bone loss of T1D mice. Liraglutide provided protective effects on bone loss in T1D mice by suppressing osteoclastogenesis.

Doxycycline restores the impaired osteogenic commitment of diabetic-derived bone marrow mesenchymal stromal cells by increasing the canonical WNT signaling

Diabetes mellitus comprehends a group of chronic metabolic disorders, associated with damage and dysfunction of distinct tissues, including bone. At the cellular level, an impaired osteoblastogenesis has been reported, affecting the viability, proliferation and functionality of osteoblasts and precursor populations, hampering the bone metabolic activity, remodeling and healing. Tetracyclines embrace a group of broad-spectrum antibacterial compounds with potential anabolic effects on the bone tissue, through antibacterial-independent mechanisms. Accordingly, this study aims to address the modulatory capability and associated molecular signaling of a low dosage doxycycline - a semi-synthetic tetracycline, in the functional activity of osteoblastic progenitor cells (bone marrow-derived mesenchymal stromal cells), established from a translational diabetic experimental model. Bone marrow-derived mesenchymal stromal cells were isolated from streptozotocin-induced diabetic Wistar rat with proven osteopenia. Cultures were characterized, in the presence of doxycycline (1 μg ml^-1) for proliferation, metabolic activity, apoptosis, collagen synthesis and relevant gene expression with the osteogenic and adipogenic program. The activation of the Wnt/β-catenin pathway was further detailed. Doxycycline normalized the viability, proliferation and metabolic activity of the established cultures, further decreasing cell apoptosis, to levels similar to control. The addition of this drug to the culture environment further increased the osteogenic activation, upregulating the expression of osteogenic markers and collagen synthesis, at the same time that a decreased adipogenic priming was attained. These processes were found to me mediated, at least in part, by the restoration of the signaling through the Wnt/β-catenin pathway.

Transcutaneous CO2 application accelerates fracture repair in streptozotocin-induced type I diabetic rats

INTRODUCTION

Diabetes mellitus (DM) negatively affects fracture repair by inhibiting endochondral ossification, chondrogenesis, callus formation, and angiogenesis. We previously reported that transcutaneous CO₂ application accelerates fracture repair by promoting endochondral ossification and angiogenesis. The present study aimed to determine whether CO₂ treatment would promote fracture repair in cases with type I DM.

RESEARCH DESIGN AND METHODS

A closed femoral shaft fracture was induced in female rats with streptozotocin-induced type I DM. CO₂ treatment was performed five times a week for the CO₂ group. Sham treatment, where CO₂ was replaced with air, was performed for the control group. Radiographic, histologic, genetic, and biomechanical measurements were taken at several time points.

RESULTS

Radiographic assessment demonstrated that fracture repair was induced in the CO₂ group. Histologically, accelerated endochondral ossification and capillary formation were observed in the CO₂ group. Immunohistochemical assessment indicated that early postfracture proliferation of chondrocytes in callus was enhanced in the CO₂ group. Genetic assessment results suggested that cartilage and bone formation, angiogenesis, and vasodilation were upregulated in the CO₂ group. Biomechanical assessment revealed enhanced mechanical strength in the CO₂ group.

CONCLUSIONS

Our findings suggest that CO₂ treatment accelerates fracture repair in type I DM rats. CO₂ treatment could be an effective strategy for delayed fracture repair due to DM.

Low Intensity Pulsed Ultrasound Therapy (LIPUS): A review of evidence and potential applications in diabetics

Low Intensity Pulsed Ultrasound Therapy (LIPUS) is a non-invasive treatment and aims to reduce fracture healing time and avoid non-union by delivering micro-mechanical stress to the bone to stimulate bone healing. In 2018, the National Institute for Health and Clinical Excellence (NICE) recommended that the evidence for LIPUS to promote healing of delayed-union and non-union fractures raised no major safety concerns, but the current evidence on efficacy is inadequate in quality. Little is known about the potential benefits of LIPUS for fracture healing in diabetic patients. In this article, we review the current evidence of LIPUS therapy both in animal and human studies and its possible application on fractures in diabetics.

Effects of estrogen deficiency followed by streptozotocin-induced diabetes on periodontal tissues of female rats

Although both estrogen deficiency and diabetes contribute to periodontal tissue deterioration, the combined effects of these conditions on periodontium is unknown. Thus, we analyzed the combined effects of ovariectomy followed by streptozotocin (STZ)-induced diabetes on periodontal tissues of rats. Twenty adult rats were ovariectomized (OVX) or SHAM-operated (SHAM). After 3 weeks, the rats received an intraperitoneal injection of STZ (60 mg/kg/body weight) to induce diabetes or vehicle (blank) solution. The groups were assigned as follows (n = 5): SHAM-vehicle (SHAM), OVX-vehicle (OVX), SHAM + STZ (SHAM-Di), and OVX + STZ (OVX-Di). Seven weeks post-diabetes induction, the rats were euthanized. Blood samples were collected for glucose measurements and maxillae were processed for paraffin embedding. Sections stained with hematoxylin/eosin, Masson's trichrome, and picrosirius-red were used for alveolar bone loss and collagen fiber analysis in the lamina propria. Immunohistochemistry was performed for runt-related transcription factor 2 (Runx2), matrix metalloproteinase 9 (MMP-9), and tryptase detection. Alveolar bone loss and fewer collagen fibers were observed in the OVX-Di group, collagen fibers with irregular organization, and MMP-9 immunoreactivity were more evident in diabetic groups, and MMP-9-positive osteoclasts on alveolar bone surface were noticed in all groups. The OVX-Di group showed lower Runx2 immunoreactivity (osteoblast formation marker), and more tryptase-positive cells (mast cell marker) in the alveolar bone marrow. Our results indicate that estrogen depletion, followed by STZ-induced diabetes, promotes periodontal tissue deterioration that is more evident than both interventions applied alone. Furthermore, our results points to a possible participation of bone-derived mast cells in this process.

Proteomic and Transcriptomic Approaches for Studying Bone Regeneration in Health and Systemically Compromised Conditions

Bone regeneration is a complex biological process, where the molecular mechanisms are only partially understood. In an ageing population, where the prevalence of chronic diseases with an impact on bone metabolism is increasing, it becomes crucial to identify new strategies that would improve regenerative outcomes also in medically compromised patients. In this context, omics are demonstrating a great potential, as they offer new insights on the molecular mechanisms regulating physiologic/pathologic bone healing and, at the same time, allow the identification of new diagnostic and therapeutic targets. This review provides an overview on the current evidence on the use of transcriptomic and proteomic approaches in bone regeneration research, particularly in relation to type 1 diabetes and osteoporosis, and discusses future scenarios and potential benefits and limitations on the integration of multi-omics. It is suggested that future research will leverage the synergy of omics with statistical modeling and bioinformatics to prompt the understanding of the biology underpinning bone formation in health and medically compromised conditions. With an eye toward personalized medicine, new strategies combining the mining of large datasets and bioinformatic data with a detailed characterization of relevant phenotypes will need to be pursued to further the understanding of disease mechanisms.

Insulin Enhances the In Vitro Osteogenic Capacity of Flexor Tendon-Derived Progenitor Cells

There is increased incidence of tendon disorders and decreased tendon healing capacity in people with diabetes mellitus (DM). Recent studies have also suggested pathological ossification in repair tendon of people with DM. Therefore, the objective of this study is to investigate the effects of insulin supplementation, an important pathophysiologic stimulus of DM, on tendon progenitor cell (TPC) proliferation and in vitro osteogenic capacity. Passage 3 TPCs were isolated from collagenase-digested, equine superficial digital flexor tendons. TPC proliferation was measured via MTT assay after 3 days of monolayer culture in medium supplemented with 0, 0.007, 0.07, and 0.7 nM insulin. In vitro osteogenic capacity of TPCs (Alizarin Red staining, osteogenic mRNA expression, and alkaline phosphatase bioactivity) was assessed with 0, 0.07, and 0.7 nM insulin-supplemented osteogenic induction medium. Insulin (0.7 nM) significantly increased TPC proliferation after 3 days of monolayer culture. Alizarin Red staining of insulin-treated TPC osteogenic cultures demonstrated robust cell aggregation and mineralized matrix secretion, in a dose-dependent manner. Runx2, alkaline phosphatase, and Osteonectin mRNA and alkaline phosphatase bioactivity of insulin-treated TPC cultures were significantly higher at day 14 of osteogenesis compared to untreated controls. Addition of picropodophyllin (PPP), a selective IGF-I receptor inhibitor, mitigated the increased osteogenic capacity of TPCs, indicating that IGF-I signaling plays an important role. Our findings indicate that hyperinsulinemia may alter TPC phenotype and subsequently impact the quality of repair tendon tissue.

Bone health in diabetes and prediabetes

Bone fragility has been recognized as a complication of diabetes, both type 1 diabetes (T1D) and type 2 diabetes (T2D), whereas the relationship between prediabetes and fracture risk is less clear. Fractures can deeply impact a diabetic patient’s quality of life. However, the mechanisms underlying bone fragility in diabetes are complex and have not been fully elucidated. Patients with T1D generally exhibit low bone mineral density (BMD), although the relatively small reduction in BMD does not entirely explain the increase in fracture risk. On the contrary, patients with T2D or prediabetes have normal or even higher BMD as compared with healthy subjects. These observations suggest that factors other than bone mass may influence fracture risk. Some of these factors have been identified, including disease duration, poor glycemic control, presence of diabetes complications, and certain antidiabetic drugs. Nevertheless, currently available tools for the prediction of risk inadequately capture diabetic patients at increased risk of fracture. Aim of this review is to provide a comprehensive overview of bone health and the mechanisms responsible for increased susceptibility to fracture across the spectrum of glycemic status, spanning from insulin resistance to overt forms of diabetes. The management of bone fragility in diabetic patient is also discussed.

Bone Morphogenetic Protein-6 Attenuates Type 1 Diabetes Mellitus-Associated Bone Loss

Patients with type 1 diabetes mellitus (T1DM) often suffer from osteopenia or osteoporosis. Although most agree that T1DM-induced hyperglycemia is a risk factor for progressive bone loss, the mechanisms for the link between T1DM and bone loss still remain elusive. In this study, we found that bone marrow-derived mesenchymal stem cells (BMSCs) isolated from T1DM donors were less inducible for osteogenesis than those from non-T1DM donors and further identified a mechanism involving bone morphogenetic protein-6 (BMP6) that was produced significantly less in BMSCs derived from T1DM donors than that in control cells. With addition of exogenous BMP6 in culture, osteogenesis of BMSCs from T1DM donors was restored whereas the treatment of BMP6 seemed not to affect non-T1DM control cells. We also demonstrated that bone mineral density (BMD) was reduced in streptozotocin-induced diabetic mice compared with that in control animals, and intraperitoneal injection of BMP6 mitigated bone loss and increased BMD in diabetic mice. Our results suggest that bone formation in T1DM patients is impaired by reduction of endogenous BMP6, and supplementation of BMP6 enhances osteogenesis of BMSCs to restore BMD in a mouse model of T1DM, which provides insight into the development of clinical treatments for T1DM-assocaited bone loss. Stem Cells Translational Medicine 2019;8:522-534.

Expression of calcification-related ion transporters during blue mussel larval development

The physiological processes driving the rapid rates of calcification in larval bivalves are poorly understood. Here, we use a calcification substrate-limited approach (low dissolved inorganic carbon, C T) and mRNA sequencing to identify proteins involved in bicarbonate acquisition during shell formation. As a secondary approach, we examined expression of ion transport and shell matrix proteins (SMPs) over the course of larval development and shell formation. We reared four families of Mytilus edulis under ambient (ca. 1865 µmol/kg) and low C T (ca. 941 µmol/kg) conditions and compared expression patterns at six developmental time points. Larvae reared under low C T exhibited a developmental delay, and a small subset of contigs was differentially regulated between ambient and low C T conditions. Of particular note was the identification of one contig encoding an anion transporter (SLC26) which was strongly upregulated (2.3-2.9 fold) under low C T conditions. By analyzing gene expression profiles over the course of larval development, we are able to isolate sequences encoding ion transport and SMPs to enhance our understanding of cellular pathways underlying larval calcification processes. In particular, we observe the differential expression of contigs encoding SLC4 family members (sodium bicarbonate cotransporters, anion exchangers), calcium-transporting ATPases, sodium/calcium exchangers, and SMPs such as nacrein, tyrosinase, and transcripts related to chitin production. With a range of candidate genes, this work identifies ion transport pathways in bivalve larvae and by applying comparative genomics to investigate temporal expression patterns, provides a foundation for further studies to functionally characterize the proteins involved in larval calcification.

Keratin scaffolds with human adipose stem cells: Physical and biological effects toward wound healing

Keratin, a natural biomaterial derived from wool or human hair, has the intrinsic ability to interact with different types of cells and the potential to serve as a controllable extracellular matrix that can be used a scaffold for tissue engineering. In this study, we demonstrated a simple and fast technique to construct 3D keratin scaffolds for accelerated wound healing using a lyophilization method based on extraction of keratin from human hair. The physical properties of the keratin scaffolds such as water uptake, pore size, and porosity can be adjusted by changing the protein concentrations during the fabrication process. The keratin scaffolds supported human adipose stem cells (hASCs) adhesion, proliferation, and differentiation. In vivo study performed on ICR mice showed that keratin scaffolds with hASCs shortened skin wound healing time, accelerated epithelialization, and promoted wound remodeling. Therefore, keratin scaffolds alone or together with hASCs may serve as therapeutic agents for repairing wounded tissue.

High-fat and high-glucose microenvironment decreases Runx2 and TAZ expression and inhibits bone regeneration in the mouse

BACKGROUND

Type 2 diabetes mellitus (T2DM) and hyperlipidemia are negatively related to bone regeneration. The aim of this study was to evaluate the effect of high-fat and high-glucose microenvironment on bone regeneration and to detect the expression of runt-related transcription factor 2 (Runx2) and transcriptional co-activator with PDZ-binding domain (TAZ) during this process.

METHODS

After establishing a high-fat and high-glucose mouse model, a 1 mm × 1.5 mm bone defect was developed in the mandible. On days 7, 14, and 28 after operation, bone regeneration was evaluated by hematoxylin-eosin staining, Masson staining, TRAP staining, and immunohistochemistry, while Runx2 and TAZ expression were detected by immunohistochemistry, RT-PCR, and Western blot analysis.

RESULTS

Our results showed that the inhibition of bone regeneration in high-fat and high-glucose group was the highest among the four groups. In addition, the expression of Runx2 in high-fat, high-glucose, and high-fat and high-glucose groups was weaker than that in the control group, but the expression of TAZ only showed a decreasing trend in the high-fat and high-glucose group during bone regeneration.

CONCLUSIONS

In conclusion, these results suggest that high-fat and high-glucose microenvironment inhibits bone regeneration, which may be related to the inhibition of Runx2 and TAZ expression.

Diabetes pharmacotherapy and effects on the musculoskeletal system

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

Platelet‑rich fibrin exudate promotes the proliferation and osteogenic differentiation of human periodontal ligament cells in vitro

The purpose of the present study was to evaluate the effects of platelet-rich fibrin (PRF) exudate on the proliferation, osteogenic differentiation and mineralization of human periodontal ligament cells (hPDLCs) in vitro. In the present study PRF was obtained with permission, from the peripheral blood of healthy donors and PRF exudates were collected on the 7th day of incubation. hPDLCs were obtained from healthy premolars, cultured by a tissue explant method and identified with anti-vimentin and anti-cytokeratin antibodies. PRF exudates were added to hPDLCs in different concentrations to evaluate cell proliferation and osteogenic differentiation. The proliferation of hPDLCs was measured using a colorimetric assay. Osteogenic differentiation and mineralization were determined by Alizarin red staining, alkaline phosphatase activity (ALP), western blotting and reverse transcription-quantitative polymerase chain reaction. Cell proliferation was enhanced by addition of the PRF exudate, which also promoted the formation of mineralized matrix nodules and upregulated ALP activity and osteoblast-associated levels of osteocalcin, runt-related transcription factor and osterix gene expression. As these stimulatory effects occurred in a dose-dependent manner, it was concluded that high concentrations of the PRF exudate served an essential role in the proliferation, osteogenic differentiation and mineralization of hPDLCs in vitro. The present study demonstrated that PRF exudate enhanced hPDLC proliferation, induced the osteoblastic differentiation of hPDLCs into mineralized tissue-formation cells in vitro, and may therefore provide potential benefits for periodontal tissue engineering; contributing to the primary processes of periodontal tissue regeneration. From the perspective of both economics and biology, PRF has greater clinical benefits than analogous growth factors.

HAMSCs/HBMSCs coculture system ameliorates osteogenesis and angiogenesis against glucolipotoxicity

Osteoporosis and vascular lesions induced by glucolipotoxicity are common complications of diabetes mellitus (DM). In order to deal with these complications, we designed a new therapeutic strategy, i.e. coculture system containing human amnion-derived mesenchymal stem cells (HAMSCs) and human bone marrow mesenchymal stem cells (HBMSCs). Two in vitro coculture models, transwell and mixed cocultures, were proposed for 7 days with variable HAMSCs: HBMSCs ratios. Then, supernatant from each coculture was used to reverse the deficiency of HBMSCs and human umbilical vein endothelial cells (HUVECs) impaired by high glucose and palmitic acid (GP). We found that glucolipotoxicity caused by GP remarkably inhibited cell proliferation, osteogenic differentiation and superoxide dismutase (SOD) activity, as well as induced the reactive oxygen species (ROS) level in HBMSCs. Meanwhile, glucolipotoxicity suppressed cell proliferation, tube formation capacity and angiogenic potential of HUVECs. Though, HAMSCs/HBMSCs coculture system reduced HBMSCs dysfunction by antioxidant properties and promoted angiogenesis in HUVECs. The mixed HAMSCs/HBMSCs coculture at the optimal ratio of 3/1 showed significantly greater cell proliferation, antioxidant properties, osteogenic and angiogenic differentiation than HBMSCs or HUVECs alone. In conclusion, the current coculture system of HAMSCs/HBMSCs can be a potential therapeutic material for advancing bone and vascular regeneration against DM-induced glucolipotoxicity.

Enhanced Bone Regeneration by Diabetic Cell-Based Adenoviral BMP-2 Gene Therapy in Diabetic Animals

The application of bone morphogenetic protein 2 (BMP-2) has been extensively investigated to improve diabetes-impaired bone healing; however, the delivery of BMP-2 by gene therapy for bone regeneration has rarely been investigated in diabetic animals. In this study, we aimed to evaluate which cells induce more new bone formation in diabetic animals when cell-based BMP2 gene therapy is applied. For this purpose, we harvested bone marrow stromal cells (BMSCs) twice in the same animal before (non-diabetic BMSCs; nBMSCs) and after diabetes induction (diabetic BMSCs; dBMSCs) using modified bone marrow ablation methods. And then, cells were transduced by adenoviral vectors carrying the BMP2 gene (AdBMP2). In in vitro, AdBMP2-transfected dBMSCs (B2/dBMSCs) produced higher BMP-2 mRNA levels over 48 h, whereas AdBMP2-transfected nBMSCs (B2/nBMSCs) exhibited a transient increase in BMP-2 mRNA followed by a decrease to the baseline level within 48 h. Both B2/dBMSCs and B2/nBMSCs induced secretion of BMP-2 for 3 weeks. However, B2/dBMSC BMP-2 secretion peaked from day 3 to 10, whereas B2/nBMSC BMP-2 secretion peaked from day 1 to 7. The analysis of osteogenic activity revealed that mineralization nodule formation and the expression levels of osteogenic genes were significantly higher in B2/dBMSCs than B2/nBMSCs and were accompanied by upregulation of canonical Wnt/β-catenin and Smad signaling. AdBMP2-transfected autologous cells were implanted into critical-sized calvarial defects in diabetic animals and induced significantly more bone regeneration than non-AdBMP2-transfected cells. In addition, B2/dBMSCs led to significantly more new bone formation than B2/nBMSCs. Thus, BMP2 gene therapy using diabetic cells effectively supported diabetic bone healing and it was related to the enhanced responses to AdBMP2 of dBMSCs.

Bioinformatic approaches to interrogating vitamin D receptor signaling

Bioinformatics applies unbiased approaches to develop statistically-robust insight into health and disease. At the global, or "20,000 foot" view bioinformatic analyses of vitamin D receptor (NR1I1/VDR) signaling can measure where the VDR gene or protein exerts a genome-wide significant impact on biology; VDR is significantly implicated in bone biology and immune systems, but not in cancer. With a more VDR-centric, or "2000 foot" view, bioinformatic approaches can interrogate events downstream of VDR activity. Integrative approaches can combine VDR ChIP-Seq in cell systems where significant volumes of publically available data are available. For example, VDR ChIP-Seq studies can be combined with genome-wide association studies to reveal significant associations to immune phenotypes. Similarly, VDR ChIP-Seq can be combined with data from Cancer Genome Atlas (TCGA) to infer the impact of VDR target genes in cancer progression. Therefore, bioinformatic approaches can reveal what aspects of VDR downstream networks are significantly related to disease or phenotype.

Estrogen Deficiency Exacerbates Type 1 Diabetes-Induced Bone TNF-α Expression and Osteoporosis in Female Mice

Estrogen deficiency after menopause is associated with rapid bone loss, osteoporosis, and increased fracture risk. Type 1 diabetes (T1D), characterized by hypoinsulinemia and hyperglycemia, is also associated with bone loss and increased fracture risk. With better treatment options, T1D patients are living longer; therefore, the number of patients having both T1D and estrogen deficiency is increasing. Little is known about the mechanistic impact of T1D in conjunction with estrogen deficiency on bone physiology and density. To investigate this, 11-week-old mice were ovariectomized (OVX), and T1D was induced by multiple low-dose streptozotocin injection. Microcomputed tomographic analysis indicated a marked reduction in trabecular bone volume fraction (BVF) in T1D-OVX mice (~82%) that was far greater than the reductions (~50%) in BVF in either the OVX and T1D groups. Osteoblast markers, number, and activity were significantly decreased in T1D-OVX mice, to a greater extent than either T1D or OVX mice. Correspondingly, marrow adiposity was significantly increased in T1D-OVX mouse bone. Bone expression analyses revealed that tumor necrosis factor (TNF)-α levels were highest in T1D-OVX mice and correlated with bone loss, and osteoblast and osteocyte death. In vitro studies indicate that estrogen deficiency and high glucose enhance TNF-α expression in response to inflammatory signals. Taken together, T1D combined with estrogen deficiency has a major effect on bone inflammation, which contributes to suppressed bone formation and osteoporosis. Understanding the mechanisms/effects of estrogen deficiency in the presence of T1D on bone health is essential for fracture prevention in this patient population.

Increased levels of Dickkopf-1 are indicative of Wnt/β-catenin downregulation and lower osteoblast signaling in children and adolescents with type 1 diabetes mellitus, contributing to lower bone mineral density

Higher levels of Dickkopf-1, which is an inhibitor of Wnt/β-catenin bone metabolic pathway, could be indicative of downregulated Wnt system, with possible lower osteoblast activation and higher osteoclast signaling in type 1 diabetes mellitus children and adolescents. Dickkopf-1 could significantly contribute to diabetes osteopathy.

INTRODUCTION

Increased fracture risk and elevated Dickkopf-1 levels, which is an inhibitor of Wnt/β-catenin bone metabolic pathway, have been documented in adult patients with type 2 diabetes mellitus (T2D), while no relevant data exist on childhood type 1 diabetes (T1D). Our aim was to study plasma Dickkopf-1 distribution in children and adolescents with T1D and to correlate Dickkopf-1 with metabolic bone markers and bone mineral density (BMD).

METHODS

We evaluated 40 children and adolescents with T1D (mean ± SD age 13.04 ± 3.53 years, T1D duration 5.15 ± 3.33 years) and 40 healthy age-matched and gender-matched controls (age 12.99 ± 3.3 years). Dickkopf-1 and bone metabolic markers were measured, while total body and lumbar spine BMD were evaluated with dual-energy X-ray absorptiometry (DXA).

RESULTS

Dickkopf-1 demonstrated a Gaussian distribution, with higher levels in T1D patients (13.56 ± 5.34 vs 11.35 ± 3.76 pmol/L, p = 0.024). Higher values were found in boys and in prepubertal children. Dickkopf-1 correlated positively with osteoprotegerin and fasting glucose in patients, while positive correlation with sclerostin and total soluble receptor activator of nuclear factor-kappaB ligand (s-RANKL) was found in controls. Positive correlations with C-telopeptide cross-links (CTX), osteocalcin, alkaline phosphatase, phosphate, and insulin-like growth factor 1 (IGF1) were documented in both groups. Lumbar spine Z-score was positively associated with Dickkopf-1 in controls, while a negative trend was found in patients.

CONCLUSIONS

Higher levels of Dickkopf-1 could indicate a downregulated Wnt/β-catenin system with possible lower osteoblast activation and higher osteoclast signaling in T1D children and adolescents. Dickkopf-1 could possibly be a significant contributor of T1D osteopathy. Future therapies could focus on Wnt/β-catenin metabolic pathway.

The impact of SGLT2 inhibitors, compared with insulin, on diabetic bone disease in a mouse model of type 1 diabetes

Skeletal co-morbidities in type 1 diabetes include an increased risk for fracture and delayed fracture healing, which are intertwined with disease duration and the presence of other diabetic complications. As such, chronic hyperglycemia is undoubtedly a major contributor to these outcomes, despite standard insulin-replacement therapy. Therefore, using the streptozotocin (STZ)-induced model of hypoinsulinemic hyperglycemia in DBA/2J male mice, we compared the effects of two glucose lowering therapies on the fracture resistance of bone and markers of bone turnover. Twelve week-old diabetic (DM) mice were treated for 9weeks with: 1) oral canagliflozin (CANA, dose range ~10-16mg/kg/day), an inhibitor of the renal sodium-dependent glucose co-transporter type 2 (SGLT2); 2) subcutaneous insulin, via minipump (INS, 0.125units/day); 3) co-therapy (CANA+INS); or 4) no treatment (STZ, without therapy). These groups were also compared to non-diabetic control groups. Untreated diabetic mice experienced increased bone resorption and significant deficits in cortical and trabecular bone that contributed to structural weakness of the femur mid-shaft and the lumbar vertebra, as determined by three-point bending and compression tests, respectively. Treatment with either canagliflozin or insulin alone only partially rectified hyperglycemia and the diabetic bone phenotype. However, when used in combination, normalization of glycemic control was achieved, and a prevention of the DM-related deterioration in bone microarchitecture and bone strength occurred, due to additive effects of canagliflozin and insulin. Nevertheless, CANA-treated mice, whether diabetic or non-diabetic, demonstrated an increase in urinary calcium loss; FGF23 was also increased in CANA-treated DM mice. These findings could herald ongoing bone mineral losses following CANA exposure, suggesting that certain CANA-induced skeletal consequences might detract from therapeutic improvements in glycemic control, as they relate to diabetic bone disease.

Diabetes and Bone Marrow Adiposity

PURPOSE OF REVIEW

This study aims to describe bone marrow fat changes in diabetes and to discuss the potential role of marrow fat in skeletal fragility.

RECENT FINDINGS

Advances in non-invasive imaging have facilitated marrow fat research in humans. In contrast to animal studies which clearly demonstrate higher levels of marrow fat in diabetes, human studies have shown smaller and less certain differences. Marrow fat has been reported to correlate with A1c, and there may be a distinct marrow lipid saturation profile in diabetes. Greater marrow fat is associated with impaired skeletal health. Marrow fat may be a mediator of skeletal fragility in diabetes. Circulating lipids, growth hormone alterations, visceral adiposity, and hypoleptinemia have been associated with greater marrow fat and may represent potential mechanisms for the putative effects of diabetes on marrow fat, although other factors likely contribute. Additional research is needed to further define the role of marrow fat in diabetic skeletal fragility and to determine whether marrow fat is a therapeutic target.

Effects of Type 1 Diabetes on Osteoblasts, Osteocytes, and Osteoclasts

PURPOSE OF REVIEW

To describe the effects of type 1 diabetes on bone cells.

RECENT FINDINGS

Type 1 diabetes (T1D) is associated with low bone mineral density, increased risk of fractures, and poor fracture healing. Its effects on the skeleton were primarily attributed to impaired bone formation, but recent data suggests that bone remodeling and resorption are also compromised. The hyperglycemic and inflammatory environment associated with T1D impacts osteoblasts, osteocytes, and osteoclasts. The mechanisms involved are complex; insulinopenia, pro-inflammatory cytokine production, and alterations in gene expression are a few of the contributing factors leading to poor osteoblast activity and survival and, therefore, poor bone formation. In addition, the observed sclerostin level increase accompanied by decreased osteocyte number and enhanced osteoclast activity in T1D results in uncoupling of bone remodeling. T1D negatively impacts osteoblasts and osteocytes, whereas its effects on osteoclasts are not well characterized, although the limited studies available indicate increased osteoclast activity, favoring bone resorption.

Nutlin-3 treatment spares cisplatin-induced inhibition of bone healing while maintaining osteosarcoma toxicity

The majority of Osteosarcoma (OS) patients are treated with a combination of chemotherapy, resection, and limb salvage protocols. These protocols include distraction osteogenesis (DO), which is characterized by direct new bone formation. Cisplatin (CDP) is extensively used for OS chemotherapy and recent studies, using a mouse DO model, have demonstrated that CDP has profound negative effects on bone repair. Recent oncological therapeutic strategies are based on the use of standard cytotoxic drugs plus an assortment of biologic agents. Here we demonstrate that the previously reported CDP-associated inhibition of bone repair can be modulated by the administration of a small molecule p53 inducer (nutlin-3). The effects of nutlin-3 on CDP osteotoxicity were studied using both pre- and post-operative treatment models. In both cases the addition of nutlin-3, bracketing CDP exposure, demonstrated robust and significant bone sparing activity (p < 0.01-0.001). In addition the combination of nutlin-3 and CDP induced equivalent OS tumor killing in a xenograft model. Collectively, these results demonstrate that the induction of p53 peri-operatively protects bone healing from the toxic effects of CDP, while maintaining OS toxicity. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1716-1724, 2016.

Local Application of Isogenic Adipose-Derived Stem Cells Restores Bone Healing Capacity in a Type 2 Diabetes Model

Bone regeneration is typically a reliable process without scar formation. The endocrine disease type 2 diabetes prolongs and impairs this healing process. In a previous work, we showed that angiogenesis and osteogenesis-essential steps of bone regeneration-are deteriorated, accompanied by reduced proliferation in type 2 diabetic bone regeneration. The aim of the study was to improve these mechanisms by local application of adipose-derived stem cells (ASCs) and facilitate bone regeneration in impaired diabetic bone regeneration. The availability of ASCs in great numbers and the relative ease of harvest offers unique advantages over other mesenchymal stem cell entities. A previously described unicortical tibial defect model was utilized in diabetic mice (Lepr(db-/-)). Isogenic mouse adipose-derived stem cells (mASCs)(db-/db-) were harvested, transfected with a green fluorescent protein vector, and isografted into tibial defects (150,000 living cells per defect). Alternatively, control groups were treated with Dulbecco's modified Eagle's medium or mASCs(WT). In addition, wild-type mice were identically treated. By means of immunohistochemistry, proteins specific for angiogenesis, cell proliferation, cell differentiation, and bone formation were analyzed at early (3 days) and late (7 days) stages of bone regeneration. Additionally, histomorphometry was performed to examine bone formation rate and remodeling. Histomorphometry revealed significantly increased bone formation in mASC(db-/db-)-treated diabetic mice as compared with the respective control groups. Furthermore, locally applied mASCs(db-/db-) significantly enhanced neovascularization and osteogenic differentiation. Moreover, bone remodeling was upregulated in stem cell treatment groups. Local application of mACSs can restore impaired diabetic bone regeneration and may represent a therapeutic option for the future.

SIGNIFICANCE

This study showed that stem cells obtained from fat pads of type 2 diabetic mice are capable of reconstituting impaired bone regeneration in type 2 diabetes. These multipotent stem cells promote both angiogenesis and osteogenesis in type 2 diabetic bony defects. These data might prove to have great clinical implications for bony defects in the ever-increasing type 2 diabetic patient population.

The influence of anisotropic nano- to micro-topography on in vitro and in vivo osteogenesis

AIM

Topographically modified substrates are increasingly used in tissue engineering to enhance biomimicry. The overarching hypothesis is that topographical cues will control cellular response at the cell-substrate interface.

MATERIALS & METHODS

The influence of anisotropically ordered poly(lactic-co-glycolic acid) substrates (constant groove width of ~1860 nm; constant line width of ~2220 nm; variable groove depth of ~35, 306 and 2046 nm) on in vitro and in vivo osteogenesis were assessed.

RESULTS & DISCUSSION

We demonstrate that substrates with groove depths of approximately 306 and 2046 nm promote osteoblast alignment parallel to underlined topography in vitro. However, none of the topographies assessed promoted directional osteogenesis in vivo.

CONCLUSION

2D imprinting technologies are useful tools for in vitro cell phenotype maintenance.

MECHANISMS IN ENDOCRINOLOGY: Mechanisms and evaluation of bone fragility in type 1 diabetes mellitus

Subjects with type 1 diabetes mellitus (T1DM) have decreased bone mineral density and an up to sixfold increase in fracture risk. Yet bone fragility is not commonly regarded as another unique complication of diabetes. Both animals with experimentally induced insulin deficiency syndromes and patients with T1DM have impaired osteoblastic bone formation, with or without increased bone resorption. Insulin/IGF1 deficiency appears to be a major pathogenetic mechanism involved, along with glucose toxicity, marrow adiposity, inflammation, adipokine and other metabolic alterations that may all play a role on altering bone turnover. In turn, increasing physical activity in children with diabetes as well as good glycaemic control appears to provide some improvement of bone parameters, although robust clinical studies are still lacking. In this context, the role of osteoporosis drugs remains unknown.

Scaffold-Free Fabrication of Osteoinductive Cellular Constructs Using Mouse Gingiva-Derived Induced Pluripotent Stem Cells

Three-dimensional (3D) cell constructs are expected to provide osteoinductive materials to develop cell-based therapies for bone regeneration. The proliferation and spontaneous aggregation capability of induced pluripotent stem cells (iPSCs) thus prompted us to fabricate a scaffold-free iPSC construct as a transplantation vehicle. Embryoid bodies of mouse gingival fibroblast-derived iPSCs (GF-iPSCs) were seeded in a cell chamber with a round-bottom well made of a thermoresponsive hydrogel. Collected ball-like cell constructs were cultured in osteogenic induction medium for 30 days with gentle shaking, resulting in significant upregulation of osteogenic marker genes. The constructs consisted of an inner region of unstructured cell mass and an outer osseous tissue region that was surrounded by osteoblast progenitor-like cells. The outer osseous tissue was robustly calcified with elemental calcium and phosphorous as well as hydroxyapatite. Subcutaneous transplantation of the GF-iPSC constructs into immunodeficient mice contributed to extensive ectopic bone formation surrounded by teratoma tissue. These results suggest that mouse GF-iPSCs could facilitate the fabrication of osteoinductive scaffold-free 3D cell constructs, in which the calcified regions and surrounding osteoblasts may function as scaffolds and drivers of osteoinduction, respectively. With incorporation of technologies to inhibit teratoma formation, this system could provide a promising strategy for bone regenerative therapies.

Effects of diabetes on tooth movement and root resorption after orthodontic force application in rats

OBJECTIVE

To investigate the effects of diabetes on orthodontic tooth movement and orthodontically induced root resorption in rats.

SETTING AND SAMPLE POPULATION

Twenty-three 10-week-old male Sprague-Dawley rats divided into control (n = 7), diabetes (n = 9), and diabetes + insulin (n = 7) groups.

MATERIALS AND METHODS

Diabetes was induced by administering a single intraperitoneal injection of streptozotocin. Rats with a blood glucose level exceeding 250 mg/dl were assigned to the diabetes group. Insulin was administered daily to the diabetes + insulin group. A nickel-titanium closed-coil spring of 10 g was applied for 2 weeks to the maxillary left first molar in all rats to induce mesial tooth movement. Tooth movement was measured using microcomputed tomography images. To determine the quantity of root resorption, the mesial surfaces of the mesial and distal roots of the first molar were analyzed using both scanning electron microscopy and scanning laser microscopy.

RESULTS

After 2 weeks, the amount of tooth movement in the diabetic rats was lower than that in the control rats. Root resorption was also significantly lower in the diabetic rats. These responses of the rats caused by diabetes were mostly diminished by insulin administration.

CONCLUSIONS

Diabetes significantly reduced orthodontic tooth movement and orthodontically induced root resorption in rats. The regulation of blood glucose level through insulin administration largely reduced these abnormal responses to orthodontic force application.

SGLT2 inhibitor therapy improves blood glucose but does not prevent diabetic bone disease in diabetic DBA/2J male mice

Persons with type 1 and type 2 diabetes have increased fracture risk, attributed to deficits in the microarchitecture and strength of diabetic bone, thought to be mediated, in part, by the consequences of chronic hyperglycemia. Therefore, to examine the effects of a glucose-lowering SGLT2 inhibitor on blood glucose (BG) and bone homeostasis in a model of diabetic bone disease, male DBA/2J mice with or without streptozotocin (STZ)-induced hyperglycemia were fed chow containing the SGLT2 inhibitor, canagliflozin (CANA), or chow without drug, for 10weeks of therapy. Thereafter, serum bone biomarkers were measured, fracture resistance of cortical bone was assessed by μCT analysis and a three-point bending test of the femur, and vertebral bone strength was determined by compression testing. In the femur metaphysis and L6 vertebra, long-term diabetes (DM) induced deficits in trabecular bone microarchitecture. In the femur diaphysis, a decrease in cortical bone area, cortical thickness and minimal moment of inertia occurred in DM (p<0.0001, for all) while cortical porosity was increased (p<0.0001). These DM changes were associated with reduced fracture resistance (decreased material strength and toughness; decreased structural strength and rigidity; p<0.001 for all). Significant increases in PTH (p<0.0001), RatLAPs (p=0.0002), and urine calcium concentration (p<0.0001) were also seen in DM. Canagliflozin treatment improved BG in DM mice by ~35%, but did not improve microarchitectural parameters. Instead, in canagliflozin-treated diabetic mice, a further increase in RatLAPs was evident, possibly suggesting a drug-related intensification of bone resorption. Additionally, detrimental metaphyseal changes were noted in canagliflozin-treated control mice. Hence, diabetic bone disease was not favorably affected by canagliflozin treatment, perhaps due to insufficient glycemic improvement. Instead, in control mice, long-term exposure to SGLT2 inhibition was associated with adverse effects on the trabecular compartment of bone.

Transient Intermittent Hypoxia Exposure Disrupts Neonatal Bone Strength

A brief intermittent hypoxia (IH, ambient O2 levels alternating between room air and 12% O2) for 1 h immediately after birth resulted in pancreatic islet dysfunction associated with zinc deficiency as previously reported. We hypothesized that IH exposure modulates zinc homeostasis in bone as well, which leads to increased bone fragility. To test this hypothesis, we used neonatal rats and human osteoblasts (HObs). To examine IH influences on osteoblasts devoid of neural influences, we quantified amounts of alkaline phosphatase and mineralization in IH-treated HObs. Bones harvested from IH-treated animals showed significantly reduced hardness and elasticity. The IH group also showed discretely decreased levels of alkaline phosphatase and mineralization amounts. The IH group showed a decreased expression of ZIP8 or Zrt and Irt-like protein 8 (a zinc uptake transporter), Runx2 (or Runt-related transcription factor 2, a master protein in bone formation), Collagen-1 (a major protein comprising the extracellular matrix of the bone), osteocalcin, and zinc content. When zinc was eliminated from the media containing HObs using a zinc chelate and added later with zinc sulfate, Runx2, ZIP8, and osteocalcin expression decreased first, and recovered with zinc supplementation. Adenovirus-mediated ZIP8 over-expression in osteoblasts increased mineralization significantly as well. We conclude that IH impairs zinc homeostasis in bones and osteoblasts, and that such disturbances decrease bone strength, which can be recovered by zinc supplementation.

Diabetes mellitus affects the biomechanical function of the callus and the expression of TGF-beta1 and BMP2 in an early stage of fracture healing

Transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2) are important regulators of bone repair and regeneration. In this study, we examined whether TGF-β1 and BMP-2 expressions were delayed during bone healing in type 1 diabetes mellitus. Tibial fractures were created in 95 diabetic and 95 control adult male Wistar rats of 10 weeks of age. At 1, 2, 3, 4, and 5 weeks after fracture induction, five rats were sacrificed from each group. The expressions of TGF-β1 and BMP2 in the fractured tibias were measured by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction, weekly for the first 5 weeks post-fracture. Mechanical parameters (bending rigidity, torsional rigidity, destruction torque) of the healing bones were also assessed at 3, 4, and 5 weeks post-fracture, after the rats were sacrificed. The bending rigidity, torsional rigidity and destruction torque of the two groups increased continuously during the healing process. The diabetes group had lower mean values for bending rigidity, torsional rigidity and destruction torque compared with the control group (P<0.05). TGF-β1 and BMP-2 expression were significantly lower (P<0.05) in the control group than in the diabetes group at postoperative weeks 1, 2, and 3. Peak levels of TGF-β1 and BMP-2 expression were delayed by 1 week in the diabetes group compared with the control group. Our results demonstrate that there was a delayed recovery in the biomechanical function of the fractured bones in diabetic rats. This delay may be associated with a delayed expression of the growth factors TGF-β1 and BMP-2.

Substrate topography: A valuable in vitro tool, but a clinical red herring for in vivo tenogenesis

Controlling the cell-substrate interactions at the bio-interface is becoming an inherent element in the design of implantable devices. Modulation of cellular adhesion in vitro, through topographical cues, is a well-documented process that offers control over subsequent cellular functions. However, it is still unclear whether surface topography can be translated into a clinically functional response in vivo at the tissue/device interface. Herein, we demonstrated that anisotropic substrates with a groove depth of ∼317nm and ∼1988nm promoted human tenocyte alignment parallel to the underlying topography in vitro. However, the rigid poly(lactic-co-glycolic acid) substrates used in this study upregulated the expression of chondrogenic and osteogenic genes, indicating possible tenocyte trans-differentiation. Of significant importance is that none of the topographies assessed (∼37nm, ∼317nm and ∼1988nm groove depth) induced extracellular matrix orientation parallel to the substrate orientation in a rat patellar tendon model. These data indicate that two-dimensional imprinting technologies are useful tools for in vitro cell phenotype maintenance, rather than for organised neotissue formation in vivo, should multifactorial approaches that consider both surface topography and substrate rigidity be established.

STATEMENT OF SIGNIFICANCE

Herein, we ventured to assess the influence of parallel groves, ranging from nano- to micro-level, on tenocytes response in vitro and on host response using a tendon and a subcutaneous model. In vitro analysis indicates that anisotropically ordered micro-scale grooves, as opposed to nano-scale grooves, maintain physiological cell morphology. The rather rigid PLGA substrates appeared to induce trans-differentiation towards chondrogenic and/or steogenic lineage, as evidence by TILDA gene analysis. In vivo data in both tendon and subcutaneous models indicate that none of the substrates induced bidirectional host cell and tissue growth. Collective, these observations indicate that two-dimensional imprinting technologies are useful tools for in vitro cell phenotype maintenance, rather than for directional neotissue formation, should multifactorial approaches that consider both surface topography and substrate rigidity be established.