Defective bone formation is common in patients with diabetes, suggesting that insulin normally exerts anabolic actions in bone. However, because insulin can cross-activate the insulinlike growth factor type 1 receptor (IGF-1R), which also functions in bone, it has been difficult to establish the direct (IGF-1-independent) actions of insulin in osteoblasts. To overcome this problem, we examined insulin signaling and action in primary osteoblasts engineered for conditional disruption of the IGF-1 receptor (⌬IGF-1R). Calvarial osteoblasts from mice carrying floxed IGF-1R alleles were infected with adenoviral vectors expressing the Cre recombinase (Ad-Cre) or green fluorescent protein (Ad-GFP) as control. Disruption of IGF-1R mRNA (>90%) eliminated IGF-1R without affecting insulin receptor (IR) mRNA and protein expression and eliminated IGF-1R/IR hybrids. In ⌬IGF-1R osteoblasts, insulin signaling was markedly increased as evidenced by increased phosphorylation of insulin receptor substrate 1/2 and enhanced ERK/Akt activation. Microarray analysis of RNA samples from insulin-treated, ⌬IGF-1R osteoblasts revealed striking changes in several genes known to be downstream of ERK including Glut-1 and c-fos. Treatment of osteoblasts with insulin induced Glut-1 mRNA, increased 2-[1,2-3 H]-deoxy-D-glucose uptake, and enhanced proliferation. Moreover, insulin treatment rescued the defective differentiation and mineralization of ⌬IGF-1R osteoblasts, suggesting that IR signaling can compensate, at least in part, for loss of IGF-1R signaling. We conclude that insulin exerts direct anabolic actions in osteoblasts by activation of its cognate receptor and that the strength of insulin-generated signals is tempered through interactions with the IGF-1R.Insulin and insulin-like growth factor 1 (IGF-1) 2 are related signaling molecules that evolved from a common ancestor pathway originally involved in sensing and integrating signals arising from nutrient and growth factor availability. During evolution, this primitive receptor pathway diverged into two distinct hormonal systems that in mammals serve different but overlapping developmental and metabolic functions (1, 2). These receptors belong to the family of ligand-activated receptor kinases and are abundantly expressed in osteoblasts (3, 4). Unlike other receptor tyrosine kinases, these proteins exist at the cell surface as homodimers composed of two identical ␣/␤ (␣ 2 /␤ 2 ) monomers or as heterodimers (discussed below) composed of two different receptor monomers (e.g. IR ␣ ␤/IGF-1R ␣ ␤). Upon ligand binding, they undergo a conformational change that facilitates binding to ATP and autophosphorylation (5, 6). Autophosphorylation increases the kinase activity of IR-type receptors by 3 orders of magnitude, enabling them to phosphorylate a number of substrate proteins and engender growth or metabolic responses (7). IRS proteins act as mediators of insulin, IGF, and cytokine signaling in a variety of cell types. These adaptor molecules recruit and activate downstream signaling cascades su...

A prolonged depression of cardiovascular function occurs in males after trauma-hemorrhagic shock (T-H). Although a correlation between increased circulatory IL-6 levels and poor outcome has been reported after T-H, it remains unknown whether T-H increases IL-6 levels locally in cardiomyocytes and whether there is a correlation between altered cardiac function and local IL-6 production after T-H. T-H was induced in normal, castrated (2 wk before T-H), and 17β-estradiol (E2)-treated (0.5 mg sc, 1 wk before T-H) adult male rats. At 2 h after T-H or sham operation, cardiac output, heart rate, mean arterial pressure, positive and negative first derivative of pressure (±dP/d t), stroke volume, and total peripheral resistance were determined. Cardiomyocytes were isolated and divided into two parts: one was used for measurements of intracellular IL-6 levels using fluorescein-activated cell sorting, and the other was used to isolate RNA to determine IL-6 gene expression by quantitative real-time PCR. In addition, cardiac IL-6 protein levels were measured in freshly isolated hearts by Western blotting. Cardiac output, stroke volume, +dP/d t, −dP/d t, and total peripheral resistance were markedly altered after T-H. These parameters, except −dP/d t, improved significantly in the castrated group; however, all these parameters were restored in E2-treated males. Cardiomyocyte IL-6 mRNA expression and intracellular IL-6 production increased after T-H. Cardiac IL-6 protein levels increased after T-H in freshly isolated heart. Castration and E2 treatment attenuated cardiomyocyte intracellular IL-6 levels and cardiac IL-6 protein levels after T-H; however, only E2 treatment attenuated cardiomyocyte IL-6 gene expression. Thus there is an inverse correlation between cardiomyocyte IL-6 levels and cardiac function after T-H. The salutary effects of E2 on cardiac function after T-H may be due in part to decreased IL-6 synthesis in cardiomyocytes.

Hyperglycemia and insulin resistance often occur following injury and/or critical illness. While intensive insulin treatment reduces hyperglycemia, mortality and morbidity in certain patients, little is known regarding the pathophysiology of acute insulin resistance following injury and infection. Studies suggest that acute insulin resistance is complex and may differ in a tissue-specific manner, involving multiple causative factors and intracellular signaling pathways. Therefore, the advantages of intensive insulin therapy may not be uniform to all injuries or critical illnesses. Clearly, the increased incidence of hypoglycemic incidents following intensive insulin therapy indicates a need to understand the underlying molecular mechanisms of the acute development of insulin resistance, which will allow a more targeted approach to treating altered glucose metabolism of critically ill patients. Historical perspectives on the link between hyperglycemia and intensive insulin therapyClaude Bernard first described the development of hyperglycemia following hemorrhagic shock in 1877 [1], and it is now accepted that many acute illnesses or injuries result in hyperglycemia, glucose intolerance and insulin resistance [2][3][4][5][6][7][8]. This 'diabetes of injury', now more commonly referred to as 'critical illness diabetes', can occur in patients without a previous history of Type 2 diabetes. Patients in the intensive care unit (ICU) with multiple injuries, extensive burns, major surgical trauma, or infections often present with 'critical illness diabetes'. Many survive the initial injury, but then succumb to multiple organ failure [9]. Although extensive research efforts have focused on strategies to prevent or reverse multiple organ failure, few results are encouraging and the mechanisms remain unclear [10][11][12]. However, intensive insulin therapy may result in substantial improvements [1,13], suggesting that perturbations of glucose metabolism contributes to multiple organ failure, as well as to other problems that occur in injured and critically ill individuals [14][15][16]. It is well known that insulin can have anti-inflammatory actions, but how intensive insulin therapy can potentially decrease morbidity and mortality in the ICU is still poorly understood. This review focusees on the development of hyperglycemia and insulin resistance following injury or critical illness, the controversy over how to treat these patients in the ICU, and the varying mechanisms by which insulin resistance develops in different tissues. 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 pertai...

No abstract