Ioan Cucoranu

NAD(P)H Oxidase 4 Mediates Transforming Growth Factor-β1–Induced Differentiation of Cardiac Fibroblasts Into Myofibroblasts

Human cardiac fibroblasts are the main source of cardiac fibrosis associated with cardiac hypertrophy and heart failure. Transforming growth factor-β1 (TGF-β1) irreversibly converts fibroblasts into pathological myofibroblasts, which express smooth muscle α-actin (SM α-actin) de novo and produce extracellular matrix. We hypothesized that TGF-β1–stimulated conversion of fibroblasts to myofibroblasts requires reactive oxygen species derived from NAD(P)H oxidases (Nox). We found that TGF-β1 potently upregulates the contractile marker SM α-actin mRNA (7.5±0.8-fold versus control). To determine whether Nox enzymes are involved, we first performed quantitative real time polymerase chain reaction and found that Nox5 and Nox4 are abundantly expressed in cardiac fibroblasts, whereas Nox1 and Nox2 are barely detectable. On stimulation with TGF-β1, Nox4 mRNA is dramatically upregulated by 16.2±0.8-fold (n=3, P<0.005), whereas Nox5 is downregulated. Small interference RNA against Nox4 downregulates Nox4 mRNA by 80±5%, inhibits NADPH-driven superoxide production in response to TGF-β1 by 65±7%, and reduces TGF-β1–induced expression of SM α-actin by 95±2% (n=6, P<0.05). Because activation of small mothers against decapentaplegic (Smads) 2/3 is critical for myofibroblast conversion in response to TGF-β1, we also determined whether Nox4 affects Smad 2/3 phosphorylation. Depletion of Nox4 but not Nox5 inhibits baseline and TGF-β1 stimulation of Smad 2/3 phosphorylation by 75±5% and 68±3%, respectively (n=7, P<0.0001). We conclude that Nox 4 mediates TGF-β1–induced conversion of fibroblasts to myofibroblasts by regulating Smad 2/3 activation. Thus, Nox4 may play a critical role in the pathological activation of cardiac fibroblasts in cardiac fibrosis associated with human heart failure.

FOXO3A Regulates Peroxiredoxin III Expression in Human Cardiac Fibroblasts

Human cardiac fibroblasts are protected from oxidative stress triggered by inflammation after myocardial injury (Li, P. F., Dietz, R., and von Harsdorf, R. (1999) FEBS Lett. 448, 206–210) by expressing potent antioxidant defenses such as superoxide dismutases, catalases, glutathione-peroxidases, and peroxiredoxins. Recently the transcription factor FOXO3A has been shown to increase resistance to oxidative stress by up-regulation of mitochondrial superoxide dismutase and peroxisomal catalase (Kops, G. J., Dansen, T. B., Polderman, P. E., Saarloos, I., Wirtz, K. W., Coffer, P. J., Huang, T. T., Bos, J. L., Medema, R. H., and Burgering, B. M. (2002) Nature 419, 316–321; Nemoto, S., and Finkel, T. (2002) Science 295, 2450–2452). We hypothesized that FOXO3A also regulates the expression of Prx III, the mitochondrial peroxiredoxin, in human cardiac fibroblasts. We found that depletion of FOXO3A leads to a dramatic reduction of Prx III mRNA and protein in serum-deprived human cardiac fibroblasts. These data suggest that endogenous FOXO3A is necessary for base-line expression of Prx III. Next, we identified two putative FOXO3A DNA binding sites in Prx III promoter at –267 and –244 nucleotides relative to the start codon. We demonstrated that both sequences are required for binding of endogenous FOXO3A to the Prx III promoter by performing electromobility shift assays and chromatin immunoprecipitation assays. Inhibition of endogenous FOXO3A by insulin growth factor 1 prevented binding of FOXO3A to Prx III promoter. In contrast, overexpression of FOXO3A increased Prx III promoter activity. Furthermore, depletion of Prx III was associated with enhanced apoptosis and oxidative stress after serum deprivation. We conclude that FOXO3A mediates Prx III expression, and this may play a critical role in the resistance to oxidative stress in cardiac fibroblasts.

Transgenic mitochondrial superoxide dismutase and mitochondrially targeted catalase prevent antiretroviral-induced oxidative stress and cardiomyopathy

Transgenic mice (TG) were used to define mitochondrial oxidative stress and cardiomyopathy (CM) induced by zidovudine (AZT), an antiretroviral used to treat HIV/AIDS. Genetically engineered mice either depleted or overexpressed mitochondrial superoxide dismutase (SOD2+/− KOs and SOD2-OX, respectively) or expressed mitochondrially targeted catalase (mCAT). TGs and wild-type (WT) littermates were treated (oral AZT, 35 days). Cardiac mitochondrial H2O2, aconitase activity, histology and ultrastructure were analyzed. Left ventricle (LV) mass and LV end-diastolic dimension were determined echocardiographically. AZT induced cardiac oxidative stress and LV dysfunction in WTs. Cardiac mitochondrial H2O2 increased and aconitase was inactivated in SOD2+/− KOs, and cardiac dysfunction was worsened by AZT. Conversely, the cardiac function in SOD2-OX and mCAT hearts was protected. In SOD2-OX and mCAT TG hearts, mitochondrial H2O2, LV mass and LV cavity volume resembled corresponding values from vehicle-treated WTs. AZT worsens cardiac dysfunction and increases mitochondrial H2O2 in SOD2+/− KO. Conversely, both SOD2-OX and mCAT TGs prevent or attenuate AZT-induced cardiac oxidative stress and LV dysfunction. As dysfunctional changes are ameliorated by decreasing and worsened by increasing H2O2 abundance, oxidative stress from H2O2 is crucial pathogenetically in AZT-induced mitochondrial CM.

Murine cardiac mtDNA: effects of transgenic manipulation of nucleoside phosphorylation

Mitochondrial toxicity results from pyrimidine nucleoside reverse transcriptase inhibitors (NRTIs) for HIV/AIDS. In the heart, this can deplete mitochondrial (mt) DNA and cause cardiac dysfunction (eg, left ventricle hypertrophy, LVH). Four unique transgenic, cardiac-targeted overexpressors (TGs) were generated to determine their individual impact on native mitochondrial biogenesis and effects of NRTI administration on development of mitochondrial toxicity. TGs included cardiac-specific overexpression of native thymidine kinase 2 (TK2), two pathogenic TK2 mutants (H121N and I212N), and a mutant of mtDNA polymerase, pol-γ (Y955C). Each was treated with antiretrovirals (AZT-HAART, 3 or 10 weeks, zidovudine (AZT) + lamivudine (3TC) + indinavir, or vehicle control). Parameters included left ventricle (LV) performance (echocardiography), LV mtDNA abundance (real-time PCR), and mitochondrial fine structure (electron microscopy, EM) as a function of duration of treatment and presence of TG. mtDNA abundance significantly decreased in Y955C TG, increased in TK2 native and I212N TGs, and was unchanged in H121N TGs at 10 weeks regardless of treatment. Y955C and I212N TGs exhibited LVH during growth irrespective of treatment. Y955C TGs exhibited cardiomyopathy (CM) at 3 and 10 weeks irrespective of treatment, whereas H121N and I212N TGs exhibited CM only after 10 weeks AZT-HAART. EM features were consistent with cardiac dysfunction. mtDNA abundance and cardiac functional changes were related to TG expression of mitochondrially related genes, mutations thereof, and NRTIs.

Transgenic cardiac-targeted overexpression of human thymidylate kinase

Thymidylate kinase (TMPK) is a nucleoside monophosphate kinase that catalyzes phosphorylation of thymidine monophosphate to thymidine diphosphate. TMPK also mediates phosphorylation of monophosphates of thymidine nucleoside analog (NA) prodrugs on the pathway to their active triphosphate antiviral or antitumor moieties. Novel transgenic mice (TG) expressing human (h) TMPK were genetically engineered using the α-myosin heavy chain promoter to drive its cardiac-targeted overexpression. In ‘2 by 2’ protocols, TMPK TGs and wild-type (WT) littermates were treated with the NA zidovudine (a deoxythymidine analog, 3′-azido-3′deoxythymidine (AZT)) or vehicle for 35 days. Alternatively, TGs and WTs were treated with a deoxycytidine NA (racivir, RCV) or vehicle. Changes in mitochondrial DNA (mtDNA) abundance and mitochondrial ultrastructure were defined quantitatively by real-time PCR and transmission electron microscopy, respectively. Cardiac performance was determined echocardiographically. Results showed TMPK TGs treated with either AZT or RCV exhibited decreased cardiac mtDNA abundance. Cardiac ultrastructural changes were seen only with AZT. AZT-treated TGs exhibited increased left ventricle (LV) mass. In contrast, LV mass in RCV-treated TGs and WTs remained unchanged. In all cohorts, LV end-diastolic dimension remained unchanged. This novel cardiac-targeted overexpression of hTMPK helps define the role of TMPK in mitochondrial toxicity of antiretrovirals.