Probes for INSULIN

Fetal bovine serum (FBS) is used commonly in cell culture. Charcoal-stripped FBS (CS-FBS) is used to study androgen responsiveness and androgen metabolism in cultured CaP cells. Switching CaP cells from FBS to CS-FBS may reduce activity of androgen receptor (AR), inhibit cell proliferation, or modulate intracellular androgen metabolism. Removal of proteins by charcoal stripping may cause changes in biological functions. Proteins in FBS and CS-FBS were profiled using an ion current-based quantitative platform consisting of reproducible surfactant-aided precipitation/on-pellet digestion, long-column nano-liquid chromatography (LC) separation, and ion current-based analysis (ICan). A total of 143 proteins were identified in FBS, among which 14 proteins including insulin-like growth factor 2 (IGF-2) and IGF binding protein (IGFBP)-2 and -6 were reduced in CS-FBS. IGF1 receptor (IGF1R) and insulin receptor (IR) were sensitized to IGFs in CS-FBS. IGF1 and IGF2 stimulation fully compensated for the loss of AR activity to maintain cell growth in CS-FBS. Endogenous production of IGF and IGFBPs was verified in CaP cells and clinical CaP specimens. This study provided the most comprehensive protein profiles of FBS and CS-FBS, and offered an opportunity to identify new protein regulators and signaling pathways that regulate AR activity, androgen metabolism and proliferation of CaP cells.

Abstract

AIM/HYPOTHESIS:

Adiponectin (APN), a circulating hormone secreted by mature adipocytes, has been extensively studied because it has beneficial metabolic effects. While many studies have focused on the congenital loss of APN and its effects on systemic body glucose and lipid metabolism, little is known about the effects triggered by acute loss of APN in the adult mouse. We anticipated that genetically induced acute depletion of APN in adult mice would have a more profound effect on systemic metabolic health than congenital deletion of Adipoq, the gene encoding APN, with its associated potential for adaptive responses that may mask the phenotypes.

METHODS:

Mice carrying loxP-flanked regions of Adipoq were generated and bred to the Adipoq (APN) promoter-driven reverse tetracycline-controlled transactivator (rtTA) (APN-rtTA) gene and a tet-responsive Cre line (TRE-Cre) to achieve acute depletion of APN. Upon acute removal of APN in adult mice, systemic glucose and lipid homeostasis were assessed under basal and insulinopenic conditions.

RESULTS:

The acute depletion of APN results in more severe systemic insulin resistance and hyperlipidaemia than in mice with congenital loss of APN. Furthermore, the acute depletion of APN in adult mice results in a much more dramatic reduction in survival rate, with 50% of inducible knockouts dying in the first 5 days under insulinopenic conditions compared with 0% of congenital Adipoq knockout mice under similar conditions.

CONCLUSIONS/INTERPRETATION:

Acute systemic removal of APN results in a much more negative metabolic phenotype compared with congenital knockout of Adipoq. Specifically, our data demonstrate that acute depletion of APN is especially detrimental to lipid homeostasis, both under basal and insulinopenic conditions. This suggests that compensatory mechanisms exist in congenital knockout mice that offset some of the metabolic actions covered by APN.