A euglycaemic/non-diabetic perinatal environment does not alleviate early beta cell maldevelopment and type 2 diabetes risk in the GK/Par rat model

AIMS/HYPOTHESIS

We used the GK/Par rat, a spontaneous model of type 2 diabetes with early defective beta cell neogenesis, to determine whether the development of GK/Par offspring in a non-diabetic intrauterine/postnatal environment would prevent the alteration of fetal beta cell mass (BCM) and ultimately decrease the risk of diabetes later in adult life.

METHODS

We used an embryo-transfer approach, with fertilised GK/Par ovocytes (oGK) being transferred into pregnant Wistar (W) or GK/Par females (pW and pGK). Offspring were phenotyped at fetal age E18.5 and at 10 weeks of age, for BCM, expression of genes of pancreatic progenitor cell regulators (Igf2, Igf1r, Sox9, Pdx1 and Ngn3), glucose tolerance and insulin secretion.

RESULTS

(1) Alterations in neogenesis markers/regulators and BCM were as severe in the oGK/pW E18.5 fetuses as in the oGK/pGK group. (2) Adult offspring from oGK transfers into GK (oGK/pGK/sGK) had the expected diabetic phenotype compared with unmanipulated GK rats. (3) Adult offspring from oGK reared in pW mothers and milked by GK foster mothers had reduced BCM, basal hyperglycaemia, glucose intolerance and low insulin, to an extent similar to that of oGK/pGK/sGK offspring. (4) In adult offspring from oGK transferred into pW mothers and milked by their W mothers (oGK/pW/sW), the phenotype was similar to that in oGK/pGK/sGK or oGK/pW/sGK offspring.

CONCLUSIONS/INTERPRETATION

These data support the conclusion that early BCM alteration and subsequent diabetes risk in the GK/Par model are not removed despite normalisation of the prenatal and postnatal environments, either isolated or combined.

Islet structure and function in the GK rat

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of beta-cell secretory dysfunction and/or decreased beta-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto-Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK islet abnormalities so far identified is proposed in this perspective. The pathogenesis of defective beta-cell number and function in the GK model is also discussed. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (i) several susceptibility loci containing genes responsible for some diabetic traits (distinct loci encoding impairment of beta-cell metabolism and insulin exocytosis, but no quantitative trait locus for decreased beta-cell mass); (ii) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas (decreased beta-cell neogenesis and proliferation) transmitted over generations; and (iii) loss of beta-cell differentiation related to chronic exposure to hyperglycaemia/hyperlipidaemia, islet inflammation, islet oxidative stress, islet fibrosis and perturbed islet vasculature.

The relationship between p38 mitogen-activated protein kinase and AMP-activated protein kinase during myocardial ischemia

OBJECTIVE

p38 mitogen-activated protein kinase (p38 MAPK) and AMP-activated protein kinase (AMPK) are activated by, and influence sensitivity to, myocardial ischemia. Recently a number of studies have suggested that AMPK may participate in the activation of p38 MAPK. We therefore examined whether AMPK may be the principal "ischemia sensor" responsible for p38 MAPK activation during myocardial ischemia.

METHODS

We used a variety of approaches to alter AMPK activity during ischemia and studied the repercussions on p38 MAPK activation.

RESULTS

The activities of AMPK and p38 MAPK were temporally related in adult rat ventricular myocytes (ARVM) subjected to simulated ischemia and in isolated mouse hearts subjected to no-flow ischemia. However p38 MAPK activation was unaltered in mouse hearts lacking the predominant or minor myocardial isoforms, AMPKalpha2 or AMPKalpha1 respectively. Likewise, in ARVM, adenoviral-driven expression of the minor myocardial isoform AMPKalpha1, in a constitutively active or dominant negative form reducing AMPK activity, did not alter p38 MAPK activation under basal conditions or during simulated ischemia. Finally, pharmacological inhibition of AMPK during ischemia with compound C did not attenuate the coincident activation of p38 MAPK.

CONCLUSIONS

Although AMPK and p38 MAPK are both activated during myocardial ischemia, the activation of p38 MAPK occurs independently of AMPK.