Insulin hypersecretion in islets from diet-induced obese mice

Insulin hypersecretion in islets from diet-induced hyperinsulinemic obese female mice is associated with several functional adaptations in individual β-cells.

Abstract

Insulin resistance and hyperinsulinemia are generally associated with obesity. Obese nondiabetic individuals develop a compensatory β-cell response to adjust insulin levels to the increased demand, maintaining euglycemia. Although several studies indicate that this compensation relies on structural changes, the existence of β-cell functional adaptations is incompletely understood. Here, we fed female mice with a high-fat diet (HFD) for 12 weeks. These animals became obese, hyperinsulinemic, insulin-resistant, and mildly glucose-intolerant while fed, and fasting glycemia was comparable in HFD and control mice. Islets from HFD animals exhibited increased β-cell mass and hypertrophy.

Additionally, they had enhanced insulin gene expression and content and augmented glucose-induced insulin secretion. Electrophysiological examination of β-cells from both groups showed no differences in KATP channel open probability and conductance. However, action potentials elicited by glucose had larger amplitude in obese mice. Glucose-induced Ca²⁺ signals in intact islets, in isolated β-cells, and individual β-cells within islets were also increased in HFD mice. Additionally, a higher proportion of glucose-responsive cells was present in obese mice. In contrast, whole-cell Ca²⁺ current densities were similar in both groups.

Capacitance measurements showed that depolarization-evoked exocytosis was enhanced in HFD β-cells compared with controls. Although this augment was not significant when capacitance increases of the whole β-cell population were normalized to cell size, the exocytotic output varied significantly when β-cells were distributed by size ranges. All these findings indicate that β-cell functional adaptations are present in the islet compensatory response to obesity.

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Found this in a related link to JJ's 2012 paper on hyperinsulinemia, very interesting that obese islets are programmed to secrete large amounts of insulin for a given amount of glucose?

Is this an "adaption" to insulin resistance? I dont believe so. If we go back to JJ's paper we remember that insulin feed's back positively to beta islets via the autocrine loop to cause growth. Possibly also to cause these morphological changes. I think a reasonable assumption is that anything that causes intense insulin secretion will serve to induce these morphological changes and obesity may follow.