Urocortin 2 Gene Transfer Reduces the Adverse Effects of a Western Diet on Cardiac Function in Mice

Corticotropin-releasing hormone and obesity: From fetal life to adulthood

Obesity is among the most common chronic disorders, worldwide. It is a complex disease that reflects the interactions between environmental influences, multiple genetic allelic variants, and behavioral factors. Recent developments have also shown that biological conditions in utero play an important role in the programming of energy homeostasis systems and might have an impact on obesity and metabolic disease risk. The corticotropin-releasing hormone (CRH) family of neuropeptides, as a central element of energy homeostasis, has been evaluated for its role in the pathophysiology of obesity. This review aims to summarize the relevance and effects of the CRH family of peptides in the pathophysiology of obesity spanning from fetal life to adulthood.

Effects of Urocortin 2 Gene Transfer on Glucose Disposal in Insulin-Resistant db/db Mice on Metformin

The study was designed to determine whether urocortin 2 (Ucn2) gene transfer is as safe and effective as metformin in insulin-resistant mice. Four groups of insulin-resistant db/db mice and a nondiabetic group were studied: (1) metformin; (2) Ucn2 gene transfer; (3) metformin + Ucn2 gene transfer; (4) saline; and (5) nondiabetic mice. After completion of the 15-week protocol, glucose disposal was quantified, safety assessed, and gene expression documented. Ucn2 gene transfer was superior to metformin, providing reductions in fasting glucose and glycated hemoglobin and enhanced glucose tolerance. The combination of metformin + Ucn2 gene transfer provided no better glucose control than Ucn2 gene transfer alone and was not associated with hypoglycemia. Metformin alone, Ucn2 gene transfer alone, and metformin + Ucn2 gene transfer together reduced fatty infiltration of the liver. Serum alanine transaminase concentration was elevated in all db/db groups (vs. nondiabetic controls), but the metformin + Ucn2 gene transfer combined group had the lowest alanine transaminase levels. No group differences in fibrosis were detected. In a hepatoma cell line, activation of AMP kinase showed a rank order of combined metformin + Ucn2 peptide > Ucn2 peptide > metformin. We conclude (1) The combination of metformin + Ucn2 gene transfer does not result in hypoglycemia. (2) Ucn2 gene transfer alone provides superior glucose disposal versus metformin alone. (3) The combination of Ucn2 gene transfer and metformin is safe and has additive effects in reducing serum alanine transaminase concentration, activating AMP kinase activity, and increasing Ucn2 expression, but is no more efficacious than Ucn2 gene transfer alone in reducing hyperglycemia. These data indicate that Ucn2 gene transfer is more effective than metformin in the db/db model of insulin resistance and combined treatment with metformin + Ucn2 gene transfer appears to have favorable effects on liver function and Ucn2 expression.

Urocortin 2 Gene Transfer for Systolic and Diastolic Dysfunction Due to Chronically Increased Left Ventricular Pressure

We used transverse aortic constriction (TAC) in mice to test the hypothesis that urocortin 2 (Ucn2) gene transfer would increase left ventricular (LV) systolic and diastolic function in the pressure-stressed LV. Three groups were studied: (1) control mice (no TAC); (2) mice that received saline 6 weeks after TAC; and (3) mice that received Ucn2 gene transfer 6 weeks after TAC, using adeno-associated virus 8 encoding murine Ucn2 (AAV8.mUcn2; 2 × 1013 genome copies (gc)/kg, i.v. per mouse). Echocardiography was performed 6 and 12 weeks after TAC. In terminal studies 12 weeks after TAC, rates of LV pressure development and decay and Tau were measured, and LV cardiac myocytes (CMs) were isolated and cytosolic Ca2+ transients and sarcomere shortening rates recorded. Reverse transcription polymerase chain reaction and immunoblotting were used to measure key proteins in LV samples. A CM cell line (HL-1) was used to explore mechanisms. Concentric LV hypertrophy was evident on echocardiography 6 weeks after TAC. Twelve weeks after TAC, LV ejection fraction (EF) was higher in mice that received Ucn2 gene transfer (TAC-saline: 65% ± 3%; TAC-Ucn2: 75% ± 2%; p = 0.01), as was LV peak +dP/dt (1.9-fold increase; p = 0.001) and LV peak -dP/dt (1.7-fold increase; p = 0.017). Tau was more rapid (23% reduction, p = 0.02), indicating improved diastolic function. The peak rates of sarcomere shortening (p = 0.002) and lengthening (p = 0.002) were higher in CMs from TAC-Ucn2 mice, and Tau was reduced (p = 0.001). LV (Ser-16) phosphorylation of phospholamban (PLB) was increased in TAC-Ucn2 mice (p = 0.025), and also was increased in HL-1 cells treated with angiotensin II to induce hypertrophy and incubated with Ucn2 peptide (p = 0.001). Ucn2 gene transfer in TAC-induced heart failure with preserved ejection fraction increased cardiac function in the intact LV and provided corresponding benefits in CMs isolated from study animals, including increased myofilament Ca2+ sensitivity during contraction. The mechanism includes enhanced CM Ca2+ handling associated with increased (Ser-16)-PLB.

Significant alteration of liver metabolites by AAV8.Urocortin 2 gene transfer in mice with insulin resistance

INTRODUCTION

Urocortin 2 (Ucn2) is a 38-amino acid peptide of the corticotropin-releasing factor family. Intravenous (IV) delivery of an adeno-associated virus vector serotype 8 encoding Ucn2 (AAV8.Ucn2) increases insulin sensitivity and glucose disposal in mice with insulin resistance.

OBJECTIVE

To determine the effects of Ucn2 on liver metabolome.

METHODS

Six-week-old C57BL6 mice were divided into normal chow (CHOW)-fed and high fat diet (HFD)-fed groups. The animals received saline, AAV8 encoding no gene (AAV8.Empt) or AAV8.Ucn2 (2x1013 genome copy/kg, IV injection). Livers were isolated from CHOW-fed and HFD-fed mice and analyzed by untargeted metabolomics. Group differences were statistically analyzed.

RESULTS

In CHOW-fed mice, AAV8.Ucn2 gene transfer (vs. saline) altered the metabolites in glycolysis, pentose phosphate, glycogen synthesis, glycogenolysis, and choline-folate-methionine signaling pathways. In addition, AAV8.Ucn2 gene transfer increased amino acids and peptides, which were associated with reduced protein synthesis. In insulin resistant (HFD-induced) mice, HFD (vs CHOW) altered 448 (112 increased and 336 decreased) metabolites and AAV8.Ucn2 altered 239 metabolites (124 increased and 115 reduced) in multiple pathways. There are 61 metabolites in 5 super pathways showed interactions between diet and AAV8.Ucn2 treatment. Among them, AAV8.Ucn2 gene transfer reversed HFD effects on 13 metabolites. Finally, plasma Ucn2 effects were determined using a 3-group comparison of HFD-fed mice that received AAV8.Ucn2, AAV.Empt or saline, where 18 metabolites that altered by HFD (15 increased and 3 decreased), but restored levels to that seen in CHOW-fed mice by increased plasma Ucn2.

CONCLUSIONS

Metabolomics study revealed that AAV8.Ucn2 gene transfer, through increased plasma Ucn2, provided counter-HFD effects in restoring hepatic metabolites to normal levels, which could be the underlying mechanisms for Ucn2 effects on increasing glucose disposal and reducing insulin assistance.