Abstract Body (Do not enter title and authors here): Background: Duchenne muscular dystrophy (DMD) is a recessive X-linked neuromuscular disorder resulting from a mutation in the dystrophin gene. Loss of dystrophin within cardiomyocytes results in cell death leading to myocardial fibrosis and cardiomyopathy. Vasoactive intestine peptide (VIP) is the most abundant neuropeptide within the cardiopulmonary system including the heart, and its binding to VIP receptors results in activation of cAMP-PKA signaling in the cardiac myocytes. The mechanism remains unclear.
Methods and Results: Utilizing physiological, histological and molecular techniques, we assessed the ability of PB1046, a cardiac specific VIP analog, to prevent cardiac dysfunction in 3 mouse models (WT, mdx, and mdx:Utrn^+/-, n=10-12). Two dosages were applied for PB1046 (low dose: 0.75mg/kg; high dose: 1.5mg/kg). The drug was injected subcutaneously every other day starting at 4 weeks of age for a total of 8 weeks. Cardiac function was assessed weekly using echocardiography. After 8 weeks of high dose PB1046 treatment, there was a preservation of cardiac function in mdx:Utrn^+/- mice, while the mice receiving placebo (saline) developed significant reduction in cardiac function (FS: 61%±0.4 vs 45%±1.3, n=10-12, P<0.01). The fibrosis in the hearts from mdx:Utrn^+/- mice treated with high dose PB1046 was significantly reduced as compared to placebo (2.92%±0.13 vs 6.42%±0.39, n=3, P<0.05), which was consistent with decreased HO-proline levels in the heart tissues (41.6±3.7 vs 64.3±6.9 nmol/100mg heart weight, n=6, P<0.05). RNA-Seq data indicated the majority of transcripts of cAMP signaling were upregulated whereas the transcripts of NF-kB signaling were downregulated in isolated cardiac myocytes. Activation of cAMP signaling was confirmed by the elevated cAMP level in the hearts (33.8±6.5 vs 15.3±3.4 pmol/mg proteins, n=6-8, P<0.05) and CREB phosphorylation levels in nucleus (1.97±0.35 vs 1.00±0.06, n=4-6, P<0.05) by high dose PB1046 treatment compared with placebo. Downregulation of NF-kB signaling was demonstrated by the significantly reduced phosphorylation level of NF-kB p65 in cardiac-specific nuclear fractions from mdx:Utrn^+/- mice treated with high dose PB1046 compared with placebo (0.62±0.06 vs 1.00±0.09, n=3-5, P<0.01).
Conclusions: Collectively, the study data suggests augmentation of cardiac-specific VIP signaling prevents cardiac dysfunction through inhibition of NF-kB signaling in a murine model of DMD.