The roles of CD38 and NAADP in cardiac tissue

Nicotinic acid adenine dinucleotide phosphate (NAADP) is an endogenous molecule that releases calcium ions (Ca2+) from acidic endolysosomal stores. This Ca2+-mobilising molecule is known to play a role in modulating cardiac excitation-contraction coupling and pathophysiology. The first part of the thesis focuses on understanding the mechanistic details of NAADP actions, particularly during the flight and fight response of the heart. Paced ventricular myocytes, which had genetically- (Tpcn2-/-) or pharmacologically-impaired (bafilomycin-A1 treatment) NAADP signalling pathways, had blunted responses to isoprenaline. Further investigations revealed that NAADP actions are dependent of functional CaMKII proteins but independent of L-type Ca2+ channels. The main part of the thesis focuses on understanding the enzymatic production of NAADP in the heart. Although CD38, which belongs to the ADP-ribosyl cyclase (ARC) family, has been shown to catalyse the synthesis of NAADP in other mammalian tissue, whether CD38 is responsible for the production of NAADP in the heart remains debatable. Membrane fractions from CD38-/- mouse hearts were not able to generate NAADP through catalysing the base-exchange reaction. Experiments involving the permeabilisation of cardiac myocytes also revealed the intracellular expression of CD38 on the sarcoplasmic reticulum (SR). The SR-enriched membrane preparation (SRMP) from sheep heart is also capable of catalysing NAADP production and showed properties associated with those of CD38. Upon isoprenaline addition, paced CD38-/- myocytes had smaller Ca2+ transients and contraction amplitudes, compared to those of wild type animals. In addition, impairing NAADP signalling using bafilomycin-A1 did not affect the effect of isoprenaline on CD38-/- myocytes. highlighting the role of CD38 in coupling NAADP action to beta-adrenoceptor signalling. Lastly, a novel ARC inhibitor, SAN4825, was also shown to inhibit NAADP synthesis in both mouse and sheep cardiac preparations, through targeting CD38. CD38-/- hearts or SAN 4825-treated hearts were resistant to isoprenaline-induced arrhythmias. These observations support the hypothesis that NAADP is generated by intracellular CD38 in the heart, which contributes to the positive inotropic and pro-arrhythmic effects of the beta-adrenoceptor activation

The roles of CD38 and NAADP in cardiac tissue

Nicotinic acid adenine dinucleotide phosphate (NAADP) is an endogenous molecule that releases calcium ions (Ca2+) from acidic endolysosomal stores. This Ca2+-mobilising molecule is known to play a role in modulating cardiac excitation-contraction coupling and pathophysiology. The first part of the thesis focuses on understanding the mechanistic details of NAADP actions, particularly during the flight and fight response of the heart. Paced ventricular myocytes, which had genetically- (Tpcn2-/-) or pharmacologically-impaired (bafilomycin-A1 treatment) NAADP signalling pathways, had blunted responses to isoprenaline. Further investigations revealed that NAADP actions are dependent of functional CaMKII proteins but independent of L-type Ca2+ channels. The main part of the thesis focuses on understanding the enzymatic production of NAADP in the heart. Although CD38, which belongs to the ADP-ribosyl cyclase (ARC) family, has been shown to catalyse the synthesis of NAADP in other mammalian tissue, whether CD38 is responsible for the production of NAADP in the heart remains debatable. Membrane fractions from CD38-/- mouse hearts were not able to generate NAADP through catalysing the base-exchange reaction. Experiments involving the permeabilisation of cardiac myocytes also revealed the intracellular expression of CD38 on the sarcoplasmic reticulum (SR). The SR-enriched membrane preparation (SRMP) from sheep heart is also capable of catalysing NAADP production and showed properties associated with those of CD38. Upon isoprenaline addition, paced CD38-/- myocytes had smaller Ca2+ transients and contraction amplitudes, compared to those of wild type animals. In addition, impairing NAADP signalling using bafilomycin-A1 did not affect the effect of isoprenaline on CD38-/- myocytes. highlighting the role of CD38 in coupling NAADP action to beta-adrenoceptor signalling. Lastly, a novel ARC inhibitor, SAN4825, was also shown to inhibit NAADP synthesis in both mouse and sheep cardiac preparations, through targeting CD38. CD38-/- hearts or SAN 4825-treated hearts were resistant to isoprenaline-induced arrhythmias. These observations support the hypothesis that NAADP is generated by intracellular CD38 in the heart, which contributes to the positive inotropic and pro-arrhythmic effects of the beta-adrenoceptor activation.</p

BDNF-Dependent Plasticity Induced by Peripheral Inflammation in the Primary Sensory and the Cingulate Cortex Triggers Cold Allodynia and Reveals a Major Role for Endogenous BDNF As a Tuner of the Affective Aspect of Pain

International audiencePainful experiences are multilayered, composed of sensory, affective, cognitive and behavioral facets. Whereas it is well accepted that the development of chronic pain is due to maladaptive neuronal changes, the underlying molecular mechanisms, their relationship to the different pain modalities, and indeed the localization of these changes are still unknown. Brain-derived neurotrophic factor (BDNF) is an activity-dependent neuromodulator in the adult brain, which enhances neuronal excitability. In the spinal cord, BDNF underlies the development and maintenance of inflammatory and neuropathic pain. Here, we hypothesized that BDNF could be a trigger of some of these plastic changes. Our results demonstrate that BDNF is upregulated in the anterior cingulate cortex (ACC) and the primary sensory cortex (S1) in rats with inflammatory pain. Injections of recombinant BDNF (into the ACC) or a viral vector synthesizing BDNF (into the ACC or S1) triggered both neuronal hyperexcitability, as shown by elevated long-term potentiation, and sustained pain hypersensitivity. Finally, pharmacological blockade of BDNF-tropomyosin receptor kinase B (TrkB) signaling in the ACC, through local injection of cyclotraxin-B (a novel, highly potent, and selective TrkB antagonist) prevented neuronal hyperexcitability, the emergence of cold hypersensitivity, and passive avoidance behavior. These findings show that BDNF-dependent neuronal plasticity in the ACC, a structure known to be involved in the affective-emotional aspect of pain, is a key mechanism in the development and maintenance of the emotional aspect of chronic pain