Pathophysiological Cardiac Remodeling And The Potential Of Cellular And Molecular Therapy

Pathological cardiac remodeling occurs following myocardial injury and results in impaired cardiac function. Cellular therapy involving stem cell transplantation has been shown to attenuate the effects of cardiac remodeling and improve cardiac function. Mesenchymal stem cells (MSCs) are known to alleviate arrhythmias and improve conduction when transplanted into cardiac tissue; however, the mechanism was not yet determined. Therefore, the first objective of the study was aimed to determine the mechanism by which MSCs modulate the excitability and conduction in cardiac tissue after transplantation by testing the hypothesis that MSCs modulate conduction i. by intercellular coupling with cardiomyocytes or ii. by paracrine signaling. Multi-electrode arrays (MEAs) were used to monitor beating frequency and conduction velocity (θ) in HL-1 cardiomyocyte monolayers in vitro. Co-culture of MSCs with HL-1 cells significantly attenuated the beating frequency over time with no significant change in θ. However, treatment of HL-1 cells with MSC-conditioned media/tyrode (ConM/ConT) significantly enhanced θ over time with no change in excitability. Further results demonstrated that connexin 43 (Cx43) expression was upregulated after treatment with ConM/ConT. This upregulation was dependent on the activation of Wnt signaling pathway in part through MSC-dependent Wnt secretion. Overall the results indicate that MSCs decrease cardiomyocyte excitability via hetero-cellular coupling and increase cardiac conduction by upregulation of Cx43 via paracrine signaling. The second objective of the thesis involved studying transverse-tubule (T-tubule) remodeling during pathological cardiac remodeling. T-tubules are cellular structures that enable synchronous calcium release and uniform contraction across the entire myocyte. Although it is known that t-tubules undergo remodeling under pathological conditions such as hypertrophy and heart failure (HF), the mechanisms underlying this are not clearly understood. Therefore, we aimed to determine the mechanism by which t-tubule remodeling occurs. T-tubule integrity was assessed using confocal microscopy. The initial experimental results indicate that inhibition of NADPH oxidase, a reactive oxygen species (ROS) producer, attenuates t-tubular remodeling. Therefore, this initial study demonstrates ROS as a potential target to attenuate t-tubular remodeling during pathological conditions

Data from: Cross-modal influence of mechanosensory input on gaze responses to visual motion in Drosophila

Animals typically combine inertial and visual information to stabilize their gaze against confounding self-generated visual motion, and to maintain a level gaze when the body is perturbed by external forces. In vertebrates, an inner ear vestibular system provides information about body rotations and accelerations, but gaze stabilization is less understood in insects, which lack a vestibular organ. In flies, the halteres, reduced hindwings imbued with hundreds of mechanosensory cells, sense inertial forces and provide input to neck motoneurons that control gaze. These neck motoneurons also receive input from the visual system. Head movement responses to visual motion and physical rotations of the body have been measured independently, but how inertial information might influence gaze responses to visual motion has not been fully explored. We measured the head movement responses to visual motion in intact and haltere-ablated tethered flies to explore the role of the halteres in modulating visually guided head movements in the absence of rotation. We note that visually guided head movements occur only during flight. Although halteres are not necessary for head movements, the amplitude of the response is smaller in haltereless flies at higher speeds of visual motion. This modulation occurred in the absence of rotational body movements, demonstrating that the inertial forces associated with straight tethered flight are important for gaze-control behavior. The cross-modal influence of halteres on the fly's responses to fast visual motion indicates that the haltere's role in gaze stabilization extends beyond its canonical function as a sensor of angular rotations of the thorax

Data from: Kinematic diversity suggests expanded roles for fly halteres

The halteres of flies are mechanosensory organs that provide information about body rotations during flight. We measured haltere movements in a range of fly taxa during free walking and tethered flight. We find a diversity of wing–haltere phase relationships in flight, with higher variability in more ancient families and less in more derived families. Diverse haltere movements were observed during free walking and were correlated with phylogeny. We predicted that haltere removal might decrease behavioural performance in those flies that move them during walking and provide evidence that this is the case. Our comparative approach reveals previously unknown diversity in haltere movements and opens the possibility of multiple functional roles for halteres in different fly behaviours

Walking flies filmed with two cameras

These are two-dimensional coordinates of both halteres of walking flies as filmed with two cameras. The tip and base of each haltere is digitized, as well as the thorax (as a metric of body position) and one of the legs

Digitized traces of wing and haltere tip in flying flies

These files contain two-dimensional coordinates for the tip and base of both the haltere and the wing in tethered flying flies

Perturbation videos

Perturbation video