Summary Cardiac stimulation via sympathetic neurons can potentially trigger arrhythmias. We present approaches to study neuron-cardiomyocyte interactions involving optogenetic selective probing and all-optical electrophysiology to measure activity in an automated fashion. Here we demonstrate the utility of optical interrogation of sympathetic neurons and their effects on macroscopic cardiomyocyte network dynamics to address research targets such as the effects of adrenergic stimulation via the release of neurotransmitters, the effect of neuronal numbers on cardiac behavior, and the applicability of optogenetics in mechanistic in vitro studies. As arrhythmias are emergent behaviors that involve the coordinated activity of millions of cells, we image at macroscopic scales to capture complex dynamics. We show that neurons can both decrease and increase wave stability and re-entrant activity in culture depending on their induced activity—a finding that may help us understand the often conflicting results seen in experimental and clinical studies.
Neonatal Marfan syndrome (nMFS) is a rare condition with a poor prognosis. It is genotypically and phenotypically distinct from the typical Marfan syndrome and carries a poorer prognosis. This case report describes the progression of a 14-month-old girl diagnosed with nMFS at 5 months of age. Her diagnosis followed the identification of a fibrillin-1 mutation (FBN1 gene, exon 26, chromosome 15), which is a common locus of nMFS. This patient developed severe cardiac complications resulting in congestive cardiac failure in early life and required major cardiac surgery. Since surgical intervention, our patient is still reliant on a degree of ventilator support, but the patient has gained weight and echocardiography has demonstrated improved left ventricular function and improved tricuspid and mitral valve regurgitation. Therefore, we argue the importance of a cautious multidisciplinary approach to early surgical intervention in cases of nMFS.
Alterations in autonomic function are known to occur in cardiac conditions including sudden cardiac death. Cardiac stimulation via sympathetic neurons can potentially trigger arrhythmias. Dissecting direct neural-cardiac interactions at the cellular level is technically challenging and understudied due to the lack of experimental model systems and methodologies. Here we demonstrate the utility of optical interrogation of sympathetic neurons and their effects on macroscopic cardiac monolayer dynamics to address research targets such as the effects of adrenergic stimulation via the release of neurotransmitters, the effect of neuronal numbers on cardiac wave behaviour and the applicability of optogenetics in mechanistic in vitro studies. We combine photo-uncaging or optogenetic neural stimulation with imaging of cardiac monolayers to measure electrical activity in an automated fashion, illustrating the power and high throughput capability of such interrogations. The methods described highlight the challenges and benefits of co-cultures as experimental model systems. RESULTS:1] Stellate Sympathetic Neurons make contacts with cardiomyocytes: Scanning electron microscopy of sympathetic neurons growing in co-culture with cardiomyocytes in vitro shows connections between neurite extension and cardiac syncytium (Figure 1 A). The neuron bodies and extensions clearly make physical contact with myocytes (Figure 1 B, C, D, E, F, G, H, I, J). Immuno staining of co-cultures shows co-localisation of Synpasin and Beta2 receptors (Figure 1 K), sympathetic neurons show positive staining for Th (Figure 1 L), and fibronectin contamination in the co-cultures was assessed by staining with Vimentin (Figure 1 M), which showed low abundance. 2] Pattern formation is affected by the presence of neurons: Using dye-free imaging (Figure 2 A, B, C), we investigated how neuronal activation modulates cardiac patterns of activation in monolayer culture. We chose experimental conditions that spontaneously yield a wide variety of wavefront topologies within the imaging system's 16 x 16 mm field of view. Introduction of an additional cell type can potentially introduce heterogeneities that would impact wave front stability. Surprisingly, co-cultures displayed fewer wave breaks than their monoculture counterparts at similar plating densities (Figure 2 D). We broadly classified wave dynamics as simple (periodic target waves and single spiral wave reentry, Figure 2 D top row), or complex (single dominant spirals with additional irregular waves and multiple equally sized wavelets, Figure 2 D bottom row). While monocultures frequently displayed complex dynamics, co-cultures rarely displayed this behavior (Figure 2 E, P<0.05, chi-square test). Indeed, we observed wavelet reentry in only one of the co-culture preparations (6 isolations, 20 preparations). 3] Conduction velocity in spontaneously active co-cultures is faster than myocyte monocultures:We measured conduction velocity in unstimulated co-cultures (n=19) and myocyte monocultures (n=9). Figure 2 F s...
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