Hideaki Kanazawa

Sema3a maintains normal heart rhythm through sympathetic innervation patterning

Sympathetic innervation is critical for effective cardiac function. However, the developmental and regulatory mechanisms determining the density and patterning of cardiac sympathetic innervation remain unclear, as does the role of this innervation in arrhythmogenesis. Here we show that a neural chemorepellent, Sema3a, establishes cardiac sympathetic innervation patterning. Sema3a is abundantly expressed in the trabecular layer in early-stage embryos but is restricted to Purkinje fibers after birth, forming an epicardial-to-endocardial transmural sympathetic innervation patterning. Sema3a−/− mice lacked a cardiac sympathetic innervation gradient and exhibited stellate ganglia malformation, which led to marked sinus bradycardia due to sympathetic dysfunction. Cardiac-specific overexpression of Sema3a in transgenic mice (SemaTG) was associated with reduced sympathetic innervation and attenuation of the epicardial-to-endocardial innervation gradient. SemaTG mice demonstrated sudden death and susceptibility to ventricular tachycardia, due to catecholamine supersensitivity and prolongation of the action potential duration. We conclude that appropriate cardiac Sema3a expression is needed for sympathetic innervation patterning and is critical for heart rate control.

Cardiac Innervation and Sudden Cardiac Death

Afferent and efferent cardiac neurotransmission via the cardiac nerves intricately modulates nearly all physiological functions of the heart (chronotropy, dromotropy, lusitropy, and inotropy). Afferent information from the heart is transmitted to higher levels of the nervous system for processing (intrinsic cardiac nervous system, extracardiac-intrathoracic ganglia, spinal cord, brain stem, and higher centers), which ultimately results in efferent cardiomotor neural impulses (via the sympathetic and parasympathetic nerves). This system forms interacting feedback loops that provide physiological stability for maintaining normal rhythm and life-sustaining circulation. This system also ensures that there is fine-tuned regulation of sympathetic-parasympathetic balance in the heart under normal and stressed states in the short (beat to beat), intermediate (minutes to hours), and long term (days to years). This important neurovisceral/autonomic nervous system also plays a major role in the pathophysiology and progression of heart disease, including heart failure and arrhythmias leading to sudden cardiac death. Transdifferentiation of neurons in heart failure, functional denervation, cardiac and extracardiac neural remodeling has also been identified and characterized during the progression of disease. Recent advances in understanding the cellular and molecular processes governing innervation and the functional control of the myocardium in health and disease provide a rational mechanistic basis for the development of neuraxial therapies for preventing sudden cardiac death and other arrhythmias. Advances in cellular, molecular, and bioengineering realms have underscored the emergence of this area as an important avenue of scientific inquiry and therapeutic intervention.

Macrophages mediate cardioprotective cellular postconditioning in acute myocardial infarction

Ischemic injury in the heart induces an inflammatory cascade that both repairs damage and exacerbates scar tissue formation. Cardiosphere-derived cells (CDCs) are a stem-like population that is derived ex vivo from cardiac biopsies; they confer both cardioprotection and regeneration in acute myocardial infarction (MI). While the regenerative effects of CDCs in chronic settings have been studied extensively, little is known about how CDCs confer the cardioprotective process known as cellular postconditioning. Here, we used an in vivo rat model of ischemia/reperfusion (IR) injury-induced MI and in vitro coculture assays to investigate how CDCs protect stressed cardiomyocytes. Compared with control animals, animals that received CDCs 20 minutes after IR had reduced infarct size when measured at 48 hours. CDCs modified the myocardial leukocyte population after ischemic injury. Specifically, introduction of CDCs reduced the number of CD68+ macrophages, and these CDCs secreted factors that polarized macrophages toward a distinctive cardioprotective phenotype that was not M1 or M2. Systemic depletion of macrophages with clodronate abolished CDC-mediated cardioprotection. Using both in vitro coculture assays and a rat model of adoptive transfer after IR, we determined that CDC-conditioned macrophages attenuated cardiomyocyte apoptosis and reduced infarct size, thereby recapitulating the beneficial effects of CDC therapy. Together, our data indicate that CDCs limit acute injury by polarizing an effector macrophage population within the heart.

Heart failure causes cholinergic transdifferentiation of cardiac sympathetic nerves via gp130-signaling cytokines in rodents

Although several cytokines and neurotrophic factors induce sympathetic neurons to transdifferentiate into cholinergic neurons in vitro, the physiological and pathophysiological roles of this remain unknown. During congestive heart failure (CHF), sympathetic neural tone is upregulated, but there is a paradoxical reduction in norepinephrine synthesis and reuptake in the cardiac sympathetic nervous system (SNS). Here we examined whether cholinergic transdifferentiation can occur in the cardiac SNS in rodent models of CHF and investigated the underlying molecular mechanism(s) using genetically modified mice. We used Dahl salt-sensitive rats to model CHF and found that, upon CHF induction, the cardiac SNS clearly acquired cholinergic characteristics. Of the various cholinergic differentiation factors, leukemia inhibitory factor (LIF) and cardiotrophin-1 were strongly upregulated in the ventricles of rats with CHF. Further, LIF and cardiotrophin-1 secreted from cultured failing rat cardiomyocytes induced cholinergic transdifferentiation in cultured sympathetic neurons, and this process was reversed by siRNAs targeting Lif and cardiotrophin-1. Consistent with the data in rats, heart-specific overexpression of LIF in mice caused cholinergic transdifferentiation in the cardiac SNS. Further, SNS-specific targeting of the gene encoding the gp130 subunit of the receptor for LIF and cardiotrophin-1 in mice prevented CHF-induced cholinergic transdifferentiation. Cholinergic transdifferentiation was also observed in the cardiac SNS of autopsied patients with CHF. Thus, CHF causes target-dependent cholinergic transdifferentiation of the cardiac SNS via gp130-signaling cytokines secreted from the failing myocardium.

Nerve Growth Factor Is Critical for Cardiac Sensory Innervation and Rescues Neuropathy in Diabetic Hearts

Background— Molecular mechanisms regulating the cardiac sensory nervous system remain poorly understood. Cardiac sensory nerve impairment causes silent myocardial ischemia, a main cause of sudden death in diabetes mellitus (DM). The present study focused on the roles of nerve growth factor (NGF) in the regulation of the cardiac sensory nervous system and analyzed the mechanism of silent myocardial ischemia in DM. Methods and Results— We screened neurotrophic factors and found that cardiac sensory nerves developed in parallel with NGF synthesized in the heart. Cardiac nociceptive sensory nerves that were immunopositive for calcitonin gene-related peptide, dorsal root ganglia (DRG), and the dorsal horn were markedly retarded in NGF-deficient mice, whereas cardiac-specific overexpression of NGF rescued these deficits. DM was induced with streptozotocin in wild-type and transgenic mice overexpressing NGF in the heart. Downregulation of NGF, calcitonin gene-related peptide–immunopositive cardiac sensory denervation, and atrophic changes in DRG were observed in DM-induced wild-type mice, whereas these deteriorations were reversed in DM-induced NGF transgenic mice. Cardiac sensory function, measured by myocardial ischemia–induced c-Fos expression in DRG, was also downregulated by DM in the wild-type mice but not in NGF transgenic mice. Direct gene transfer of NGF in the diabetic rat hearts improved impaired cardiac sensory innervation and function, determined by electrophysiological activity of cardiac afferent nerves during myocardial ischemia. Conclusions— These findings demonstrate that the development and regulation of the cardiac sensory nervous system are dependent on NGF synthesized in the heart and that DM-induced NGF reduction causes cardiac sensory neuropathy.

Cardiac Sympathetic Rejuvenation: A Link Between Nerve Function and Cardiac Hypertrophy

Neuronal function and innervation density is regulated by target organ-derived neurotrophic factors. Although cardiac hypertrophy drastically alternates the expression of various growth factors such as endothelin-1, angiotensin II, and leukemia inhibitory factor, little is known about nerve growth factor expression and its effect on the cardiac sympathetic nerves. This study investigated the impact of pressure overload-induced cardiac hypertrophy on the innervation density and cellular function of cardiac sympathetic nerves, including kinetics of norepinephrine synthesis and reuptake, and neuronal gene expression. Right ventricular hypertrophy was induced by monocrotaline treatment in Wistar rats. Newly developed cardiac sympathetic nerves expressing β3-tubulin (axonal marker), GAP43 (growth-associated cone marker), and tyrosine hydroxylase were markedly increased only in the right ventricle, in parallel with nerve growth factor upregulation. However, norepinephrine and dopamine content was paradoxically attenuated, and the protein and kinase activity of tyrosine hydroxylase were markedly downregulated in the right ventricle. The reuptake of [125I]-metaiodobenzylguanidine and [3H]-norepinephrine were also significantly diminished in the right ventricle, indicating functional downregulation in cardiac sympathetic nerves. Interestingly, we found cardiac sympathetic nerves in hypertrophic right ventricles strongly expressed highly polysialylated neural cell adhesion molecule (PSA-NCAM) (an immature neuron marker) as well as neonatal heart. Taken together, pressure overload induced anatomical sympathetic hyperinnervation but simultaneously caused deterioration of neuronal cellular function. This phenomenon was explained by the rejuvenation of cardiac sympathetic nerves as well as the hypertrophic cardiomyocytes, which also showed the fetal form gene expression.

Cellular Postconditioning Allogeneic Cardiosphere-Derived Cells Reduce Infarct Size and Attenuate Microvascular Obstruction When Administered After Reperfusion in Pigs With Acute Myocardial Infarction

Background—Intracoronary delivery of cardiosphere-derived cells (CDCs) has been demonstrated to be safe and effective in porcine and human chronic myocardial infarction. However, intracoronary delivery of CDCs after reperfusion in acute myocardial infarction has never been assessed in a clinically-relevant large animal model. We tested CDCs as adjunctive therapy to reperfusion in a porcine model of myocardial infarction. Methods and Results—First, escalating doses (5, 7.5, and 10 million cells) of allogeneic CDCs were administered intracoronary 30 minutes after reperfusion. Forty-eight hours later, left ventriculography was performed and animals euthanized to measure area at risk, infarct size (IS), and microvascular obstruction. Second, identical end points were measured in a pivotal study of minipigs (n=14) that received 8.5 to 9 million allogeneic CDCs, placebo solution, or sham. Multiple indicators of cardioprotection were observed with 7.5 and 10 million allogeneic CDCs, but not 5 million CDCs, relative to control. In the pivotal study, IS, microvascular obstruction, cardiomyocyte apoptosis, and adverse left ventricular remodeling were all smaller in the CDC group than in sham or placebo groups. In addition, serum troponin I level at 24 hours was lower after CDC infusion than that in the placebo or sham groups, consistent with the histologically-demonstrated reduction in IS. Conclusions—Intracoronary delivery of allogeneic CDCs is safe, feasible, and effective in cardioprotection, reducing IS, preventing microvascular obstruction, and attenuating adverse acute remodeling. This novel cardioprotective effect, which we call cellular postconditioning, differs from previous strategies to reduce IS in that it works even when initiated with significant delay after reflow.

Norepinephrine-induced nerve growth factor depletion causes cardiac sympathetic denervation in severe heart failure

In severe congestive heart failure (CHF), sympathetic overactivity correlates with the exacerbation of cardiac performance. To test the hypothesis that the cardiac sympathetic nerve density dramatically changes with the acceleration of circulating norepinephrine (NE) concentration, we investigated the temporal association of nerve growth factor (NGF) expression in the heart and cardiac sympathetic nerve density during the development of CHF in the continuous NE-infused rats. The animals were analyzed at 0-, 1-, 3-, 7-, 14-, and 28-day after implantation of osmotic pump at a rate of 0.05 mg/kg/hr. The cardiac performance was temporally facilitated in NE-exposed rats at 3-day in accordance with the sympathetic hyper-innervation induced by the augmentation of NGF mRNA expression in the heart. In NE-treated rats, left ventricular end-diastolic pressure was significantly increased after 7-day and marked left ventricular hypertrophy and systemic fluid retention were observed at 28-day. CHF-induced sympathetic overactivity further increased plasma NE concentration in NE-treated rats and finally reached to 16.1+/-5.6 ng/ml at 28-day (control level was 0.39+/-0.1 ng/ml, p<0.01). In the decompensated CHF rats at 28-day, the NGF mRNA expression was conspicuously reduced concomitant with the obvious nerve fiber loss confirmed by the immunostaining of nerve axonal marker, PGP9.5 and sympathetic neuron marker, tyrosine hydroxylase. This resulted in the attenuated tissue NE contents and the exacerbating cardiac performance. The cardiac sympathetic fiber loss was also confirmed in NE-exposed DBH (dopamine beta-hydroxylase)-Cre/Floxed-EGFP (enhanced green fluorescent protein) mice with severe CHF, in which sympathetic nerve could be traced by EGFP. Our results suggest that the cardiac sympathetic nerve density is strictly regulated by the NGF expression in the heart and long-exposure of high plasma NE concentration caused myocardial NGF reduction, following sympathetic fiber loss in severe CHF animals.

Neural Crest–Derived Stem Cells Migrate and Differentiate Into Cardiomyocytes After Myocardial Infarction

Objective—We recently demonstrated that primitive neural crest–derived (NC) cells migrate from the cardiac neural crest during embryonic development and remain in the heart as dormant stem cells, with the capacity to differentiate into various cell types, including cardiomyocytes. Here, we examined the migration and differentiation potential of these cells on myocardial infarction (MI). Methods and Results—We obtained double-transgenic mice by crossing protein-0 promoter-Cre mice with Floxed–enhanced green fluorescent protein mice, in which the NC cells express enhanced green fluorescent protein. In the neonatal heart, NC stem cells (NCSCs) were localized predominantly in the outflow tract, but they were also distributed in a gradient from base to apex throughout the ventricular myocardium. Time-lapse video analysis revealed that the NCSCs were migratory. Some NCSCs persisted in the adult heart. On MI, NCSCs accumulated at the ischemic border zone area (BZA), which expresses monocyte chemoattractant protein-1 (MCP-1). Ex vivo cell migration assays demonstrated that MCP-1 induced NCSC migration and that this chemotactic effect was significantly depressed by an anti-MCP-1 antibody. Small NC cardiomyocytes first appeared in the BZA 2 weeks post-MI and gradually increased in number thereafter. Conclusion—These results suggested that NCSCs migrate into the BZA via MCP-1/CCR2 signaling and contribute to the provision of cardiomyocytes for cardiac regeneration after MI.

A Massive Suspension Culture System With Metabolic Purification for Human Pluripotent Stem Cell-Derived Cardiomyocytes

Cardiac regenerative therapy with human pluripotent stem cells (hPSCs), such as human embryonic stem cells and induced pluripotent stem cells, has been hampered by the lack of efficient strategies for expanding functional cardiomyocytes (CMs) to clinically relevant numbers. The development of the massive suspension culture system (MSCS) has shed light on this critical issue, although it remains unclear how hPSCs could differentiate into functional CMs using a MSCS. The proliferative rate of differentiating hPSCs in the MSCS was equivalent to that in suspension cultures using nonadherent culture dishes, although the MSCS provided more homogeneous embryoid bodies (EBs), eventually reducing apoptosis. However, pluripotent markers such as Oct3/4 and Tra‐1‐60 were still expressed in EBs 2 weeks after differentiation, even in the MSCS. The remaining undifferentiated stem cells in such cultures could retain a strong potential for teratoma formation, which is the worst scenario for clinical applications of hPSC‐derived CMs. The metabolic purification of CMs in glucose‐depleted and lactate‐enriched medium successfully eliminated the residual undifferentiated stem cells, resulting in a refined hPSC‐derived CM population. In colony formation assays, no Tra‐1‐60‐positive colonies appeared after purification. The nonpurified CMs in the MSCS produced teratomas at a rate of 60%. However, purified CMs never induced teratomas, and enriched CMs showed proper electrophysiological properties and calcium transients. Overall, the combination of a MSCS and metabolic selection is a highly effective and practical approach to purify and enrich massive numbers of functional CMs and provides an essential technique for cardiac regenerative therapy with hPSC‐derived CMs.