RESUMEN
It is proposed that the impaired counterregulatory response (CRR) to hypoglycemia in insulin-deficient diabetes may be due to chronic brain insulin deficiency. To test this hypothesis, streptozotocin-induced diabetic Sprague-Dawley rats were infused with insulin (3 mU/day) or artificial cerebrospinal fluid (aCSF) bilaterally into the ventromedial hypothalamus (VMH) for 2 wk and compared with nondiabetic rats. Rats underwent hyperinsulinemic (50 mU·kg-1·min-1)-hypoglycemic (~45 mg/dl) clamps. Diabetic rats demonstrated an impaired CRR to hypoglycemia, noted by a high glucose infusion rate and blunted epinephrine and glucagon responses. The defective sympathoadrenal response was restored by chronic infusion of insulin into the VMH. Diabetic rats had decreased VMH Akt phosphorylation and decreased VMH glucose transporter 4 (GLUT4) content, which was also restored by chronic infusion of insulin into the VMH. Separate experiments in nondiabetic rats in which GLUT4 translocation into the VMH was inhibited with an infusion of indinavir were notable for an impaired CRR to hypoglycemia, indicated by increased glucose infusion rate and diminished epinephrine and glucagon responses. Results suggest that, in this model of diabetes, VMH insulin deficiency impairs the sympathoadrenal response to hypoglycemia and that chronic infusion of insulin into the VMH is sufficient to normalize the sympathoadrenal response to hypoglycemia via restoration of GLUT4 expression in the VMH.
Asunto(s)
Glucemia/metabolismo , Diabetes Mellitus Experimental/metabolismo , Transportador de Glucosa de Tipo 4/metabolismo , Hipoglucemia/metabolismo , Hipoglucemiantes/farmacología , Insulina/farmacología , Núcleo Hipotalámico Ventromedial/efectos de los fármacos , Animales , Epinefrina/sangre , Glucagón/sangre , Técnica de Clampeo de la Glucosa , Masculino , Ratas , Ratas Sprague-Dawley , Núcleo Hipotalámico Ventromedial/metabolismoRESUMEN
It is proposed that the impaired sympathoadrenal response to hypoglycemia induced by recurrent insulin-induced hypoglycemia (RH) is an adaptive phenomenon induced by specific changes in microRNA expression in the ventromedial hypothalamus (VMH). To test this hypothesis, genome-wide microRNAomic profiling of the VMH by RNA-sequencing was performed in control rats and rats treated for RH. Differential expression analysis identified microRNA-7a-5p and microRNA-665 as potential mediators of this phenomenon. To further test this hypothesis, experiments were conducted consisting of targeted lentiviral-mediated overexpression of microRNA-7a-5p and downregulation of microRNA-665 in the VMH. Hyperinsulinemic hypoglycemic clamp experiments demonstrated that targeted overexpression of microRNA-7a-5p (but not downregulation of microRNA-665) in the VMH of RH rats restored the epinephrine response to hypoglycemia. This restored response to hypoglycemia was associated with a restoration of GABAA receptor gene expression. Finally, a direct interaction of microRNA-7a-5p with the 3'-UTR of GABAA receptor α1-subunit (Gabra1) gene was demonstrated in a luciferase assay. These findings indicate that (a) the impaired sympathoadrenal response RH induces is associated with changes in VMH microRNA expression and (b) microRNA-7a-5p, possibly via direct downregulation of GABA receptor gene expression, may serve as a mediator of the altered sympathoadrenal response to hypoglycemia.