Abstract 146: Long Term Effect of nNOS Overexpression on Cardiac Neurotransmission Mediated by Lentiviral Vector
Several cardiovascular pathologies are associated with cardiac autonomic impairment that may lead to arrhythmia and sudden death. Gene transfer of neuronal nitric oxide synthase (nNOS) into local cardiac neurons can either increase vagal neurotransmission or inhibit sympathetic neurotransmission. We investigated the long term effect of nNOS up-regulation on cardiac sympatho-vagal balance mediated by a lentiviral vector. We developed a lentiviral vector with an elongation factor 1 α (EF1α) promoter to drive nNOS or eGFP expression. Lenti.EF1α-nNOS or Lenti.EF1α-eGFP was transferred to the right atrium of Spague-Dawley rats. Persistent nNOS over-expression in intracardiac ganglia was observed after 4 months of gene transfer by Western Blot. Lenti.EF1α-nNOS transduction caused a 58.8% increase in nNOS gene expression compared to Lenti.EF1α-eGFP transduced atria (n=7 in each group, p<0.01, unpaired t-test). Atrial cGMP level was increased by 34.4% in Lenti.EF1α-nNOS transduced atria compared to eGFP group, (n=8 in each group, p<0.05, unpaired t-test). We also observed that cAMP level in the nNOS gene transferred group was increased 26.7% compared to eGFP group (n=8 in each group, p<0.05, unpaired t-test). To determine the effect of nNOS on cardiac parasympathetic or sympathetic neurotransmission, we measured acetylcholine (ACh) or norepinephrine (NE) release to field stimulation in both groups. nNOS transduced animals displayed enhanced ACh release (97.1 %, n=7, p<0.05, unpaired t-test) and reduced NE release (32.8 %, n=6, p<0.05, unpaired t-test) compared to eGFP group (n=5). nNOS specific inhibition reversed the enhanced ACh release. These results suggest that persistent cardiac nNOS up-regulation mediated by a lentiviral vector not only facilitates parasympathetic neurotransmission through activating NO-cGMP pathway on postganglionic cardiac cholinergic neurons, but also inhibits sympathetic neurotransmission through varicosities of intrinsic cardiac adrenergic cells since this viral vector does not travel retrogradely. This viral-mediated gene transfer strategy enables us to monitor cardiac sympatho-vagal balance over the long term to establish whether disease states might be affected.