Molecular analysis of insulin receptor gene in Werner's syndrome

Changes in Cells Associated with Insulin Resistance

Insulin is a polypeptide hormone synthesized and secreted by pancreatic β-cells. It plays an important role as a metabolic hormone. Insulin influences the metabolism of glucose, regulating plasma glucose levels and stimulating glucose storage in organs such as the liver, muscles and adipose tissue. It is involved in fat metabolism, increasing the storage of triglycerides and decreasing lipolysis. Ketone body metabolism also depends on insulin action, as insulin reduces ketone body concentrations and influences protein metabolism. It increases nitrogen retention, facilitates the transport of amino acids into cells and increases the synthesis of proteins. Insulin also inhibits protein breakdown and is involved in cellular growth and proliferation. On the other hand, defects in the intracellular signaling pathways of insulin may cause several disturbances in human metabolism, resulting in several chronic diseases. Insulin resistance, also known as impaired insulin sensitivity, is due to the decreased reaction of insulin signaling for glucose levels, seen when glucose use in response to an adequate concentration of insulin is impaired. Insulin resistance may cause, for example, increased plasma insulin levels. That state, called hyperinsulinemia, impairs metabolic processes and is observed in patients with type 2 diabetes mellitus and obesity. Hyperinsulinemia may increase the risk of initiation, progression and metastasis of several cancers and may cause poor cancer outcomes. Insulin resistance is a health problem worldwide; therefore, mechanisms of insulin resistance, causes and types of insulin resistance and strategies against insulin resistance are described in this review. Attention is also paid to factors that are associated with the development of insulin resistance, the main and characteristic symptoms of particular syndromes, plus other aspects of severe insulin resistance. This review mainly focuses on the description and analysis of changes in cells due to insulin resistance.

Clinical approach to the patient with diabetes mellitus and very high insulin requirements

A number of patients with diabetes require very high (> 2 Ukg⁻¹ day⁻¹), or extremely high (> 3 Ukg⁻¹ day⁻¹), insulin doses for the management of their hyperglycemia. Unfortunately, many of the physicians who treat these patients limit themselves to prescribing ever higher doses of insulin, without questioning why. Furthermore, when the insulin requirements get to be extreme, demanding an explanation, clinicians are frequently lost in a sea of literature where there is not a single paper dealing with this problem systematically. A systematic approach to the evaluation of these patients is necessary to facilitate an appropriate diagnosis, select the most reasonable therapy, and hopefully improve the long-term outcome of these patients. This manuscript intends to provide the clinician with a review of the literature pertinent for the differential diagnosis, work-up, and management of these patients. We will review the definitions of insulin sensitivity during normality, the various degrees or categories of insulin resistance, and the expected insulin requirements during each of these states. Subsequently, we propose a simple alphabetic mnemonic approach to help remember the differential diagnosis, and a clinical algorithm to help guide the work-up of these patients. Lastly, we briefly discuss general management considerations in these conditions.

Hyperinsulinemia and insulin resistance in Wrn null mice fed a diabetogenic diet

Werner syndrome (WS) is an autosomal recessive progeroid syndrome caused by mutations in the Werner (Wrn) gene. WS patients have increased incidence of a number of chronic conditions including insulin resistance and type 2 diabetes. Since ingestion of foods that are high in fat and sugar is associated with increased incidence of diabetes, we examined if Wrn mutations might affect metabolic response to a diabetogenic diet. Four-month-old mice with a null mutation for the Wrn gene were fed a diet consisting of 36% fat (lard), 33% table sugar, and 20% protein plus balanced vitamins and minerals. Wrn null mice had significantly increased body weights, increased serum insulin levels, impaired glucose tolerance, and insulin resistance during 4 months of eating the diabetogenic diet. Diffuse fatty infiltration of the liver and pancreatic islet hyperplasia was characteristic morphological features. These observations suggest that Wrn null mice have impaired glucose homeostasis and fat metabolism, and may be a useful model to investigate metabolic conditions associated with aging.

Insulin receptors in mouse brain: Reversibility of age-related impairments by a thymic extract

Recently, we have shown that insulin receptors (InsRs) in the brain undergo impairments with aging. Interestingly, age-related alterations of brain InsRs, are not irreparable as thymus grafts are able to recover them. With the present study we verified the possibility that an aqueous extract from calf thymus (TME) can mimic the restoring action of age-related impairments induced by thymus graft. InsR characteristics were assayed in a group of 25 months old BALB/c-nu mice treated with TME: 2μg/g body weight every third day, for total five subcutaneous injections. The last dose was injected the day before animals were killed. Other two groups of young (4 months) and old (25 months) mice received saline solution with the same schedule. A two-sites model analysis of receptor data confirms the age-dependent decrease of InsR number and kd previously observed in the high affinity population. Furthermore, a statistically significant recovery of number impairment is shown in TME-treated animals. On the contrary, the characteristics of the low affinity receptor subset show no statistically significant differences among the three animal models studied. TME induced recovery of the age-related changes found in brain InsRs, together with previously observed regulatory action of the same thymic extract on the adrenergic system, suggest that thymic gland does not necessarily have to mutually interact with other controlling systems for maintaining or recoving homeostasis of the complex neuroendocrine network during development and aging.

Mutant insulin receptors in syndromes of insulin resistance

To date, mutations of the insulin receptor remain the only well-established causes of severe insulin resistance. There is a broad correlation between the extent of impairment of signal transduction seen when the mutant receptors are expressed in vitro with the severity of the clinical phenotype. Thus leprechaunism, Rabson-Mendenhall syndrome and Type A insulin resistance appear to represent points on a continuum of severity of receptor dysfunction, rather than completely distinct syndromes. In other syndromes of insulin resistance, insulin receptor abnormalities remain the exception. However, functional studies of expressed naturally occurring insulin receptor mutations have acted as experiments of nature and greatly aided attempts to dissect the structure-function relationships of the receptor. The next few years will no doubt begin to reveal the contributions made by defects in the post-receptor signalling cascade to the syndromes of insulin resistance in man.