Cardiac-specific Factors Research Articles

Heart-derived factors and organ cross-talk in settings of health and disease: new knowledge and clinical opportunities for multimorbidity.

Cardiovascular disease affects millions of people worldwide and often presents with other conditions including metabolic, renal and neurological disorders. A variety of secreted factors from multiple organs/tissues (proteins, nucleic acids and lipids) have been implicated in facilitating organ cross-talk that may contribute to the development of multimorbidity. Secreted proteins have received the most attention, with the greatest body of research related to factors released from adipose tissue (adipokines), followed by skeletal muscle (myokines). To date, there have been fewer studies on proteins released from the heart (cardiokines) implicated with organ cross-talk. Early evidence for the secretion of cardiac-specific factors facilitating organ cross-talk came in the form of natriuretic peptides which are secreted via the classical endoplasmic reticulum-Golgi pathway. More recently, studies in cardiomyocyte-specific genetic mouse models have revealed cardiac-initiated organ cross-talk. Cardiomyocyte-specific modulation of microRNAs (miR-208a and miR-23-27-24 cluster) and proteins such as the mediator complex subunit 13 (MED13), G-protein-coupled receptor kinase 2 (GRK2), mutant α-myosin heavy-chain (αMHC), ubiquitin-like modifier-activating enzyme (ATG7), oestrogen receptor alpha (ERα) and fibroblast growth factor 21 (FGF21) have resulted in metabolic and renal phenotypes. These studies have implicated a variety of factors which can be secreted via the classical pathway or via non-classical mechanisms including the release of extracellular vesicles. Cross-talk between the heart and the brain has also been described (e.g. via miR-1 and an emerging concept, interoception: detection of internal neural signals). Here we summarize these studies taking into consideration that factors may be secreted in both settings of health and in disease.

Abstract P1138: Combination Of Pluripotency And Cardiac Transcription Factors Reprogram Skin Fibroblasts Into Cardiomyocytes

Direct reprogramming of autologous somatic cells into cardiomyocytes is a novel approach which is being employed for cardiac regeneration. Multiple studies have combined different cardiac-specific factors that could directly reprogram cardiac fibroblasts into induced cardiomyocyte-like cells. However, this approach needs heart biopsy for the isolation of autologous fibroblasts which involves extensive surgical procedures that require precision. In this study, we aimed to develop an approach which can directly reprogram somatic cells into cardiomyocyte-like cells using a combination of pluripotency and cardiac transcription factors. Skin fibroblasts were isolated from rat neonatal pups and were induced into cardiomyocyte-like cells using non-viral integration of cardiac transcription factors (GATA4, Mef2c and Nkx2.5) and OKSIM plasmid carrying the iPSC factors, Sox2, Oct4, Klf4 and cMyc. After 72 h, cells were analyzed for the expression of cardiac markers by qPCR and immunocytochemistry. Gene expression analysis showed significantly higher expression of cardiac markers GATA4, cMHC, Mef2c, cTnT, cTnI, and Nkx2.5 Immunostaining confirmed the expression of cardiac proteins GATA4, cMHC, cTnT, cTnI, and Nkx2.5. These results imply that the transfected cells started differentiating towards cardiac lineage. Transfected cells were also transplanted in rat myocardial infarction (MI) model immediately after ligation of left ventricle descending (LAD) artery. After 2 and 4 weeks of cell transplantation, the animals were assessed for cardiac function via echocardiography. They showed significant improvement in the cardiac function as compared to MI and non-transfected groups. After 4 weeks, the hearts were harvested, and histological analysis was performed for the assessment of fibrosis and left ventricular wall thickness. Rats transplanted with transfected cells showed significantly reduced fibrosis and increased wall thickness as compared to MI and non-transfected groups. In conclusion, transient and combined expression of cardiac transcription and iPSC factors in neonatal somatic cells leads to the transdifferentiation of skin cells into myogenic lineage. This approach can be useful for future therapeutic application for cardiovascular diseases.

High Fat Programming and Cardiovascular Disease.

Programming is triggered through events during critical developmental phases that alter offspring health outcomes. High fat programming is defined as the maintenance on a high fat diet during fetal and/or early postnatal life that induces metabolic and physiological alterations that compromise health. The maternal nutritional status, including the dietary fatty acid composition, during gestation and/or lactation, are key determinants of fetal and postnatal development. A maternal high fat diet and obesity during gestation compromises the maternal metabolic state and, through high fat programming, presents an unfavorable intrauterine milieu for fetal growth and development thereby conferring adverse cardiac outcomes to offspring. Stressors on the heart, such as a maternal high fat diet and obesity, alter the expression of cardiac-specific factors that alter cardiac structure and function. The proper nutritional balance, including the fatty acid balance, particularly during developmental windows, are critical for maintaining cardiac structure, preserving cardiac function and enhancing the cardiac response to metabolic challenges.

Cardiac-Specific Conversion Factors to Estimate Radiation Effective Dose From Dose-Length Product in Computed Tomography

ObjectivesThis study sought to determine updated conversion factors (k-factors) that would enable accurate estimation of radiation effective dose (ED) for coronary computed tomography angiography (CTA) and calcium scoring performed on 12 contemporary scanner models and current clinical cardiac protocols and to compare these methods to the standard chest k-factor of 0.014 mSv·mGy−1cm−1. BackgroundAccurate estimation of ED from cardiac CT scans is essential to meaningfully compare the benefits and risks of different cardiac imaging strategies and optimize test and protocol selection. Presently, ED from cardiac CT is generally estimated by multiplying a scanner-reported parameter, the dose-length product, by a k-factor which was determined for noncardiac chest CT, using single-slice scanners and a superseded definition of ED. MethodsMetal-oxide-semiconductor field-effect transistor radiation detectors were positioned in organs of anthropomorphic phantoms, which were scanned using all cardiac protocols, 120 clinical protocols in total, on 12 CT scanners representing the spectrum of scanners from 5 manufacturers (GE, Hitachi, Philips, Siemens, Toshiba). Organ doses were determined for each protocol, and ED was calculated as defined in International Commission on Radiological Protection Publication 103. Effective doses and scanner-reported dose-length products were used to determine k-factors for each scanner model and protocol. Resultsk-Factors averaged 0.026 mSv·mGy−1cm−1 (95% confidence interval: 0.0258 to 0.0266) and ranged between 0.020 and 0.035 mSv·mGy−1cm−1. The standard chest k-factor underestimates ED by an average of 46%, ranging from 30% to 60%, depending on scanner, mode, and tube potential. Factors were higher for prospective axial versus retrospective helical scan modes, calcium scoring versus coronary CTA, and higher (100 to 120 kV) versus lower (80 kV) tube potential and varied among scanner models (range of average k-factors: 0.0229 to 0.0277 mSv·mGy−1cm−1). ConclusionsCardiac k-factors for all scanners and protocols are considerably higher than the k-factor currently used to estimate ED of cardiac CT studies, suggesting that radiation doses from cardiac CT have been significantly and systematically underestimated. Using cardiac-specific factors can more accurately inform the benefit-risk calculus of cardiac-imaging strategies.

Global transcriptomic analysis of induced cardiomyocytes predicts novel regulators for direct cardiac reprogramming.

Heart diseases are the most significant cause of morbidity and mortality in the world. De novo generated cardiomyocytes (CMs) are a great cellular source for cell-based therapy and other potential applications. Direct cardiac reprogramming is the newest method to produce CMs, known as induced cardiomyocytes (iCMs). During a direct cardiac reprogramming, also known as transdifferentiation, non-cardiac differentiated adult cells are reprogrammed to cardiac identity by forced expression of cardiac-specific transcription factors (TFs) or microRNAs. To this end, many different combinations of TFs (±microRNAs) have been reported for direct reprogramming of mouse or human fibroblasts to iCMs, although their efficiencies remain very low. It seems that the investigated TFs and microRNAs are not sufficient for efficient direct cardiac reprogramming and other cardiac specific factors may be required for increasing iCM production efficiency, as well as the quality of iCMs. Here, we analyzed gene expression data of cardiac fibroblast (CFs), iCMs and adult cardiomyocytes (aCMs). The up-regulated and down-regulated genes in CMs (aCMs and iCMs) were determined as CM and CF specific genes, respectively. Among CM specific genes, we found 153 transcriptional activators including some cardiac and non-cardiac TFs that potentially activate the expression of CM specific genes. We also identified that 85 protein kinases such as protein kinase D1 (PKD1), protein kinase A (PRKA), calcium/calmodulin-dependent protein kinase (CAMK), protein kinase C (PRKC), and insulin like growth factor 1 receptor (IGF1R) that are strongly involved in establishing CM identity. CM gene regulatory network constructed using protein kinases, transcriptional activators and intermediate proteins predicted some new transcriptional activators such as myocyte enhancer factor 2A (MEF2A) and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PPARGC1A), which may be required for qualitatively and quantitatively efficient direct cardiac reprogramming. Taken together, this study provides new insights into the complexity of cell fate conversion and better understanding of the roles of transcriptional activators, signaling pathways and protein kinases in increasing the efficiency of direct cardiac reprogramming and maturity of iCMs.

SERUM FREE LIGHT CHAIN DIFFERENCE AND MARKERS OF HEART FAILURE SEVERITY ARE CORRELATED WITH ONE YEAR MORTALITY, VENTRICULAR ASSIST DEVICE IMPLANTATION OR HEART TRANSPLANTATION IN NEWLY DIAGNOSED PATIENTS WITH CARDIAC LIGHT CHAIN AMYLOIDOSIS

Serum free light chain difference (FLC-diff) and cardiac specific factors are validated diagnostic and prognostic tools in evaluating prognosis in patients with amyloidosis. However, their utility in those newly diagnosed with cardiac light chain (AL) amyloidosis has not yet been tested. We

Potentiation of Tbx5-mediated transactivation by SUMO conjugation and protein inhibitor of activated STAT 1 (PIAS1)

The role of the T-box transcription factor Tbx5 in heart and limb development has been well documented; however, how posttranslational modification is involved in mediating its activity is unknown. Here we report that Tbx5 is a novel target by SUMO conjugation, a posttranslational modification that is involved in a variety of cellular events. Sumoylation potentiated the transcriptional activity of Tbx5, and PIAS family members, a group of SUMO E3 ligase, differentially mediated sumoylation and function of Tbx5. PIAS1 potently stimulated SUMO conjugation to Tbx5, and the physical association of Tbx5 with PIAS1 was required for its full sumoylation. PIAS1 also enhanced the functional cooperation between Tbx5 and its interaction partners. Overlapping expression pattern and colocalization of PIAS1 and Tbx5 in the mouse embryonic hearts and on the native target gene promoter were observed, pointing to a potential functional interaction of these two factors in vivo. These findings provide novel insights into how the transcriptional activity of a cardiac-specific factor, Tbx5, is regulated both directly and indirectly via posttranslational modification by a non-tissue-specific factor, PIAS1.

Lrrc10 is a novel cardiac-specific target gene of Nkx2-5 and GATA4

Cardiac gene expression is precisely regulated and its perturbation causes developmental defects and heart disease. Leucine-rich repeat containing 10 (Lrrc10) is a cardiac-specific factor that is crucial for proper cardiac development and deletion of Lrrc10 in mice results in dilated cardiomyopathy. However, the mechanisms regulating Lrrc10 expression in cardiomyocytes remain unknown. Therefore, we set out to determine trans-acting factors and cis-elements critical for mediating Lrrc10 expression. We identify Lrrc10 as a transcriptional target of Nkx2-5 and GATA4. The Lrrc10 promoter region contains two highly conserved cardiac regulatory elements, which are functional in cardiomyocytes but not in fibroblasts. In vivo, Nkx2-5 and GATA4 endogenously occupy the proximal and distal cardiac regulatory elements of Lrrc10 in the heart. Moreover, embryonic hearts of Nkx2-5 knockout mice have dramatically reduced expression of Lrrc10. These data demonstrate the importance of Nkx2-5 and GATA4 in regulation of Lrrc10 expression in vivo. The proximal cardiac regulatory element located at around −200bp is synergistically activated by Nkx2-5 and GATA4 while the distal cardiac regulatory element present around −3kb requires SRF in addition to Nkx2-5 and GATA4 for synergistic activation. Mutational analyses identify a pair of adjacent Nkx2-5 and GATA binding sites within the proximal cardiac regulatory element that are necessary to induce expression of Lrrc10. In contrast, only the GATA site is functional in the distal regulatory element. Taken together, our data demonstrate that the transcription factors Nkx2-5 and GATA4 cooperatively regulate cardiac-specific expression of Lrrc10.

Abstract 9724: The Use of the Model for End-Stage Liver Disease Score Predicts 90-Day Mortality in Patients Undergoing HeartMate II Implantation

Purpose: Careful patient selection for left ventricular assist device (LVAD) therapy is essential to ensure optimal outcomes after device implantation. Although several risk assessment scores are available, there is no consensus on the most accurate score to use in patients undergoing HeartMate II (HMII) implantation. The Lietz-Miller Destination Therapy Risk Score (DTRS) was derived from analysis of patients undergoing HeartMate XVE implantation for destination therapy (Lietz et al. Circulation 2007). The Model for End-Stage Liver Disease (MELD) was shown to predict outcome in patients undergoing primarily HeartMate I implantation (Matthews et al. Circulation 2010). We evaluated the utility of these scores in predicting outcomes following HMII implantation. Methods: Retrospective analysis was performed on 48 patients undergoing HMII implantation at our institution between 2009 and 2011. The DTRS and MELD scores were calculated from clinical data on day of device implantation and outcomes assessed. Results: Device implantation was for bridge to transplant (69%) or destination therapy (31%). 14 patients (29%) underwent heart transplant and 17 patients died (35%), with a mean LVAD support time of 301 days and 85 days, respectively. At end of the study period 17 patients were alive (mean LVAD support time 389 days). The majority of deaths (71%) occurred within 90 days of device implantation. Mortality at 90 days was higher in patients with INTERMACS class 1 (class 1 29.4% vs. class 2 to 4 22.6%), high-risk DTRS values (high 33.3% vs. low-medium 22.2%), and high MELD values (MELD 20 50% vs. MELD < 20 16.6%). Only a MELD score 20 was statistically associated with outcome at 90 days with a hazard ratio of 3.5 (p=0.03) using a Cox proportional hazards model. Conclusions: A MELD score 20 predicts mortality at 90 days in patients undergoing HMII implantation. Further validation of the MELD score in a larger population is needed. Elaboration of the score using cardiac-specific factors may further improve its predictive ability.

Abstract 19382: Ablation of the Cardiac-Specific Gene Leucine-Rich Containing 10 (lrrc10) Results in Dilated Cariomyopathy

Dilated cardiomyopathy is the most common form of cardiomyopathy and is a leading cause of heart failure. Leucine-rich repeat containing 10 (LRRC10) is a cardiac-specific protein containing leucine-rich repeat motifs ideal for protein:protein interactions. We have previously shown that LRRC10 is essential for proper cardiac function in developing zebrafish. However, the role of LRRC10 in mammalian cardiac physiology remains unknown. To determine if LRRC10 is critical for mammalian cardiac function, Lrrc10-null (Lrrc10-/-) mice were evaluated by echocardiography. Lrrc10-/- mice exhibit prenatal systolic dysfunction and progressive dilated cardiomyopathy in postnatal life. Importantly, Lrrc10-/- mice have diminished cardiac performance in utero, prior to ventricular dilation observed in young adults. Gene expression profiling revealed that cardiac muscle contraction and oxidative phosphorylation are the most upregulated pathways in adult Lrrc10-/- hearts. We demonstrate that LRRC10 physically interacts with α-actinin and actin isoforms by coimmunoprecipitation, GST pulldown, and yeast two-hybrid screening, suggesting that LRRC10 may provide a link between the myofilament Z-disc and the actin cytoskeleton. Interaction of LRRC10 with α-actinin and actin positions it in ideal location in the cardiomyocyte to sense or transduce signals in response to biomechanical stress. To test the role of LRRC10 in response to biomechanical stress, transverse aortic constriction (TAC) was performed. Lrrc10-/- mice exhibit exacerbated and accelerated cardiomyopathy in response to 28 days of TAC with markedly greater left ventricular (LV) chamber dilation and severely compromised systolic and diastolic function relative to controls. Moreover, endogenous Lrrc10 expression is downregulated in controls in response to TAC, suggesting an important role for LRRC10 in cardiac adaptation to biomechanical stress. In summary, we identify the cardiac-specific factor Lrrc10 as a novel dilated cardiomyopathy candidate gene. LRRC10 is essential for normal cardiac function and is indispensible for proper adaptation of the mammalian heart to biomechanical stress.

S134 High prevalence of ischaemic heart disease (IHD) in patients meeting clinico-radiological profile for idiopathic pulmonary fibrosis (IPF)

IntroductionIPF and ischaemic cardiac disease may share pathological similarities including aberrant tissue remodelling. Given their recognised heterogeneity, we hypothesised that patterns of IPF (usual interstitial pneumonia, UIP; non-specific interstitial pneumonia,...

Identification, Isolation and Characterization of HCN4-Positive Pacemaking Cells Derived from Murine Embryonic Stem Cells during Cardiac Differentiation

Development of biological pacemaker is a potential treatment for bradyarrhythmias. Pacemaker cells could be extracted from differentiated embryonic stem (ES) cells based on their specific cell marker hyperpolarization-activated cyclic nucleotide-gated (HCN)4. The goal of this study was to develop a method of identification, isolation, and characterization of pacemaking cells derived from differentiated ES cells with GFP driven by HCN4 promoter. Polymerase chain reaction (PCR) screening and southern blot analysis revealed that HCN4p-EGFP trans-gene was stably integrated into the chromosome of mouse AB1 ES cells. RT-PCR and immunostaining results showed similar expression of the specific cardiac pacemaker markers of the HCN4p-EGFP ES cells and its parental AB1 ES cell lines. Although HCN4p-EGFP trans-gene may have slight effect on the general mesodermal differentiation, it had no effect on the pluripotency of ES cells, on the transcription of cardiac specific factors and cardiac contractile proteins, and on the capability of ES cells to differentiate into pacemaker cells. Electrophysiological study indicated that HCN4p-GFP-positive cells revealed the spontaneous action potential, which was slowed by the treatment with 2 mM Cs(+), and expressed the hyperpolarization-activeted cation current I(f) encoded by HCN4 gene. By the approach of using stable transfectant of HCN4p-EGFP gene, the identification, isolation, and characterization of ES cell-derived pacemaking cells could be carried out.

EXPERIMENTAL STUDY ON DIFFERENTIATION OF BONE MARROW STROMA CELLS TO CARDIOMYOCYTES‐LIKE

Objective To investigate the ultrastructure and cell factor changes of BONE MARROW STROMA CELLS(BMSCs) after induction and differentiation into cardiomyocytes‐like, in order to provide theory foundation for the therapy of dilated cardiomyopathy(DCM) with BMSCs transplantation.Method BMSCs were isolated and proliferated in vitro, after induction and differentiation by 5‐azacytidine(5‐aza), they were observed by electromicroscopy to see the ultrastructure changes; RT‐PCR were also used to check cardiac‐special factors including ANP, BNP, α‐MHC, β‐MHC, comparing with the cardiomyocytes in primary culture in vitro.Result BMSCs were verified by immunohistochemistry that they differentiated into cardiomyocytes‐like; under electromicroscopy, glycogensome and myofibril can be seen in cell plasm, which was similar to cardiomyocyte in primary culture. RT‐PCR showed that BMSCs expressed cardiac‐specific factors, including ANP, BNP, α‐MHC, β‐MHC after induction and differentiation.Conclusion After induction by 5‐aza, BMSCs were similar to cardiomyocytes in primary culture in ultrastructure and cardiac‐specific factors expression, which suggested that they can be used for the therapy of DCM with BMSCs transplantation.

Lrrc10 is required for early heart development and function in zebrafish

Leucine-rich Repeat Containing protein 10 (LRRC10) has recently been identified as a cardiac-specific factor in mice. However, the function of this factor remains to be elucidated. In this study, we investigated the developmental roles of Lrrc10 using zebrafish as an animal model. Knockdown of Lrrc10 in zebrafish embryos (morphants) using morpholinos caused severe cardiac morphogenic defects including a cardiac looping failure accompanied by a large pericardial edema, and embryonic lethality between day 6 and 7 post fertilization. The Lrrc10 morphants exhibited cardiac functional defects as evidenced by a decrease in ejection fraction and cardiac output. Further investigations into the underlying mechanisms of the cardiac defects revealed that the number of cardiomyocyte was reduced in the morphants. Expression of two cardiac genes was deregulated in the morphants including an increase in atrial natriuretic factor, a hallmark for cardiac hypertrophy and failure, and a decrease in cardiac myosin light chain 2, an essential protein for cardiac contractility in zebrafish. Moreover, a reduced fluorescence intensity from NADH in the morphant heart was observed in live zebrafish embryos as compared to control. Taken together, the present study demonstrates that Lrrc10 is necessary for normal cardiac development and cardiac function in zebrafish embryos, which will enhance our understanding of congenital heart defects and heart disease.

Structure, expression, and functional characterization of the mouse CLP-1 gene

Mouse CLP-1, a potential cardiac transcriptional regulatory factor, is encoded by a single copy gene lacking introns that is expressed into two mRNAs via alternative polyadenylation. Both mRNAs encode the same 41 kDa protein, a novel protein that is 85.3% homologous with a human homologue called HIS1. Mouse CLP-1 is widely expressed in a number of tissues as well as in early development and is localized to the nucleus. The CLP-1 gene promoter is active in different cell types and sequence analysis shows a number of potential binding sites for cardiogenic transcription factors such as Nkx2.5 and GATA-4, indicating a potential role in development. CLP-1 appears to ‘squelch’ the cardiac MLC-2v promoter in a concentration-dependent manner in cardiac but not other cell types, suggesting that CLP-1 may be interacting with a cardiac-specific factor to regulate cardiac MLC-2v expression. The overall expression pattern of CLP-1 is similar to that of LCR-F1 and Oct-1, two widely expressed transcription factors that also play specific roles in the transcription of cell-specific genes. CLP-1 may be a transcriptional mediator capable of interacting with and potentiating cell-specific transcription factors.

Structural Organization and Transcription Regulation of Nuclear Genes Encoding the Mammalian Cytochrome c Oxidase Complex

Cytochrome c Oxidase (COX) is the terminal component of the bacterial as well as the mitochondrial respiratory chain complex that catalyzes the conversion of redox energy to ATP. In eukaryotes, the oligomeric enzyme is bound to mitochondrial innermembrane with subunits ranging from 7 to 13. Thus, its biosynthesis involves a coordinate interplay between nuclear and mitochondrial genomes. The largest subunits, I, II, and III, which represent the catalytic core of the enzyme, are encoded by the mitochondrial DNA and are synthesized within the mitochondria. The rest of the smaller subunits implicated in the regulatory function are encoded on the nuclear DNA and imported into mitochondria following their synthesis in the cytosol. Some of the nuclear coded subunits are expressed in tissue and developmental specific isologs. The ubiquitous subunits IV, Va, Vb, VIb, VIc, VIIb, VIIc, and VIII (L) are detected in all the tissues, although the mRNA levels for the individual subunits vary in different tissues. The tissue specific isologs VIa (H), VIIa (H), and VIII (H) are exclusive to heart and skeletal muscle. cDNA sequence analysis of nuclear coded subunits reveals 60 to 90% conservation among species both at the amino acid and nucleotide level, with the exception of subunit VIII, which exhibits 40 to 80% interspecies homology. Functional genes for COX subunits IV, Vb, VIa 'L' & 'H', VIIa 'L' & 'H', VIIc and VIII (H) from different mammalian species and their 5' flanking putative promoter regions have been sequenced and extensively characterized. The size of the genes range from 2 to 10 kb in length. Although the number of introns and exons are identical between different species for a given gene, the size varies across the species. A majority of COX genes investigated, with the exception of muscle-specific COXVIII(H) gene, lack the canonical 'TATAA' sequence and contain GC-rich sequences at the immediate upstream region of transcription start site(s). In this respect, the promoter structure of COX genes resemble those of many house-keeping genes. The ubiquitous COX genes show extensive 5' heterogeneity with multiple transcription initiation sites that bind to both general as well as specialized transcription factors such as YY1 and GABP (NRF2/ets). The transcription activity of the promoter in most of the ubiquitous genes is regulated by factors binding to the 5' upstream Sp1, NRF1, GABP (NRF2), and YY1 sites. Additionally, the murine COXVb promoter contains a negative regulatory region that encompasses the binding motifs with partial or full consensus to YY1, GTG, CArG, and ets. Interestingly, the muscle-specific COX genes contain a number of striated muscle-specific regulatory motifs such as E box, CArG, and MEF2 at the proximal promoter regions. While the regulation of COXVIa (H) gene involves factors binding to both MEF2 and E box in a skeletal muscle-specific fashion, the COXVIII (H) gene is regulated by factors binding to two tandomly duplicated E boxes in both skeletal and cardiac myocytes. The cardiac-specific factor has been suggested to be a novel bHLH protein. Mammalian COX genes provide a valuable system to study mechanisms of coordinated regulation of nuclear and mitochondrial genes. The presence of conserved sequence motifs common to several of the nuclear genes, which encode mitochondrial proteins, suggest a possible regulatory function by common physiological factors like heme/O2/carbon source. Thus, a well-orchestrated regulatory control and cross talks between the nuclear and mitochondrial genomes in response to changes in the mitochondrial metabolic conditions are key factors in the overall regulation of mitochondrial biogenesis.