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Myocardial infarction (MI)-induced ventricular arrhythmia is the most common cause of death in patients with type 2 diabetes mellitus (T2DM). Patients with T2DM are two to four times more likely to die from MI than non-diabetic patients. Withdrawal of cardiac vagal activity is an important trigger for MI-induced ventricular arrhythmias in T2DM. Our recent study found that T2DM-elevated hydrogen peroxide (H2O2) levels in cardiac vagal postganglionic (CVP) neurons contribute to the withdrawal of cardiac vagal activity and ventricular arrhythmogenesis through inhibition of N-type Ca2+ channels (Cav2.2) in CVP neurons. The repressor element 1-silencing transcription factor (REST) is crucial to inhibit the expression of Cav2.2-α. In general, mature neuronal cells do not express the REST in the physiological condition. Here, we tested whether H2O2 induces REST expression in CVP neurons, which successively inhibits the expression of Cav2.2 in CVP neurons, causes cardiac vagal dysfunction, and triggers MI-evoked ventricular arrhythmias in T2DM rats. Our in vitro experiments demonstrated that protein expression of REST is high, whereas Cav2.2-α expression is low in undifferentiated NG108-15 cells. Differentiation of NG108-15 cells for twenty-one days significantly reduced REST expression and increased Cav2.2-α expression. Additionally, treatment with exogenous H2O2 (1 μM) in differentiated NG108-15 cells markedly increased REST expression and decreased Cav2.2-α expression. Similarly, a high level of REST protein and a low level of Cav2.2-α protein were confirmed in CVP neurons from T2DM rats than those from age-matched sham rats. In vivo transfection of REST shRNA (2 μl, 1×107 TU/ml) into the CVP neurons significantly decreased REST expression and increased Cav2.2-α expression in CVP neurons from T2DM rats. REST shRNA also improved cardiac vagal function, measured by heart rate variability, and reduced the cumulative duration of MI-evoked ventricular arrhythmias in conscious rats. These data suggested that H2O2-REST signaling pathway could be a key factor to mediate cardiac vagal dysfunction and affect the occurrence of ventricular arrhythmias in T2DM. This study was supported by the NIH-NHLBI (R01HL144146 to YLL). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Withdrawal of cardiac vagal activity is associated with ventricular arrhythmias-related sudden cardiac death and high mortality in T2DM patients. Although vagal nerve stimulation (VNS) has emerged as a promising therapy for ventricular arrhythmias, VNS-induced off-target side effects due to a lack of organ specificity severely limit its prescription in the clinic. To avoid the limitations of the VNS, we employed an optogenetic technique that combines with a miniaturized bio-optoelectronic implant with genetic targeting strategies to achieve cardiac-specific vagal activation in T2DM rats. We hypothesize that optogenetic activation in cardiac vagal postganglionic (CVP) neurons can restore vagal control of cardiac function, and further reduce susceptibility to ventricular arrhythmias in T2DM. Rat T2DM was induced by a high-fat diet plus streptozotocin injection. AAV-channelrhodopsin-2 (ChR2, 2 μl, 5x1012 vg/ml), an excitatory light-sensitive opsin gene, was in vivo transfected into CVP neurons located in the atrioventricular ganglion (AVG). At three weeks after opsin gene (i.e., AAV-ChR2) transfection, continual optogenetic stimulation in CVP neurons was applied twice daily (10 Hz, 50% duty cycle, 5 mW for 1 hour) by illuminating a LED probe that is controlled and powered wirelessly in conscious rats. Our data from immunofluorescence staining showed that microinjection of AAV-ChR2 into the AVG induced expression of ChR2-mcherry in almost all CVP neurons. Optogenetic activation of CVP neurons resulted in a negative inotropic reaction on the left ventricular systolic pressure in a frequency-dependent manner in anesthetized rats. Data from spectral analysis of heart rate variability demonstrated that optogenetic stimulation gradually restored T2DM-reduced high-frequency power (an index of cardiac vagal activation) from one to three days after optogenetic therapy in vivo, whereas it has no effect on low-frequency power (an index of cardiac sympathetic activation). Additionally, data from 24-hour continuous ECG recording in conscious rats demonstrated that optogenetic stimulation in CVP neurons improved the T2DM-impaired heterogeneity of ventricular electrical activity, which was measured by evaluating ventricular arrhythmia-related ECG parameters at three days after optogenetic therapy in vivo. These data suggested that optogenetic activation in CVP neurons might be an effective intervention against cardiac vagal dysfunction-related ventricular arrhythmias in the T2DM state. This study was supported by the Great Plains IDeA-CTR Pilot Grant (to DZ), NIH-NHLBI (R01HL144146 to YLL), and AHA Career Development Award (851929 to DZ). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.