Energy Excess, Glucose Utilization, and Skeletal Remodeling: New Insights

Abstract

Skeletal complications have recently been recognized as another of the several comorbidities associated with diabetes. Clinical studies suggest that disordered glucose and lipid metabolism have a profound effect on bone. Diabetes-related changes in skeletal homeostasis result in a significant increased risk of fractures, although the pathophysiology may differ from postmenopausal osteoporosis. Efforts to understand the underlying mechanisms of diabetic bone disease have focused on the direct interaction of adipose tissue with skeletal remodeling and the potential influence of glucose utilization and energy uptake on these processes. One aspect that has emerged recently is the major role of the central nervous system in whole-body metabolism, bone turnover, adipose tissue remodeling, and beta cell secretion of insulin. Importantly, the skeleton contributes to the metabolic balance inherent in physiologic states. New animal models have provided the insights necessary to begin to dissect the effects of obesity and insulin resistance on the acquisition and maintenance of bone mass. In this Perspective, we focus on potential mechanisms that underlie the complex interactions between adipose tissue and skeletal turnover by focusing on the clinical evidence and on preclinical studies indicating that glucose intolerance may have a significant impact on the skeleton. In addition, we raise fundamental questions that need to be addressed in future studies to resolve the conundrum associated with glucose intolerance, obesity, and osteoporosis. © 2015 American Society for Bone and Mineral Research. KEY WORDS: BONE-FAT INTERACTIONS; SYSTEMS BIOLOGY; BONE INTERACTORS; CELL/TISSUE SIGNALING; TRANSCRIPTION FACTORS; DISEASES AND DISORDERS OF/RELATED TO BONE Clinical Insight Into the Effect of Disordered Glucose and Lipids Homeostasis on BoneD iabetes mellitus (DM) can be considered a disease of intracellular glucose starvation in muscle and fat, due to either lack of insulin (Type 1 [T1D]) or impaired insulin action (Type 2 [T2D]). Both types of DM are associated with an increase in fractures; however, the skeletal phenotype is very different. T1D patients have reduced bone mineral density (BMD), due to insulin and amylin deficiency, whereas T2D patients have either normal or high BMD. T2D is a disease of disordered energy storage as well as glucose intolerance and altered bone strength. Its prevalence is high and not abating. In the United States, 29.1 million people-9.3% of the population-have diabetes; among them, nearly 60% are characterized as obese (http://www.cdc.gov). Insulin resistance is a characteristic feature of T2D in liver, muscle, and fat, leading to glucose intolerance, elevated cardiometabolic risk factors (eg, low-density lipoprotein [LDL] cholesterol), and excess hepatic glucose output. Visceral adipocytes, in particular, are large and surrounded by fibrous and inflammatory elements.In clinical medicine a major paradox is the relationship of obesity to the skeleton. Obese individuals tend to have higher...

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“…Type I Diabetes in particular is associated with a variety of bone complications including reduced bone mineral density, increased fracture risk and poor fracture healing in both humans and rodent models [57,58]. Historically, the effects of diabetes on the skeleton have been primarily attributed to deleterious effects on osteoblasts and bone formation, but more recent data suggests that bone resorption is also affected [59–64].…”

PPARG Post-translational Modifications Regulate Bone Formation and Bone Resorption

“…The lack of the association between higher BMD and lower incidence of fractures indicates that in T2D bone biomechanical properties are compromised. Indeed, diabetic bone, particularly in the appendicular skeleton, has a number of structural characteristics which predispose to fractures, including greater cortical porosity, smaller cortical area, decreased bone material strength, and high bone marrow adiposity (Lecka-Czernik and Rosen, 2015). …”

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