Yoshinori Katsumata

Induction of Cardiomyocyte-Like Cells in Infarct Hearts by Gene Transfer of Gata4, Mef2c, and Tbx5

Rationale: After myocardial infarction (MI), massive cell death in the myocardium initiates fibrosis and scar formation, leading to heart failure. We recently found that a combination of 3 cardiac transcription factors, Gata4, Mef2c, and Tbx5 (GMT), reprograms fibroblasts directly into functional cardiomyocytes in vitro. Objective: To investigate whether viral gene transfer of GMT into infarcted hearts induces cardiomyocyte generation. Methods and Results: Coronary artery ligation was used to generate MI in the mouse. In vitro transduction of GMT retrovirus converted cardiac fibroblasts from the infarct region into cardiomyocyte-like cells with cardiac-specific gene expression and sarcomeric structures. Injection of the green fluorescent protein (GFP) retrovirus into mouse hearts, immediately after MI, infected only proliferating noncardiomyocytes, mainly fibroblasts, in the infarct region. The GFP expression diminished after 2 weeks in immunocompetent mice but remained stable for 3 months in immunosuppressed mice, in which cardiac induction did not occur. In contrast, injection of GMT retrovirus into &agr;-myosin heavy chain (&agr;MHC)-GFP transgenic mouse hearts induced the expression of &agr;MHC-GFP, a marker of cardiomyocytes, in 3% of virus-infected cells after 1 week. A pooled GMT injection into the immunosuppressed mouse hearts induced cardiac marker expression in retrovirus-infected cells within 2 weeks, although few cells showed striated muscle structures. To transduce GMT efficiently in vivo, we generated a polycistronic retrovirus expressing GMT separated by 2A “self-cleaving” peptides (3F2A). The 3F2A-induced cardiomyocyte-like cells in fibrotic tissue expressed sarcomeric &agr;-actinin and cardiac troponin T and had clear cross striations. Quantitative RT-PCR also demonstrated that FACS-sorted 3F2A-transduced cells expressed cardiac-specific genes. Conclusions: GMT gene transfer induced cardiomyocyte-like cells in infarcted hearts.

Temporal dynamics of cardiac immune cell accumulation following acute myocardial infarction

Acute myocardial infarction (MI) causes sterile inflammation, which is characterized by recruitment and activation of innate and adaptive immune system cells. Here we delineate the temporal dynamics of immune cell accumulation following MI by flow cytometry. Neutrophils increased immediately to a peak at 3 days post-MI. Macrophages were numerically the predominant cells infiltrating the infarcted myocardium, increasing in number over the first week post-MI. Macrophages are functionally heterogeneous, whereby the first responders exhibit high expression levels of proinflammatory mediators, while the late responders express high levels of the anti-inflammatory cytokine IL-10; these macrophages can be classified into M1 and M2 macrophages, respectively, based on surface-marker expression. M1 macrophages dominated at 1-3 days post-MI, whereas M2 macrophages represented the predominant macrophage subset after 5 days. The M2 macrophages expressed high levels of reparative genes in addition to proinflammatory genes to the same levels as in M1 macrophages. The predominant subset of dendritic cells (DCs) was myeloid DC, which peaked in number on day 7. Th1 and regulatory T cells were the predominant subsets of CD4(+) T cells, whereas Th2 and Th17 cells were minor populations. CD8(+) T cells, γδT cells, B cells, natural killer (NK) cells and NKT cells peaked on day 7 post-MI. Timely reperfusion reduced the total number of leukocytes accumulated in the post-MI period, shifting the peak of innate immune response towards earlier and blunting the wave of adaptive immune response. In conclusion, these results provide important knowledge necessary for developing successful immunomodulatory therapies.

Metabolic Remodeling Induced by Mitochondrial Aldehyde Stress Stimulates Tolerance to Oxidative Stress in the Heart

Rationale: Aldehyde accumulation is regarded as a pathognomonic feature of oxidative stress–associated cardiovascular disease. Objective: We investigated how the heart compensates for the accelerated accumulation of aldehydes. Methods and Results: Aldehyde dehydrogenase 2 (ALDH2) has a major role in aldehyde detoxification in the mitochondria, a major source of aldehydes. Transgenic (Tg) mice carrying an Aldh2 gene with a single nucleotide polymorphism (Aldh2*2) were developed. This polymorphism has a dominant-negative effect and the Tg mice exhibited impaired ALDH activity against a broad range of aldehydes. Despite a shift toward the oxidative state in mitochondrial matrices, Aldh2*2 Tg hearts displayed normal left ventricular function by echocardiography and, because of metabolic remodeling, an unexpected tolerance to oxidative stress induced by ischemia/reperfusion injury. Mitochondrial aldehyde stress stimulated eukaryotic translation initiation factor 2&agr; phosphorylation. Subsequent translational and transcriptional activation of activating transcription factor-4 promoted the expression of enzymes involved in amino acid biosynthesis and transport, ultimately providing precursor amino acids for glutathione biosynthesis. Intracellular glutathione levels were increased 1.37-fold in Aldh2*2 Tg hearts compared with wild-type controls. Heterozygous knockout of Atf4 blunted the increase in intracellular glutathione levels in Aldh2*2 Tg hearts, thereby attenuating the oxidative stress–resistant phenotype. Furthermore, glycolysis and NADPH generation via the pentose phosphate pathway were activated in Aldh2*2 Tg hearts. (NADPH is required for the recycling of oxidized glutathione.) Conclusions: The findings of the present study indicate that mitochondrial aldehyde stress in the heart induces metabolic remodeling, leading to activation of the glutathione–redox cycle, which confers resistance against acute oxidative stress induced by ischemia/reperfusion.

4-hydroxy-2-nonenal protects against cardiac ischemia-reperfusion injury via the Nrf2-dependent pathway.

Reactive oxygen species (ROS) attack polyunsaturated fatty acids of the membrane and trigger lipid peroxidation, which results in the generation of alpha,beta-unsaturated aldehydes, such as 4-hydroxy-2-nonenal (4-HNE). There is compelling evidence that high concentrations of aldehydes are responsible for much of the damage elicited by cardiac ischemia-reperfusion injury, while sublethal concentrations of aldehydes stimulate stress resistance pathways, to achieve cardioprotection. We investigated the mechanism of cardioprotection mediated by 4-HNE. For cultured cardiomyocytes, 4-HNE was cytotoxic at higher concentrations (>or=20 microM) but had no appreciable cytotoxicity at lower concentrations. Notably, a sublethal concentration (5muM) of 4-HNE primed cardiomyocytes to become resistant to cytotoxic concentrations of 4-HNE. 4-HNE induced nuclear translocation of transcription factor NF-E2-related factor 2 (Nrf2), and enhanced the expression of gamma-glutamylcysteine ligase (GCL) and the core subunit of the Xc(-) high-affinity cystine transporter (xCT), thereby increasing 1.45-fold the intracellular GSH levels. Cardiomyocytes treated with either Nrf2-specific siRNA or the GCL inhibitor l-buthionine sulfoximine (BSO) were less tolerant to 4-HNE. Moreover, the cardioprotective effect of 4-HNE pretreatment against subsequent glucose-free anoxia followed by reoxygenation was completely abolished in these cells. Intravenous administration of 4-HNE (4 mg/kg) activated Nrf2 in the heart and increased the intramyocardial GSH content, and consequently improved the functional recovery of the left ventricle following ischemia-reperfusion in Langendorff-perfused hearts. This cardioprotective effect of 4-HNE was not observed for Nrf2-knockout mice. In summary, 4-HNE activates Nrf2-mediated gene expression and stimulates GSH biosynthesis, thereby conferring on cardiomyocytes protection against ischemia-reperfusion injury.

Caloric Restriction Primes Mitochondria for Ischemic Stress by Deacetylating Specific Mitochondrial Proteins of the Electron Transport Chain

Rationale: Caloric restriction (CR) confers cardioprotection against ischemia/reperfusion injury. However, the exact mechanism(s) underlying CR-induced cardioprotection remain(s) unknown. Recent evidence indicates that Sirtuins, NAD+-dependent deacetylases, regulate various favorable aspects of the CR response. Thus, we hypothesized that deacetylation of specific mitochondrial proteins during CR preserves mitochondrial function and attenuates production of reactive oxygen species during ischemia/reperfusion. Objective: The objectives of the present study were (1) to investigate the effect of CR on mitochondrial function and mitochondrial proteome and (2) to investigate what molecular mechanisms mediate CR-induced cardioprotection. Methods and Results: Male 26-week-old Fischer344 rats were randomly divided into ad libitum–fed and CR (40% reduction) groups for 6 months. No change was observed in basal mitochondrial function, but CR preserved postischemic mitochondrial respiration and attenuated postischemic mitochondrial H2O2 production. CR decreased the level of acetylated mitochondrial proteins that were associated with enhanced Sirtuin activity in the mitochondrial fraction. We confirmed a significant decrease in the acetylated forms of NDUFS1 and cytochrome bc1 complex Rieske subunit in the CR heart. Low-dose Resveratrol treatment mimicked the effect of CR on deacetylating them and attenuated reactive oxygen species production during anoxia/reoxygenation in cultured cardiomyocytes without changing the expression levels of manganese superoxide dismutase. Treatment with nicotinamide completely abrogated the effect of low-dose Resveratrol. Conclusions: These results strongly suggest that CR primes mitochondria for stress resistance by deacetylating specific mitochondrial proteins of the electron transport chain. Targeted deacetylation of NDUFS1 and/or Rieske subunit might have potential as a novel therapeutic approach for cardioprotection against ischemia/reperfusion.

Deleterious Effect of the IL-23/IL-17A Axis and γδT Cells on Left Ventricular Remodeling After Myocardial Infarction

Background Left ventricular (LV) remodeling leads to chronic heart failure and is a main determinant of morbidity and mortality after myocardial infarction (MI). At the present time, therapeutic options to prevent LV remodeling are limited. Methods and Results We created a large MI by permanent ligation of the coronary artery and identified a potential link between the interleukin (IL)–23/IL-17A axis and γδT cells that affects late-stage LV remodeling after MI. Despite the finsinf that infarct size 24 hours after surgery was similar to that in wild-type mice, a deficiency in IL-23, IL-17A, or γδT cells improved survival after 7 days, limiting infarct expansion and fibrosis in noninfarcted myocardium and alleviating LV dilatation and systolic dysfunction on day 28 post-MI. M1 macrophages and neutrophils were the major cellular source of IL-23, whereas >90% of IL-17A-producing T cells in infarcted heart were CD4− TCRγδ+ (γδT) cells. Toll-like receptor signaling and IL-1β worked in concert with IL-23 to drive expansion and IL-17A production in cardiac γδT cells, whereas the sphingosine-1-phosphate receptor and CCL20/CCR6 signaling pathways mediated γδT cell recruitment into infarcted heart. IL-17A was not involved in the acute inflammatory response, but it functioned specifically in the late remodeling stages by promoting sustained infiltration of neutrophils and macrophages, stimulating macrophages to produce proinflammatory cytokines, aggravating cardiomyocyte death, and enhancing fibroblast proliferation and profibrotic gene expression. Conclusions The IL-23/IL-17A immune axis and γδT cells are potentially promising therapeutic targets after MI to prevent progression to end-stage dilated cardiomyopathy.

Obesity accelerates T cell senescence in murine visceral adipose tissue

Chronic inflammation in visceral adipose tissue (VAT) precipitates the development of cardiometabolic disorders. Although changes in T cell function associated with visceral obesity are thought to affect chronic VAT inflammation, the specific features of these changes remain elusive. Here, we have determined that a high-fat diet (HFD) caused a preferential increase and accumulation of CD44hiCD62LloCD4+ T cells that constitutively express PD-1 and CD153 in a B cell-dependent manner in VAT. These cells possessed characteristics of cellular senescence and showed a strong activation of Spp1 (encoding osteopontin [OPN]) in VAT. Upon T cell receptor stimulation, these T cells also produced large amounts of OPN in a PD-1-resistant manner in vitro. The features of CD153+PD-1+CD44hiCD4+ T cells were highly reminiscent of senescence-associated CD4+ T cells that normally increase with age. Adoptive transfer of CD153+PD-1+CD44hiCD4+ T cells from HFD-fed WT, but not Spp1-deficient, mice into the VAT of lean mice fed a normal diet recapitulated the essential features of VAT inflammation and insulin resistance. Our results demonstrate that a distinct CD153+PD-1+CD44hiCD4+ T cell population that accumulates in the VAT of HFD-fed obese mice causes VAT inflammation by producing large amounts of OPN. This finding suggests a link between visceral adiposity and immune aging.

Adventitial CXCL1/G-CSF expression in response to acute aortic dissection triggers local neutrophil recruitment and activation leading to aortic rupture

Rationale: In-hospital outcomes are generally acceptable in patients with type B dissection; however, some patients present with undesirable complications, such as aortic expansion and rupture. Excessive inflammation is an independent predictor of adverse clinical outcomes. Objective: We have investigated the underlying mechanisms of catastrophic complications after acute aortic dissection (AAD) in mice. Methods and Results: When angiotensin II was administered in lysyl oxidase inhibitor–preconditioned mice, AAD emerged within 24 hours. The dissection was initiated at the proximal site of the descending thoracic aorta and propagated distally into an abdominal site. Dissection of the aorta caused dilatation, and ≈70% of the mice died of aortic rupture. AAD triggered CXCL1 and granulocyte-colony stimulating factor expression in the tunica adventitia of the dissected aorta, leading to elevation of circulating CXCL1/granulocyte-colony stimulating factor levels. Bone marrow CXCL12 was reduced. These chemokine changes facilitated neutrophil egress from bone marrow and infiltration into the aortic adventitia. Interference of CXCL1 function using an anti-CXCR2 antibody reduced neutrophil accumulation and limited aortic rupture post AAD. The tunica adventitia of the expanded dissected aorta demonstrated high levels of interleukin-6 (IL-6) expression. Neutrophils were the major sources of IL-6, and CXCR2 neutralization significantly reduced local and systemic levels of IL-6. Furthermore, disruption of IL-6 effectively suppressed dilatation and rupture of the dissected aorta without any influence on the incidence of AAD and neutrophil mobilization. Conclusions: Adventitial CXCL1/granulocyte-colony stimulating factor expression in response to AAD triggers local neutrophil recruitment and activation. This leads to adventitial inflammation via IL-6 and results in aortic expansion and rupture.

Endogenous Prostaglandin D2 and Its Metabolites Protect the Heart Against Ischemia–Reperfusion Injury by Activating Nrf2

We recently demonstrated that glucocorticoids markedly upregulate the expression of cyclooxygenase-2 in cardiomyocytes and protect hearts from ischemia–reperfusion (I/R) injury by activating lipocalin-type prostaglandin D (PGD) synthase (L-PGDS)–derived PGD2 biosynthesis. We examined a downstream mechanism of cardioprotection elicited by PGD2 biosynthesis. Acute PGD2 treatment did not protect hearts against I/R injury. We then speculated that PGD2 and its metabolite 15-deoxy-&Dgr;12,14-PGJ2 activate gene expression networks to mediate the glucocorticoid-mediated cardioprotection. Using an unbiased approach, we identified that glucocorticoids induce a number of well-known erythroid-derived 2–like 2 (Nrf2) target genes in the heart in an L-PGDS–dependent manner and that the cardioprotective effect of glucocorticoids against I/R injury was not seen in Nrf2-knockout hearts. We showed relatively low expression of PGD2 receptors (ie, DP1 and DP2) in the heart but abundant expression of PGF2&agr; receptor (FP), which binds PGF2&agr; and PGD2 with equal affinity. Glucocorticoids also failed to induce the expression of L-PGDS–dependent Nrf2 target genes in FP-knockout hearts. PGD2 acted through its metabolite 15-deoxy-&Dgr;12,14-PGJ2 in the heart as evidenced by the glucocorticoid-mediated activation of peroxisome proliferator-activated receptor-&ggr;. In turn, glucocorticoids failed to induce the expression of L-PGDS–dependent Nrf2 target genes in hearts pretreated with peroxisome proliferator-activated receptor-&ggr; antagonist GW9662, and glucocorticoid-mediated cardioprotection against I/R injury was compromised in FP-knockout mice and GW9662-treated mice. In conclusion, PGD2 protects heart against I/R injury by activating Nrf2 predominantly via FP receptor. In addition, we propose activation of peroxisome proliferator-activated receptor-&ggr; by the dehydrated metabolite of PGD2 (15-deoxy-&Dgr;12,14-PGJ2) as another mechanism by which glucocorticoids induce cardioprotection.

PGD2-CRTH2 Pathway Promotes Tubulointerstitial Fibrosis

Urinary excretion of lipocalin-type PGD(2) synthase (L-PGDS), which converts PG H(2) to PGD(2), increases in early diabetic nephropathy. In addition, L-PGDS expression in the tubular epithelium increases in adriamycin-induced nephropathy, suggesting that locally produced L-PGDS may promote the development of CKD. In this study, we found that L-PGDS-derived PGD(2) contributes to the progression of renal fibrosis via CRTH2-mediated activation of Th2 lymphocytes. In a mouse model, the tubular epithelium synthesized L-PGDS de novo after unilateral ureteral obstruction (UUO). L-PGDS-knockout mice and CRTH2-knockout mice both exhibited less renal fibrosis, reduced infiltration of Th2 lymphocytes into the cortex, and decreased production of the Th2 cytokines IL-4 and IL-13. Furthermore, oral administration of a CRTH2 antagonist, beginning 3 days after UUO, suppressed the progression of renal fibrosis. Ablation of IL-4 and IL-13 also ameliorated renal fibrosis in the UUO kidney. Taken together, these data suggest that blocking the activation of CRTH2 by PGD(2) might be a strategy to slow the progression of renal fibrosis in CKD.