Role of sympathetic neurons in the control of cardiac cells

The functional and structural interaction of cardiac sympathetic neurons (SN) with resident myocardial cell types, including cardiomyocytes (CM) and cardiac fibroblasts (CF) is a matter of high significance in heart physiology and potential translational impact in cardiovascular sciences. The work of my PhD course has focused on the study of the neuro-cardiac interaction and the effects cardiac autonomic neurons may play at molecular and cellular level on the muscular and non-muscle components of the heart. To achieve deeper understanding on the physiology and biophysics underlying neuro-cardiac communication, I used a variety of methods i) FRET fluorescence imaging, for dynamic investigation of how biochemical parameters in cardiomyocytes and fibroblasts are influenced by the activity of sympathetic neurons (i.e. neurotransmitter-dependent second messenger signaling, Ca2+, cAMP); ii) state of the art imaging methods (i.e. scanning ion conductance microscopy), to characterize the structure of the SN/CM intercellular interaction sites; iii) confocal microscopy, to gain high resolution information on the cellular localization of proteins involved in neuro-cardiac intercellular signaling. Most of the work I have performed has been based on initial development of a novel protocol, to optimize the preparation of primary cultured cardiomyocytes from rodent hearts, which represented an in vitro model well suited for the analyses performed in the all remainder parts of the work. The work demonstrates that signaling between sympathetic neuron and cardiomyocytes occurs via direct interaction at the Neuro Cardiac Junction (NCJ) and that that synaptic signaling is restricted to the cells in direct contact. Sympathetic neuron survival mechanisms participate, when defective, to several cardiac pathologies. Retrograde signaling from CMs to SNs is critical for neuronal survival and development. We here provide in vitro and ex vivo evidence that NGF input to SN occurs at NCJs, and show the effect of specialized signaling sites on retrograde neurotrophic signaling and neuronal survival. Furthermore, pharmacologic assays demonstrated that the unconventional sympathetic neurotransmitter, Neuropeptide Y (NPY), has a role in regulating cardiac fibroblast proliferation and differentiation and may thus have a role in myocardial fibrosis. The results of the experiments described in this thesis, increase our understanding of cardiac regulatory mechanisms, and lay the grounds basis to uncover whether alteration of local neuro-cardiac communication may underlie common heart diseases, including heart failure and arrhythmias