Diabetic osteoporosis is increasingly recognized as a significant comorbidity of type 1 diabetes mellitus. In contrast, type 2 diabetes mellitus is more commonly associated with modest increases in bone mineral density for age. Despite this dichotomy, clinical, in vivo, and in vitro data uniformly support the concept that new bone formation as well as bone microarchitectural integrity are altered in the diabetic state, leading to an increased risk for fragility fracture and inadequate bone regeneration following injury. In this review, we examine the contribution that insulin, as a potential anabolic agent in bone, may make to the pathophysiology of diabetic bone disease. Specifically, we have assimilated human and animal data examining the effects of endogenous insulin production, exogenous insulin administration, insulin sensitivity, and insulin signaling on bone. In so doing, we present evidence that insulin, acting as an anabolic agent in bone, can preserve and increase bone density and bone strength, presumably through direct and/or indirect effects on bone formation.

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The effects of type 1 diabetes on de novo bone formation during tibial distraction osteogenesis (DO) and on intact trabecular and cortical bone were studied using nonobese diabetic (NOD) mice and comparably aged nondiabetic NOD mice. Diabetic mice received treatment with insulin, vehicle, or no treatment during a 14-day DO procedure. Distracted tibiae were analyzed radiographically, histologically, and by microcomputed tomography (CT). Contralateral tibiae were analyzed using CT. Serum levels of insulin, osteocalcin, and cross-linked C-telopeptide of type I collagen were measured. Total new bone in the DO gap was reduced histologically (P < 0.001) and radiographically (P < 0.05) in diabetic mice compared with nondiabetic mice but preserved by insulin treatment. Serum osteocalcin concentrations were also reduced in diabetic mice (P < 0.001) and normalized with insulin treatment. Evaluation of the contralateral tibiae by CT and mechanical testing demonstrated reductions in trabecular bone volume and thickness, cortical thickness, cortical strength, and an increase in endosteal perimeter in diabetic animals, which were prevented by insulin treatment. These studies demonstrate that bone formation during DO is impaired in a model of type 1 diabetes and preserved by systemic insulin administration. Diabetes 54:2875-2881, 2005 T ype 1 diabetes is associated with several disorders of skeletal health, including decreased bone density, an increased risk for osteoporosis (1-6), and fragility fracture (7-9), as well as poor bone healing and regeneration characteristics (10), conditions which all rely, in part, upon an intramembranous component to bone formation. Increasing evidence suggests that skeletal abnormalities in type 1 diabetes may, in part, result from the detrimental effects of type 1 diabetes on bone formation. For example, decreased expression of transcription factors that regulate osteoblast differentiation have been demonstrated in animal models of type 1 diabetes (11). Numerous reports of bone histology in diabetic animals demonstrate decreased osteoblast number, osteoid volume, and mineral apposition rates (rev. in 12). In diabetic rats, plasma osteocalcin concentrations, a marker of osteoblast activity, acutely decline beginning on the 1st day of glucosuria (13). Similarly, serum concentrations of osteocalcin in children with newly diagnosed type 1 diabetes are significantly lower at the onset of disease (14). Serum markers correlated with bone formation (IGF-I, alkaline phosphatase, and osteocalcin) also are significantly lower in diabetic patients with osteopenia compared with those without osteopenia (2), and studies have demonstrated that lower bone mineral density (BMD) in type 1 diabetes is correlated with decreased markers of bone formation and more exaggerated dysregulation of the IGF system (15).The present study was designed to test the hypothesis that type 1 diabetes specifically impedes intramembranous bone formation by using a model of tibial distraction osteogenesis uniquely modified for use ...

Matrix metalloproteinases (MMPs), a family of proteinases including collagenases, gelatinases, stromely-sins, matrilysins, and membrane-type MMPs, affect the breakdown and turnover of extracellular matrix (ECM).Moreover, they are major physiologic determinants of ECM degradation and turnover in the glomerulus. Renal hypertrophy and abnormal ECM deposition are hallmarks of diabetic nephropathy (DN), suggesting that altered MMP expression or activation contributes to renal injury in DN. Herein, we review and summarize recent information supporting a role for MMPs in the pathogenesis of DN. Specifically, studies describing dysregulated activity of MMPs and/or their tissue inhibitors in various experimental models of diabetes, including animal models of type 1 or type 2 diabetes, clinical investigations of human type 1 or type 2 diabetes, and kidney cell culture studies are reviewed. KeywordsGelatinase; Podocyte; Extracellular matrix; Proteinases; Proteinuria Diabetic nephropathy-general overviewDiabetic nephropathy is stated to be the most common cause of end-stage renal disease in the United States [1]. Between 20% and 30% of patients with type 1 diabetes mellitus (DM) or type 2 DM will develop nephropathy [1], and among patients with type 1 DM, diabetic nephropathy develops in 40-50% of patients with a 20-year history of disease [2]. Among those individuals who develop renal dysfunction, several risk factors for the development of renal disease have been identified, including duration of diabetes, age at diagnosis, race, systemic or glomerular hypertension, poor glycemic control, genetic predisposition to kidney disease, and dietary composition [1][2][3]. However, the precise pathogenic mechanisms involved in the initiation and progression of diabetic nephropathy remain incompletely understood.The development of diabetic nephropathy has been described as a five-stage process, progressing from glomerular hyperfiltration and nephromegaly (Stage 1), to glomerular basement membrane thickening and mesangial expansion (Stage 2), to microalbuminuria and eventual decline in glomerular filtration rate (Stage 3), to frank proteinuria with severe hypertension and sequelae of moderate to severe renal insufficiency (Stage 4), to eventual endstage renal disease (Stage 5) [4,5]. It has been hypothesized that the early changes in glomerular basement membrane thickness and content ultimately affect filtration properties of the © Humana Press Inc. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript glomerular basement membrane, leading first to increased urinary albumin excretion and eventually to proteinuria. Similar histological findings are also seen in many rodent models of diabetic nephropathy. Because enlargement of the kidney mesangium due to extracellular matrix over-accumulation is a major characteristic of diabetic nephropathy, and because MMPs produced by the mesangial cell account for up to 70% of extracellular matrix degradation and turnover in the kidney during normal matrix remodeling,...

These findings suggest that, theoretically, exaggerated urinary loss of VDBP in T1D, particularly in persons with albuminuria, could contribute mechanistically to vitamin D deficiency in this disease.

OBJECTIVE -Dysregulation of matrix metalloproteinase (MMP)-2 may contribute pathologically to the development of diabetes complications, including diabetic retinopathy and coronary and peripheral arterial disease. Our objective was to explore whether systemic MMP-2 dysregulation could be demonstrated in type 1 diabetes and to determine how MMP-2 concentration relates to disease status.RESEARCH DESIGN AND METHODS -In this cross-sectional study, MMP-2 concentrations and MMP-2 activity were measured in plasma and timed urine samples from 93 type 1 diabetic and 50 healthy control subjects, aged 14 -40 years. Relationships between MMP-2 concentrations in these biological fluids and subject characteristics (sex, age, and duration of type 1 diabetes), indexes of glycemic control (A1C, fasting plasma glucose, and continuous glucose monitoring system average daily glucose), and measurements of renal function (urinary albumin excretion and glomerular filtration rate) were examined.RESULTS -Urine and plasma MMP-2 concentrations and plasma MMP-2 activity were all significantly elevated in type 1 diabetic subjects compared with those in control subjects. Urine MMP-2 concentrations, in particular, were correlated with several clinical parameters that infer increased risk for diabetic comorbidity and specifically for diabetic nephropathy, including higher A1C, longer duration of disease, evidence of renal hyperfiltration, and the presence of microalbuminuria.CONCLUSIONS -Urine and plasma MMP-2 concentrations are dysregulated in type 1 diabetes; urinary excretion of MMP-2, in particular, might provide a unique biomarker of diabetes-induced intrarenal pathologic processes. Diabetes Care 30:2321-2326, 2007M atrix metalloproteinases (MMPs) constitute a group of enzymes that hydrolyze protein components of the extracellular matrix (1). The subgroup of MMPs known as gelatinases, specifically gelatinase A (MMP-2) and gelatinase B (MMP-9) digest collagen, denatured collagens (i.e., gelatins), laminin, elastin, and fibronectin, among other substrates (2), and have been implicated in the pathological processes that contribute to fibrotic diseases, tumor progression, and inflammation (1,3,4).Dysregulation of gelatinase activity has also been implicated in the pathophysiology of diabetes complications. Specifically, gelatinase concentrations are increased in the systemic circulation ) and in the vitreous (MMP-2 [6] and MMP-9 [7]) of type 1 diabetic patients with diabetic retinopathy. Elevated retinal levels of MMP-2 and MMP-9 have also been demonstrated in an animal model of diabetic retinopathy (8). Increased circulating concentrations of MMP-2 have been observed in pediatric patients with type 1 diabetes who developed microangiopathy over a 5-year interval (9). Systemic concentrations of MMP-2 and MMP-9, in addition to gelatinase activity levels, are also increased in patients with type 2 diabetes and peripheral arterial disease (10).Data suggesting a link between MMP-2 dysregulation and diabetic nephropathy also exist but appear contra...

Type 1 diabetes (T1DM) increases the likelihood of a fracture. Despite serious complications in the healing of fractures among those with diabetes, the underlying causes are not delineated for the effect of diabetes on the fracture resistance of bone. Therefore, in a mouse model of T1DM, we have investigated the possibility that a prolonged state of diabetes perturbs the relationship between bone strength and structure (i.e., affects tissue properties). At 10, 15, and 18 weeks following injection of streptozotocin to induce diabetes, diabetic male mice and age-matched controls were examined for measures of skeletal integrity. We assessed 1) the moment of inertia (I MIN ) of the cortical bone within diaphysis, trabecular bone architecture of the metaphysis, and mineralization density of the tissue (TMD) for each compartment of the femur by microcomputed tomography and 2) biomechanical properties by three point bending test (femur) and nanoindentation (tibia). In the metaphysis, a significant decrease in trabecular bone volume fraction and trabecular TMD was apparent after 10 weeks of diabetes. For cortical bone, type 1 diabetes was associated with decreased cortical TMD, I MIN , rigidity, and peak moment as well as a lack of normal age-related increases in the biomechanical properties. However, there were only modest differences in material properties between diabetic and normal mice at both whole bone and tissue-levels. As the duration of diabetes increased, bone toughness decreased relative to control. If the sole effect of diabetes on bone strength was due to a reduction in bone size, then I MIN would be the only significant variable explaining the variance in the maximum moment. However, general linear modeling found that the relationship between peak moment and I MIN depended on whether the bone was from a diabetic mouse and the duration of diabetes. Thus, these Correspondence: Jeffry S. Nyman, Vanderbilt Orthopaedic Institute, Medical Center East, South Tower, Suite 4200, Nashville, TN 37232, jeffry.s.nyman@vanderbilt.edu, (615) 936-6296. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptBone. Author manuscript; available in PMC 2012 April 1.

Type 1 diabetes mellitus is associated with a number of disorders of skeletal health, conditions that rely, in part, on dynamic bone formation. A mouse model of distraction osteogenesis was used to study the consequences of streptozotocin-induced diabetes and insulin treatment on bone formation and osteoblastogenesis. In diabetic mice compared with control mice, new bone formation was decreased, and adipogenesis was increased in and around, respectively, the distraction gaps. Although insulin treatment restored bone formation to levels observed in nondiabetic control mice, it failed to significantly decrease adipogenesis. Molecular events altered during de novo bone formation in untreated type 1 diabetes mellitus, yet restored with insulin treatment were examined so as to clarify specific osteogenic genes that may contribute to diabetic bone disease. RNA from distraction gaps was analyzed by gene microarray and quantitative RT-PCR for osteogenic genes of interest. Runt-related transcription factor 2 (RUNX2), and several RUNX2 target genes, including matrix metalloproteinase-9, Akp2, integrin binding sialoprotein, Dmp1, Col1a2, Phex, Vdr, osteocalcin, and osterix, were all significantly down-regulated in the insulin-deficient, hyperglycemic diabetic animals; however, insulin treatment of diabetic animals significantly restored their expression. Expression of bone morphogenic protein-2, transcriptional coactivator with PDZ-binding motif, and TWIST2, all important regulators of RUNX2, were not impacted by the diabetic condition, suggesting that the defect in osteogenesis resides at the level of RUNX2 expression and its activity. Together, these data demonstrate that insulin and/or glycemic status can regulate osteogenesis in vivo, and systemic insulin therapy can, in large part, rescue the diabetic bone phenotype at the tissue and molecular level.