Collagen chain mRNAs in isolated heart cells from young and adult rats

Primary cardiac fibroblast cell culture: methodological considerations for physiologically relevant conditions

Primary cardiac fibroblast (CF) tissue culture is a necessary tool for interrogating specific signaling mechanisms that dictate the phenotypic heterogeneity observed in vivo in different disease states. Traditional approaches that use tissue culture plastic and nutrient-rich medium have been shown to induce CF activation and, therefore, alter CF subpopulation composition. This shift away from in vivo phenotypes complicate the interpretation of results through the lens of the animal model. As the field works to identify CF diversity, these methodological flaws have begun to be addressed and more studies are focused on the dynamic interaction of CFs with their environment. This review focuses on the aspects of tissue culture that impact CF activation and, therefore, require consideration when designing in vitro experiments. The complexity of CF biology overlaid onto diverse model systems highlight the need for study-specific optimization and validation.

Epigenetic Regulation of Fibroblasts and Crosstalk between Cardiomyocytes and Non-Myocyte Cells in Cardiac Fibrosis

Epigenetic mechanisms and cell crosstalk have been shown to play important roles in the initiation and progression of cardiac fibrosis. This review article aims to provide a thorough overview of the epigenetic mechanisms involved in fibroblast regulation. During fibrosis, fibroblast epigenetic regulation encompasses a multitude of mechanisms, including DNA methylation, histone acetylation and methylation, and chromatin remodeling. These mechanisms regulate the phenotype of fibroblasts and the extracellular matrix composition by modulating gene expression, thereby orchestrating the progression of cardiac fibrosis. Moreover, cardiac fibrosis disrupts normal cardiac function by imposing myocardial mechanical stress and compromising cardiac electrical conduction. This review article also delves into the intricate crosstalk between cardiomyocytes and non-cardiomyocytes in the heart. A comprehensive understanding of the mechanisms governing epigenetic regulation and cell crosstalk in cardiac fibrosis is critical for the development of effective therapeutic strategies. Further research is warranted to unravel the precise molecular mechanisms underpinning these processes and to identify potential therapeutic targets.

Elucidating the role of circNFIB in myocardial fibrosis alleviation by endogenous sulfur dioxide

BACKGROUND

To investigate the role of circNFIB in the alleviation of myocardial fibrosis by endogenous sulfur dioxide (SO₂).

METHODS

We stimulated cultured neonatal rat cardiac fibroblasts with transforming growth factor-β1 (TGF-β1) and developed an in vitro myocardial fibrosis model. Lentivirus vectors containing aspartate aminotransferase 1 (AAT1) cDNA were used to overexpress AAT1, and siRNA was used to silence circNFIB. The SO₂, collagen, circNFIB, Wnt/β-catenin, and p38 MAPK pathways were examined in each group.

RESULTS

In the in vitro TGF-β1-induced myocardial fibrosis model, endogenous SO₂/AAT1 expression was significantly decreased, and collagen levels in the cell supernatant and type I and III collagen expression, as well as α-SMA expression, were all significantly increased. TGF-β1 also significantly reduced circNFIB expression. AAT1 overexpression significantly reduced myocardial fibrosis while significantly increasing circNFIB expression. Endogenous SO₂ alleviated myocardial fibrosis after circNFIB expression was blocked. We discovered that circNFIB plays an important role in the alleviation of myocardial fibrosis by endogenous SO₂ by inhibiting the Wnt/β-catenin and p38 MAPK pathways.

CONCLUSION

Endogenous SO₂ promotes circNFIB expression, which inhibits the Wnt/β-catenin and p38 MAPK signaling pathways, consequently alleviating myocardial fibrosis.

Transcriptome and morphological analysis on the heart in gestational protein-restricted aging male rat offspring

Background: Adverse factors that influence embryo/fetal development are correlated with increased risk of cardiovascular disease (CVD), type-2 diabetes, arterial hypertension, obesity, insulin resistance, impaired kidney development, psychiatric disorders, and enhanced susceptibility to oxidative stress and inflammatory processes in adulthood. Human and experimental studies have demonstrated a reciprocal relationship between birthweight and cardiovascular diseases, implying intrauterine adverse events in the onset of these abnormalities. In this way, it is plausible that confirmed functional and morphological heart changes caused by gestational protein restriction could be related to epigenetic effects anticipating cardiovascular disorders and reducing the survival time of these animals. Methods: Wistar rats were divided into two groups according to the protein diet content offered during the pregnancy: a normal protein diet (NP, 17%) or a Low-protein diet (LP, 6%). The arterial pressure was measured, and the cardiac mass, cardiomyocytes area, gene expression, collagen content, and immunostaining of proteins were performed in the cardiac tissue of male 62-weeks old NP compared to LP offspring. Results: In the current study, we showed a low birthweight followed by catch-up growth phenomena associated with high blood pressure development, increased heart collagen content, and cardiomyocyte area in 62-week-old LP offspring. mRNA sequencing analysis identified changes in the expression level of 137 genes, considering genes with a p-value < 0.05. No gene was. Significantly changed according to the adj-p-value. After gene-to-gene biological evaluation and relevance, the study demonstrated significant differences in genes linked to inflammatory activity, oxidative stress, apoptosis process, autophagy, hypertrophy, and fibrosis pathways resulting in heart function disorders. Conclusion: The present study suggests that gestational protein restriction leads to early cardiac diseases in the LP progeny. It is hypothesized that heart dysfunction is associated with fibrosis, myocyte hypertrophy, and multiple abnormal gene expression. Considering the above findings, it may suppose a close link between maternal protein restriction, specific gene expression, and progressive heart failure.

Chimeric galectin-3 and collagens: Biomarkers and potential therapeutic targets in fibroproliferative diseases

Fibrosis, stiffening and scarring of an organ/tissue due to genetic abnormalities, environmental factors, infection, and/or injury, is responsible for > 40% of all deaths in the industrialized world, and to date, there is no cure for it despite extensive research and numerous clinical trials. Several biomarkers have been identified, but no effective therapeutic targets are available. Human galectin-3 is a chimeric gene product formed by the fusion of the internal domain of the collagen alpha gene [N-terminal domain (ND)] at the 5'-end of galectin-1 [C-terminal domain (CRD)] that appeared during evolution together with vertebrates. Due to the overlapping structural similarities between collagen and galectin-3 and their shared susceptibility to cleavage by matrix metalloproteases to generate circulating collagen-like peptides, this review will discuss present knowledge on the role of collagen and galectin-3 as biomarkers of fibrosis. We will also highlight the need for transformative approaches targeting both the ND and CRD domains of galectin-3, since glycoconjugate binding by the CRD is triggered by ND-mediated oligomerization and the therapies targeted only at the CRD have so far achieved limited success.

Consequences of PDGFRα+ fibroblast reduction in adult murine hearts

Fibroblasts produce the majority of collagen in the heart and are thought to regulate extracellular matrix (ECM) turnover. Although fibrosis accompanies many cardiac pathologies and is generally deleterious, the role of fibroblasts in maintaining the basal ECM network and in fibrosis in vivo is poorly understood. We genetically ablated fibroblasts in mice to evaluate the impact on homeostasis of adult ECM and cardiac function after injury. Fibroblast-ablated mice demonstrated a substantive reduction in cardiac fibroblasts, but fibrillar collagen and the ECM proteome were not overtly altered when evaluated by quantitative mass spectrometry and N-terminomics. However, the distribution and quantity of collagen VI, microfibrillar collagen that forms an open network with the basement membrane, was reduced. In fibroblast-ablated mice, cardiac function was better preserved following angiotensin II/phenylephrine (AngII/PE)-induced fibrosis and myocardial infarction (MI). Analysis of cardiomyocyte function demonstrated altered sarcomere shortening and slowed calcium decline in both uninjured and AngII/PE-infused fibroblast-ablated mice. After MI, the residual resident fibroblasts responded to injury, albeit with reduced proliferation and numbers immediately after injury. These results indicate that the adult mouse heart tolerates a significant degree of fibroblast loss with a potentially beneficial impact on cardiac function after injury. The cardioprotective effect of controlled fibroblast reduction may have therapeutic value in heart disease.

Regulation of extracellular matrix composition by fibroblasts during perinatal cardiac maturation

BACKGROUND

Cardiac fibroblasts are the main non-myocyte population responsible for extracellular matrix (ECM) production. During perinatal development, fibroblast expansion coincides with the transition from hyperplastic to hypertrophic myocardial growth. Therefore, we investigated the consequences of fibroblast loss at the time of cardiomyocyte maturation by depleting fibroblasts in the perinatal mouse.

METHODS AND RESULTS

We evaluated the microenvironment of the perinatal heart in the absence of fibroblasts and the potential functional impact of fibroblast loss in regulation of cardiomyocyte cell cycle arrest and binucleation. Cre-mediated expression of diphtheria toxin A in PDGFRα expressing cells immediately after birth eliminated 70-80% of the cardiac fibroblasts. At postnatal day 5, hearts lacking fibroblasts appeared similar to controls with normal morphology and comparable numbers of endothelial and smooth muscle cells, despite a pronounced reduction in fibrillar collagen. Immunoblotting and proteomic analysis of control and fibroblast-deficient hearts identified differential abundance of several ECM proteins. In addition, fibroblast loss decreased tissue stiffness and resulted in increased cardiomyocyte mitotic index, DNA synthesis, and cytokinesis. Moreover, decellularized matrix from fibroblast-deficient hearts promoted cardiomyocyte DNA replication. While cardiac architecture was not overtly affected by fibroblast reduction, few pups survived past postnatal day 11, suggesting an overall requirement for PDGFRα expressing fibroblasts.

CONCLUSIONS

These studies demonstrate the key role of fibroblasts in matrix production and cardiomyocyte cross-talk during mouse perinatal heart maturation and revealed that fibroblast-derived ECM may modulate cardiomyocyte maturation in vivo. Neonatal depletion of fibroblasts demonstrated that although hearts can tolerate reduced ECM composition, fibroblast loss eventually leads to perinatal death as the approach simultaneously reduced fibroblast populations in other organs.

Cardiac Fibrosis in the Pressure Overloaded Left and Right Ventricle as a Therapeutic Target

Myocardial fibrosis is a remodeling process of the extracellular matrix (ECM) following cardiac stress. "Replacement fibrosis" is a term used to describe wound healing in the acute phase of an injury, such as myocardial infarction. In striking contrast, ECM remodeling following chronic pressure overload insidiously develops over time as "reactive fibrosis" leading to diffuse interstitial and perivascular collagen deposition that continuously perturbs the function of the left (L) or the right ventricle (RV). Examples for pressure-overload conditions resulting in reactive fibrosis in the LV are systemic hypertension or aortic stenosis, whereas pulmonary arterial hypertension (PAH) or congenital heart disease with right sided obstructive lesions such as pulmonary stenosis result in RV reactive fibrosis. In-depth phenotyping of cardiac fibrosis has made it increasingly clear that both forms, replacement and reactive fibrosis co-exist in various etiologies of heart failure. While the role of fibrosis in the pathogenesis of RV heart failure needs further assessment, reactive fibrosis in the LV is a pathological hallmark of adverse cardiac remodeling that is correlated with or potentially might even drive both development and progression of heart failure (HF). Further, LV reactive fibrosis predicts adverse outcome in various myocardial diseases and contributes to arrhythmias. The ability to effectively block pathological ECM remodeling of the LV is therefore an important medical need. At a cellular level, the cardiac fibroblast takes center stage in reactive fibrotic remodeling of the heart. Activation and proliferation of endogenous fibroblast populations are the major source of synthesis, secretion, and deposition of collagens in response to a variety of stimuli. Enzymes residing in the ECM are responsible for collagen maturation and cross-linking. Highly cross-linked type I collagen stiffens the ventricles and predominates over more elastic type III collagen in pressure-overloaded conditions. Research has attempted to identify pro-fibrotic drivers causing fibrotic remodeling. Single key factors such as Transforming Growth Factor β (TGFβ) have been described and subsequently targeted to test their usefulness in inhibiting fibrosis in cultured fibroblasts of the ventricles, and in animal models of cardiac fibrosis. More recently, modulation of phenotypic behaviors like inhibition of proliferating fibroblasts has emerged as a strategy to reduce pathogenic cardiac fibroblast numbers in the heart. Some studies targeting LV reactive fibrosis as outlined above have successfully led to improvements of cardiac structure and function in relevant animal models. For the RV, fibrosis research is needed to better understand the evolution and roles of fibrosis in RV failure. RV fibrosis is seen as an integral part of RV remodeling and presents at varying degrees in patients with PAH and animal models replicating the disease of RV afterload. The extent to which ECM remodeling impacts RV function and thus patient survival is less clear. In this review, we describe differences as well as common characteristics and key players in ECM remodeling of the LV vs. the RV in response to pressure overload. We review pre-clinical studies assessing the effect of anti-fibrotic drug candidates on LV and RV function and their premise for clinical testing. Finally, we discuss the mode of action, safety and efficacy of anti-fibrotic drugs currently tested for the treatment of left HF in clinical trials, which might guide development of new approaches to target right heart failure. We touch upon important considerations and knowledge gaps to be addressed for future clinical testing of anti-fibrotic cardiac therapies.

Regulation of Cardiac Fibroblast GLS1 Expression by Scleraxis

Fibrosis is an energy-intensive process requiring the activation of fibroblasts to myofibroblasts, resulting in the increased synthesis of extracellular matrix proteins. Little is known about the transcriptional control of energy metabolism in cardiac fibroblast activation, but glutaminolysis has been implicated in liver and lung fibrosis. Here we explored how pro-fibrotic TGFβ and its effector scleraxis, which drive cardiac fibroblast activation, regulate genes involved in glutaminolysis, particularly the rate-limiting enzyme glutaminase (GLS1). The GLS1 inhibitor CB-839 attenuated TGFβ-induced fibroblast activation. Cardiac fibroblast activation to myofibroblasts by scleraxis overexpression increased glutaminolysis gene expression, including GLS1, while cardiac fibroblasts from scleraxis-null mice showed reduced expression. TGFβ induced GLS1 expression and increased intracellular glutamine and glutamate levels, indicative of increased glutaminolysis, but in scleraxis knockout cells, these measures were attenuated, and the response to TGFβ was lost. The knockdown of scleraxis in activated cardiac fibroblasts reduced GLS1 expression by 75%. Scleraxis transactivated the human GLS1 promoter in luciferase reporter assays, and this effect was dependent on a key scleraxis-binding E-box motif. These results implicate scleraxis-mediated GLS1 expression as a key regulator of glutaminolysis in cardiac fibroblast activation, and blocking scleraxis in this process may provide a means of starving fibroblasts of the energy required for fibrosis.

Corneal fibroblast collagen type IV negative feedback modulation of TGF beta: A fibrosis modulating system likely active in other organs

Collagen type IV (COL IV) is a major component of basement membranes (BM) in all organs. It serves functions related to BM organization and modulates the passage of growth factors from one tissue compartment to another. COL IV binds transforming growth factor (TGF) beta-1 and TGF beta-2 and, therefore, is a major modulator of TGF beta pro-fibrotic functions. After fibrotic corneal injury, TGF beta enters into the stroma from the tears, epithelium, endothelium and/or aqueous humor and markedly upregulates COL IV production in corneal fibroblasts in the adjacent stroma far removed from BMs. It is hypothesized this non-BM stromal COL IV binds TGF beta-1 (and likely TGF beta-2) in competition with the binding of the growth factors to TGF beta cognate receptors and serves as a negative feedback regulatory pathway to mitigate the effects of TGF beta on stromal cells, including reducing the developmental transition of corneal fibroblasts and fibrocytes into myofibroblasts. Losartan, a known TGF beta signaling inhibitor, when applied topically to the cornea after fibrotic injury, alters this COL IV-TGF beta pathway by down-regulating COL IV production by corneal fibroblasts. Non-BM COL IV produced in response to injuries in other organs, including the lung, skin, liver, kidney, and gut, may participate in similar COL IV-TGF beta pathways and have an important role in controlling TGF beta pro-fibrotic effects in these organs.

Extracellular Matrix in Heart Disease: Focus on Circulating Collagen Type I and III Derived Peptides as Biomarkers of Myocardial Fibrosis and Their Potential in the Prognosis of Heart Failure: A Concise Review

Accumulating evidence indicates that two major proteins are responsible for the structural coherence of bounding cardiomyocytes. These biomolecules are known as myocardial fibrillar collagen type I (COL1) and type III (COL3). In addition, fibronectin, laminin, fibrillin, elastin, glycoproteins, and proteoglycans take part in the formation of cardiac extracellular matrix (ECM). In physiological conditions, collagen synthesis and degradation in human cardiac ECM are well-regulated processes, but they can be impaired in certain cardiovascular diseases, such as heart failure (HF). Myocardial remodeling is part of the central mechanism of HF and involves cardiomyocyte injury and cardiac fibrosis due to increased fibrillar collagen accumulation. COL1 and COL3 are predominantly involved in this process. Specific products identified as collagen-derived peptides are released in the circulation as a result of abnormal COL1 and COL3 turnover and myocardial remodeling in HF and can be detected in patients' sera. The role of these products in the pathogenesis of cardiac fibrosis and the possible clinical implications are the focus of numerous investigations. This paper reviews recent studies on COL1- and COL3-derived peptides in patients with HF. Their potential application as indicators of myocardial fibrosis and prognostic markers of HF is also highlighted.

Novel factors that activate and deactivate cardiac fibroblasts: A new perspective for treatment of cardiac fibrosis

Heart disease with attendant cardiac fibrosis kills more patients in developed countries than any other disease, including cancer. We highlight the recent literature on factors that activate and also deactivate cardiac fibroblasts. Activation of cardiac fibroblasts results in myofibroblasts phenotype which incorporates aSMA to stress fibres, express ED-A fibronectin, elevated PDGFRα and are hypersecretory ECM components. These cells facilitate both acute wound healing (infarct site) and chronic cardiac fibrosis. Quiescent fibroblasts are associated with normal myocardial tissue and provide relatively slow turnover of the ECM. Deactivation of activated myofibroblasts is a much less studied phenomenon. In this context, SKI is a known negative regulator of TGFb₁ /Smad signalling, and thus may share functional similarity to PPARγ activation. The discovery of SKI's potent anti-fibrotic role, and its ability to deactivate and/or myofibroblasts is featured and contrasted with PPARγ. While myofibroblasts are typically recruited from pools of potential precursor cells in a variety of organs, the importance of activation of resident cardiac fibroblasts has been recently emphasised. Myofibroblasts deposit ECM components at an elevated rate and contribute to both systolic and diastolic dysfunction with attendant cardiac fibrosis. A major knowledge gap exists as to specific proteins that may signal for fibroblast deactivation. As SKI may be a functionally pluripotent protein, we suggest that it serves as a scaffold to proteins other than R-Smads and associated Smad signal proteins, and thus its anti-fibrotic effects may extend beyond binding R-Smads. While cardiac fibrosis is causal to heart failure, the treatment of cardiac fibrosis is hampered by the lack of availability of effective pharmacological anti-fibrotic agents. The current review will provide an overview of work highlighting novel factors which cause fibroblast activation and deactivation to underscore putative therapeutic avenues for improving disease outcomes in cardiac patients with fibrosed hearts.

Yes-Associated Protein (Yap) Is Up-Regulated in Heart Failure and Promotes Cardiac Fibroblast Proliferation

Left ventricular (LV) heart failure (HF) is a significant and increasing cause of death worldwide. HF is characterized by myocardial remodeling and excessive fibrosis. Transcriptional co-activator Yes-associated protein (Yap), the downstream effector of HIPPO signaling pathway, is an essential factor in cardiomyocyte survival; however, its status in human LV HF is not entirely elucidated. Here, we report that Yap is elevated in LV tissue of patients with HF, and is associated with down-regulation of its upstream inhibitor HIPPO component large tumor suppressor 1 (LATS1) activation as well as upregulation of the fibrosis marker connective tissue growth factor (CTGF). Applying the established profibrotic combined stress of TGFβ and hypoxia to human ventricular cardiac fibroblasts in vitro increased Yap protein levels, down-regulated LATS1 activation, increased cell proliferation and collagen I production, and decreased ribosomal protein S6 and S6 kinase phosphorylation, a hallmark of mTOR activation, without any significant effect on mTOR and raptor protein expression or phosphorylation of mTOR or 4E-binding protein 1 (4EBP1), a downstream effector of mTOR pathway. As previously reported in various cell types, TGFβ/hypoxia also enhanced cardiac fibroblast Akt and ERK1/2 phosphorylation, which was similar to our observation in LV tissues from HF patients. Further, depletion of Yap reduced TGFβ/hypoxia-induced cardiac fibroblast proliferation and Akt phosphorylation at Ser 473 and Thr308, without any significant effect on TGFβ/hypoxia-induced ERK1/2 activation or reduction in S6 and S6 kinase activities. Taken together, these data demonstrate that Yap is a mediator that promotes human cardiac fibroblast proliferation and suggest its possible contribution to remodeling of the LV, opening the door to further studies to decipher the cell-specific roles of Yap signaling in human HF.

Complex Relationship Between Cardiac Fibroblasts and Cardiomyocytes in Health and Disease

Cardiac fibroblasts are the primary cell type responsible for deposition of extracellular matrix in the heart, providing support to the contracting myocardium and contributing to a myriad of physiological signaling processes. Despite the importance of fibrosis in processes of wound healing, excessive fibroblast proliferation and activation can lead to pathological remodeling, driving heart failure and the onset of arrhythmias. Our understanding of the mechanisms driving the cardiac fibroblast activation and proliferation is expanding, and evidence for their direct and indirect effects on cardiac myocyte function is accumulating. In this review, we focus on the importance of the fibroblast-to-myofibroblast transition and the cross talk of cardiac fibroblasts with cardiac myocytes. We also consider the current use of models used to explore these questions.

Exposure to Δ9-tetrahydrocannabinol during rat pregnancy leads to impaired cardiac dysfunction in postnatal life

BACKGROUND

Cannabis use in pregnancy leads to fetal growth restriction (FGR), but the long-term effects on cardiac function in the offspring are unknown, despite the fact that fetal growth deficits are associated with an increased risk of developing postnatal cardiovascular disease. We hypothesize that maternal exposure to Δ9-tetrahydrocannabinol (Δ9-THC) during pregnancy will impair fetal development, leading to cardiac dysfunction in the offspring.

METHODS

Pregnant Wistar rats were randomly selected and administered 3 mg/kg of Δ9-THC or saline as a vehicle daily via intraperitoneal injection from gestational days 6 to 22, followed by echocardiogram analysis of cardiac function on offspring at postnatal days 1 and 21. Heart tissue was harvested from the offspring at 3 weeks for molecular analysis of cardiac remodelling.

RESULTS

Exposure to Δ9-THC during pregnancy led to FGR with a significant decrease in heart-to-body weight ratios at birth. By 3 weeks, pups exhibited catch-up growth associated with significantly greater left ventricle anterior wall thickness with a decrease in cardiac output. Moreover, these Δ9-THC-exposed offsprings exhibited increased expression of collagen I and III, decreased matrix metallopeptidase-2 expression, and increased inactivation of glycogen synthase kinase-3β, all associated with cardiac remodelling.

CONCLUSIONS

Collectively, these data suggest that Δ9-THC-exposed FGR offspring undergo postnatal catch-up growth concomitant with cardiac remodelling and impaired cardiac function early in life.

IMPACT

To date, the long-term effects of perinatal Δ9-THC (the main psychoactive component) exposure on the cardiac function in the offspring remain unknown. We demonstrated, for the first time, that exposure to Δ9-THC alone during rat pregnancy results in significantly smaller hearts relative to body weight. These Δ9-THC-exposed offsprings exhibited postnatal catch-up growth concomitant with cardiac remodelling and impaired cardiac function. Given the increased popularity of cannabis use in pregnancy along with rising Δ9-THC concentrations, this study, for the first time, identifies the risk of perinatal Δ9-THC exposure on early postnatal cardiovascular health.

Roles of Biomarkers in Myocardial Fibrosis

Myocardial fibrosis is observed in various cardiovascular diseases and plays a key role in the impairment of cardiac function. Endomyocardial biopsy, as the gold standard for the diagnosis of myocardial fibrosis, has limitations in terms of clinical application. Therefore, biomarkers have been recommended for noninvasive assessment of myocardial fibrosis. This review discusses the role of biomarkers in myocardial fibrosis from the perspective of collagen.

Cells, Materials, and Fabrication Processes for Cardiac Tissue Engineering

Cardiovascular disease is the number one killer worldwide, with myocardial infarction (MI) responsible for approximately 1 in 6 deaths. The lack of endogenous regenerative capacity, added to the deleterious remodelling programme set into motion by myocardial necrosis, turns MI into a progressively debilitating disease, which current pharmacological therapy cannot halt. The advent of Regenerative Therapies over 2 decades ago kick-started a whole new scientific field whose aim was to prevent or even reverse the pathological processes of MI. As a highly dynamic organ, the heart displays a tight association between 3D structure and function, with the non-cellular components, mainly the cardiac extracellular matrix (ECM), playing both fundamental active and passive roles. Tissue engineering aims to reproduce this tissue architecture and function in order to fabricate replicas able to mimic or even substitute damaged organs. Recent advances in cell reprogramming and refinement of methods for additive manufacturing have played a critical role in the development of clinically relevant engineered cardiovascular tissues. This review focuses on the generation of human cardiac tissues for therapy, paying special attention to human pluripotent stem cells and their derivatives. We provide a perspective on progress in regenerative medicine from the early stages of cell therapy to the present day, as well as an overview of cellular processes, materials and fabrication strategies currently under investigation. Finally, we summarise current clinical applications and reflect on the most urgent needs and gaps to be filled for efficient translation to the clinical arena.

Proteome analysis of secretions from human monocyte-derived macrophages post-exposure to biomaterials and the effect of secretions on cardiac fibroblast fibrotic character

The use of exogenous biomolecules (BM) for the purpose of repairing and regenerating damaged cardiac tissue can yield serious side effects if used for prolonged periods. As well, such strategies can be cost prohibitive depending on the regiment and period of time applied. Alternatively, autologous monocytes/monocyte-derived macrophages (MDM) can provide a viable path towards generating an endogenous source of stimulatory BM. Biomaterials are often considered as delivery vehicles to generate unique profiles of such BM in tissues or to deliver autologous cells, that can influence the nature of BM produced by the cells. MDM cultured on a degradable polar hydrophobic ionic (D-PHI) polyurethane has previously demonstrated a propensity to increase select anti-inflammatory cytokines, and therefore there is good rationale to further investigate a broader spectrum of the cells' BM in order to provide a more complete proteomic analysis of human MDM secretions induced by D-PHI. Further, it is of interest to assess the potential of such BM to influence cells involved in the reparative state of vital tissues such as those that affect cardiac cell function. Hence, this current study examines the proteomic profile of MDM secretions using mass spectrometry for the first time, along with ELISA, following their culture on D-PHI, and compares them to two important reference materials, poly(lactic-co-glycolic acid) (PLGA) and tissue culture polystyrene (TCPS). Secretions collected from D-PHI cultured MDM led to higher levels of regenerative BM, AGRN, TGFBI and ANXA5, but lower levels of pro-fibrotic BM, MMP7, IL-1β, IL-6 and TNFα,  when compared to MDM secretions collected from PLGA and TCPS. In the application to cardiac cell function, the secretion collected from D-PHI cultured MDM led to more human cardiac fibroblast (HCFs) migration. A lower collagen gel contraction induced by MDM secretions collected from D-PHI was supported by gene array analysis for human fibrosis-related genes. The implication of these findings is that more tailored biomaterials such as D-PHI, may lead to a lower pro-inflammatory phenotype of macrophages when used in cardiac tissue constructs, thereby enabling the development of vehicles for the delivery of interventional therapies, or be applied as coatings for sensor implants in cardiac tissue that minimize fibrosis. The general approach of using synthetic biomaterials in order to induce MDM secretions in a manner that will guide favorable regeneration will be critical in making the choice of biomaterials for tissue regeneration work in the future. STATEMENT OF SIGNIFICANCE: Immune modulation strategies currently applied in cardiac tissue repair are mainly based on the delivery of defined exogenous biomolecules. However, the use of such biomolecules may pose wide ranging systemic effects, thereby rendering them clinically less practical. The chemistry of biomaterials (used as a potential targeted delivery modality to circumvent the broad systemic effects of biomolecules) can not only affect acute and chronic toxicity but also alters the timeframe of the wound healing cascade. In this context, monocytes/monocyte-derive macrophages (MDM) can be harnessed as an immune modulating strategy to promote wound healing by an appropriate choice of the biomaterial. However, there are limited reports on the complete proteome analysis of MDM and their reaction of biomaterial related interventions on cardiac tissues and cells. No studies to date have demonstrated the complete proteome of MDM secretions when these cells were cultured on a non-traditional immune modulatory ionomeric polyurethane D-PHI film. This study demonstrated that MDM cultured on D-PHI expressed significantly higher levels of AGRN, TGFBI and ANXA5 but lower levels of MMP7, IL-1β, IL-6 and TNFα when compared to MDM cultured on a well-established degradable biomaterials in the medical field, e.g. PLGA and TCPS, which are often used as the relative standards for cell culture work in the biomaterials field. The implications of these findings have relevance to the repair of cardiac tissues. In another aspect of the work, human cardiac fibroblasts showed significantly lower contractility (low collagen gel contraction and low levels of ACTA2) when cultured in the presence of MDM secretions collected after culturing them on D-PHI compared to PLGA and TCPS. The findings place emphasis on the importance of making the choice of biomaterials for tissue engineering and regenerative medicine applied to their use in cardiac tissue repair.

Matrix metalloproteinases regulate ECM accumulation but not larval heart growth in Drosophila melanogaster

The Drosophila heart provides a simple model to examine the remodelling of muscle insertions with growth, extracellular matrix (ECM) turnover, and fibrosis. Between hatching and pupation, the Drosophila heart increases in length five-fold. If major cardiac ECM components are secreted remotely, how is ECM "self assembly" regulated? We explored whether ECM proteases were required to maintain the morphology of a growing heart while the cardiac ECM expanded. An increase in expression of Drosophila's single tissue inhibitor of metalloproteinase (TIMP), or reduced function of metalloproteinase MMP2, resulted in fibrosis and ectopic deposition of two ECM Collagens; type-IV and fibrillar Pericardin. Significant accumulations of Collagen-IV (Viking) developed on the pericardium and in the lumen of the heart. Congenital defects in Pericardin deposition misdirected further assembly in the larva. Reduced metalloproteinase activity during growth also increased Pericardin fibre accumulation in ECM suspending the heart. Although MMP2 expression was required to remodel and position cardiomyocyte cell junctions, reduced MMP function did not impair expansion of the heart. A previous study revealed that MMP2 negatively regulates the size of the luminal cell surface in the embryonic heart. Cardiomyocytes align at the midline, but do not adhere to enclose a heart lumen in MMP2 mutant embryos. Nevertheless, these embryos hatch and produce viable larvae with bifurcated hearts, indicating a secondary pathway to lumen formation between ipsilateral cardiomyocytes. MMP-mediated remodelling of the ECM is required for organogenesis, and to prevent assembly of excess or ectopic ECM protein during growth. MMPs are not essential for normal growth of the Drosophila heart.

Elevated dual specificity protein phosphatase 4 in cardiomyopathy caused by lamin A/C gene mutation is primarily ERK1/2-dependent and its depletion improves cardiac function and survival

Mutations in the lamin A/C gene (LMNA) encoding the nuclear intermediate filament proteins lamins A and C cause a group of tissue-selective diseases, the most common of which is dilated cardiomyopathy (herein referred to as LMNA cardiomyopathy) with variable skeletal muscle involvement. We previously showed that cardiomyocyte-specific overexpression of dual specificity protein phosphatase 4 (DUSP4) is involved in the pathogenesis of LMNA cardiomyopathy. However, how mutations in LMNA activate Dusp4 expression and whether it is necessary for the development of LMNA cardiomyopathy are currently unknown. We now show that female LmnaH222P/H222P mice, a model for LMNA cardiomyopathy, have increased Dusp4 expression and hyperactivation of extracellular signal-regulated kinase (ERK) 1/2 with delayed kinetics relative to male mice, consistent with the sex-dependent delay in the onset and progression of disease. Mechanistically, we show that the H222P amino acid substitution in lamin A enhances its binding to ERK1/2 and increases sequestration at the nuclear envelope. Finally, we show that genetic deletion of Dusp4 has beneficial effects on heart function and prolongs survival in LmnaH222P/H222P mice. These results further establish Dusp4 as a key contributor to the pathogenesis of LMNA cardiomyopathy and a potential target for drug therapy.

Phosphodiesterase expression in the normal and failing heart

The number of patients with heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF) is increasing, and for HFpEF, no therapies have clinical benefit. It has been hypothesized that PKG attenuates pathological remodelling, and increasing cGMP would be beneficial for patients with HF. However, neither the RELAX nor NEAT-HFpEF trial showed benefit. But there is still enthusiasm for increasing cGMP in patients with HF, which highlight the need to determine the expression of PDEs in cardiac muscle. This study used immunoblotting to examine the expression of the PDEs that have been suggested to be targets for therapy of HF in both canines (normal and HFpEF) and humans (normal and HFrEF). Our results demonstrate PDE1C and PDE3A are expressed in cardiac muscle, but we could not detect the expression of PDE2A, PDE5A, PDE7A and PDE9A in cardiac tissue lysates from either normal or failing hearts. Thus, one should not expect a clinical benefit for a therapy targeting these PDEs in heart failure, which highlights the importance of rigorous demonstration of the target of therapy prior to undertaking a clinical trial.

Dissecting the Role of the Extracellular Matrix in Heart Disease: Lessons from the Drosophila Genetic Model

The extracellular matrix (ECM) is a dynamic scaffold within organs and tissues that enables cell morphogenesis and provides structural support. Changes in the composition and organisation of the cardiac ECM are required for normal development. Congenital and age-related cardiac diseases can arise from mis-regulation of structural ECM proteins (Collagen, Laminin) or their receptors (Integrin). Key regulators of ECM turnover include matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of matrix metalloproteinases (TIMPs). MMP expression is increased in mice, pigs, and dogs with cardiomyopathy. The complexity and longevity of vertebrate animals makes a short-lived, genetically tractable model organism, such as Drosophila melanogaster, an attractive candidate for study. We survey ECM macromolecules and their role in heart development and growth, which are conserved between Drosophila and vertebrates, with focus upon the consequences of altered expression or distribution. The Drosophila heart resembles that of vertebrates during early development, and is amenable to in vivo analysis. Experimental manipulation of gene function in a tissue- or temporally-regulated manner can reveal the function of adhesion or ECM genes in the heart. Perturbation of the function of ECM proteins, or of the MMPs that facilitate ECM remodelling, induces cardiomyopathies in Drosophila, including cardiodilation, arrhythmia, and cardia bifida, that provide mechanistic insight into cardiac disease in mammals.

Differential ERK1/2 Signaling and Hypertrophic Response to Endothelin-1 in Cardiomyocytes from SHR and Wistar-Kyoto Rats: A Potential Target for Combination Therapy of Hypertension

Extracellular signal regulated kinase½ (ERK1/2) signaling is critical to endothelin-1 (ET-1)-induced cardiomyocyte hypertrophy. This study was to investigate ERK1/2 signaling and hypertrophic response to ET-1 stimulation in cardiomyocytes (CMs) from spontaneous hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Primary neonatal SHR and WKY CMs were exposed to ET-1 for up to 24 hrs. Minimal basal ERK1/2 phosphorylation was present in WKY CMs, while a significant baseline ERK1/2 phosphorylation was observed in SHR CMs. ET-1 induced a time- and dose-dependent increase in ERK1/2 phosphorylation in both SHR and WKY CMs. However, ET-1-induced ERK1/2 activation occurred much earlier with significantly higher peak phosphorylation level, and stayed elevated for longer duration in SHR CMs than that in WKY CMs. ET-1-induced hypertrophic response was more prominent in SHR CMs than that in WKY CMs as reflected by increased cell surface area, intracellular actin density, and protein synthesis. Pre-treatment with ERK1/2 phosphorylation inhibitor PD98059 completely prevented ET-1-induced ERK1/2 phosphorylation and increases in cell surface area and protein synthesis in SHR and WKY CMs. The specific PI3 kinase inhibitor LY294002 blocked ET-1-induced Akt and ERK1/2 phosphorylation, and protein synthesis in CMs. These data indicated that ERK1/2 signaling was differentially enhanced in CMs, and was associated with increased cardiac hypertrophic response to ET-1 in SHR. ET-1-induced ERK1/2 activation and cardiac hypertrophy appeared to be mediated via PI3 kinase/Akt signaling in SHR and WKY. The differential ERK1/2 activation in SHR CMs by ET-1 might represent a potential target for combination therapy of hypertension.

Aging and the cardiac collagen matrix: Novel mediators of fibrotic remodelling

Cardiovascular disease is a leading cause of death worldwide and there is a pressing need for new therapeutic strategies to treat such conditions. The risk of developing cardiovascular disease increases dramatically with age, yet the majority of experimental research is executed using young animals. The cardiac extracellular matrix (ECM), consisting predominantly of fibrillar collagen, preserves myocardial integrity, provides a means of force transmission and supports myocyte geometry. Disruptions to the finely balanced control of collagen synthesis, post-synthetic deposition, post-translational modification and degradation may have detrimental effects on myocardial functionality. It is now well established that the aged heart is characterized by fibrotic remodelling, but the mechanisms responsible for this are incompletely understood. Furthermore, studies using aged animal models suggest that interstitial remodelling with disease may be age-dependent. Thus with the identification of new therapeutic strategies targeting fibrotic remodelling, it may be necessary to consider age-dependent mechanisms. In this review, we discuss remodelling of the cardiac collagen matrix as a function of age, whilst highlighting potential novel mediators of age-dependent fibrotic pathways.

Circulating NOS3 modulates left ventricular remodeling following reperfused myocardial infarction

Purpose

Nitric oxide (NO) is constitutively produced and released from the endothelium and several blood cell types by the isoform 3 of the NO synthase (NOS3). We have shown that NO protects against myocardial ischemia/reperfusion (I/R) injury and that depletion of circulating NOS3 increases within 24h of ischemia/reperfusion the size of myocardial infarction (MI) in chimeric mice devoid of circulating NOS3. In the current study we hypothesized that circulating NOS3 also affects remodeling of the left ventricle following reperfused MI.

Methods

To analyze the role of circulating NOS3 we transplanted bone marrow of NOS3^−/− and wild type (WT) mice into WT mice, producing chimerae expressing NOS3 only in vascular endothelium (BC−/EC+) or in both, blood cells and vascular endothelium (BC+/EC+). Both groups underwent 60 min of coronary occlusion in a closed-chest model of reperfused MI. During the 3 weeks post MI, structural and functional LV remodeling was serially assessed (24h, 4d, 1w, 2w and 3w) by echocardiography. At 72 hours post MI, gene expression of several extracellular matrix (ECM) modifying molecules was determined by quantitative RT-PCR analysis. At 3 weeks post MI, hemodynamics were obtained by pressure catheter, scar size and collagen content were quantified post mortem by Gomori’s One-step trichrome staining.

Results

Three weeks post MI, LV end-systolic (53.2±5.9μl;***p≤0.001;n = 5) and end-diastolic volumes (82.7±5.6μl;*p<0.05;n = 5) were significantly increased in BC−/EC+, along with decreased LV developed pressure (67.5±1.8mmHg;n = 18;***p≤0.001) and increased scar size/left ventricle (19.5±1.5%;n = 13;**p≤0.01) compared to BC+/EC+ (ESV:35.6±2.2μl; EDV:69.1±2.6μl n = 8; LVDP:83.2±3.2mmHg;n = 24;scar size/LV13.8±0.7%;n = 16). Myocardial scar of BC−/EC+ was characterized by increased total collagen content (20.2±0.8%;n = 13;***p≤0.001) compared to BC+/EC+ (15.9±0.5;n = 16), and increased collagen type I and III subtypes.

Conclusion

Circulating NOS3 ameliorates maladaptive left ventricular remodeling following reperfused myocardial infarction.

The emperor's new clothes: PDE5 and the heart

Phosphodiesterase-5 (PDE5) is highly expressed in the pulmonary vasculature, but its expression in the myocardium is controversial. Cyclic guanosine monophosphate (cGMP) activates protein kinase G (PKG), which has been hypothesized to blunt cardiac hypertrophy and negative remodeling in heart failure. Although PDE5 has been suggested to play a significant role in the breakdown of cGMP in cardiomyocytes and hence PKG regulation in the myocardium, the RELAX trial, which tested effect of PDE5 inhibition on exercise capacity in patients with heart failure with preserved ejection fraction (HFpEF) failed to show a beneficial effect. These results highlight the controversy regarding the role and expression of PDE5 in the healthy and failing heart. This study used one- and two-dimensional electrophoresis and Western blotting to examine PDE5 expression in mouse (before and after trans-aortic constriction), dog (control and HFpEF) as well as human (healthy and failing) heart. We were unable to detect PDE5 in any cardiac tissue lysate, whereas PDE5 was present in the murine and bovine lung samples used as positive controls. These results indicate that if PDE5 is expressed in cardiac tissue, it is present in very low quantities, as PDE5 was not detected in either humans or any model of heart failure examined. Therefore in cardiac muscle, it is unlikely that PDE5 is involved the regulation of cGMP-PKG signaling, and hence PDE5 does not represent a suitable drug target for the treatment of cardiac hypertrophy. These results highlight the importance of rigorous investigation prior to clinical trial design.

KLF15 is an essential negative regulatory factor for the cardiac remodeling response to pressure overload

OBJECTIVE

To investigate the mechanism of Krüppel-like factor 15 (KLF15) in cardiac remodeling and interstitial fibrosis.

METHODS

A rat model was established by in vivo aortic coarctation followed by a period of pressure unloading and used to measure heart function, myocardial pathological changes, and KLF15, transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), and myocardin-related transcription factor A (MRTF-A) expression levels. In addition, cardiac fibroblasts were cultured in vitro and treated with KLF15-shRNA or KLF15 recombinant adenovirus to establish a TGF-β-mediated cardiac fibroblast hypertrophy model and analyze cell morphology, collagen secretion, and changes in the expression levels of 4 cytokines.

RESULTS

In vivo pressure overload impaired cardiac function and resulted in myocardial hypertrophy and fibrosis. These changes were accompanied by the downregulation of KLF15 mRNA levels and increased expression of the other factors. The response to unloading was the opposite. In in vitro cell experiments, by specifically targeting the KLF15 gene, changes in the expression levels of the 4 cytokines and the amounts of collagen I and III were observed.

CONCLUSIONS

In myocardial remodeling processes induced by mechanical or metabolic factors, KLF15 regulates TGF-β, CTGF, and MRTF-A expression and can ameliorate or even reverse myocardial fibrosis and improve cardiac function.

Stress sensitivity and mechanotransduction during heart development

Early in embryogenesis, the heart begins its rhythmic contractions as a tube that helps perfuse the nascent vasculature, but the embryonic heart soon changes shape and mechanical properties, like many other developing organs. A key question in the field is whether stresses in development impact the underlying gene circuits and, if so, how? Here, we attempt to address this question as we review the mechanical maturation of heart - and, to a limited extent, lung and blood - with a focus on a few key abundant structural proteins whose expression dynamics have been suggested to be directly sensitive to mechanical stress. In heart maturation, proliferating fibroblasts deposit increasing amounts of collagenous matrix in parallel with cardiomyocytes expressing more sarcomeric proteins that increase the contractile stress and strength of the tissue, which in turn pumps more blood at higher stress throughout the developing vasculature. Feedback of beating cardiomyocytes on the expression of matrix by fibroblasts seems a reasonable model, with both synthesis and turnover of matrix and contractile elements achieving a suitable balance. Based on emerging evidence for coiled-coil biopolymers that are tension-stabilized against degradation, a minimal network model of a dynamic cell-matrix interaction is proposed. This same concept is extended to nuclear mechanics as regulated by stress on the nuclear structural proteins called lamins, which are examined in part because of the prominence of mutations in these coiled-coil proteins in diseases of the heart, amongst other organs/tissues. Variations in lamin levels during development and across adult tissues are to some extent known and appear to correlate with extracellular matrix mechanics, which we illustrate across heart, lung, and blood development. The formal perspective here on the mechanochemistry of tissue development and homeostasis could provide a useful framework for 'big data' quantitative biology, particularly of stress-sensitive differentiation, maturation, and disease processes.

Molecular remodeling of left and right ventricular myocardium in chronic anthracycline cardiotoxicity and post-treatment follow up

Chronic anthracycline cardiotoxicity is a serious clinical issue with well characterized functional and histopathological hallmarks. However, molecular determinants of the toxic damage and associated myocardial remodeling remain to be established. Furthermore, details on the different propensity of the left and right ventricle (LV and RV, respectively) to the cardiotoxicity development are unknown. Hence, the aim of the investigation was to study molecular changes associated with remodeling of the LV and RV in chronic anthracycline cardiotoxicity and post-treatment follow up. The cardiotoxicity was induced in rabbits with daunorubicin (3 mg/kg/week for 10 weeks) and animals were sacrificed either at the end of the treatment or after an additional 10 weeks. Daunorubicin induced severe and irreversible cardiotoxicity associated with LV dysfunction and typical morphological alterations, whereas the myocardium of the RV showed only mild changes. Both ventricles also showed different expression of ANP after daunorubicin treatment. Daunorubicin impaired the expression of several sarcomeric proteins in the LV, which was not the case of the RV. In particular, a significant drop was found in titin and thick filament proteins at both mRNA and protein level and this might be connected with persistent LV down-regulation of GATA-4. In addition, the LV was more affected by treatment-induced perturbations in calcium handling proteins. LV cardiomyocytes showed marked up-regulation of desmin after the treatment and vimentin was mainly induced in LV fibroblasts, whereas only weaker changes were observed in the RV. Remodeling of extracellular matrix was almost exclusively found in the LV with particular induction of collagen I and IV. Hence, the present study describes profound molecular remodeling of myocytes, non-myocyte cells and extracellular matrix in response to chronic anthracycline treatment with marked asymmetry between LV and RV.

TWEAK-Fn14 Cytokine-Receptor Axis: A New Player of Myocardial Remodeling and Cardiac Failure

Tumor necrosis factor (TNF) has been firmly established as a pathogenic factor in heart failure, a significant socio-economic burden. In this review, we will explore the role of other members of the TNF/TNF receptor superfamily (TNFSF/TNFRSF) in cardiovascular diseases (CVDs) focusing on TWEAK and its receptor Fn14, new players in myocardial remodeling and heart failure. The TWEAK/Fn14 pathway controls a variety of cellular activities such as proliferation, differentiation, and apoptosis and has diverse biological functions in pathological mechanisms like inflammation and fibrosis that are associated with CVDs. Furthermore, it has recently been shown that the TWEAK/Fn14 axis is a positive regulator of cardiac hypertrophy and that deletion of Fn14 receptor protects from right heart fibrosis and dysfunction. We discuss the potential use of the TWEAK/Fn14 axis as biomarker for CVDs as well as therapeutic target for future treatment of human heart failure based on supporting data from animal models and in vitro studies. Collectively, existing data strongly suggest the TWEAK/Fn14 axis as a potential new therapeutic target for achieving cardiac protection in patients with CVDs.

N-acetyl-Ser-Asp-Lys-Pro inhibits interleukin-1β-mediated matrix metalloproteinase activation in cardiac fibroblasts

Myocardial matrix turnover involves a dynamic balance between collagen synthesis and degradation, which is regulated by matrix metalloproteinases (MMPs). N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) is a small peptide that inhibits cardiac inflammation and fibrosis. However, its role in MMP regulation is not known. Thus, we hypothesized that Ac-SDKP promotes MMP activation in cardiac fibroblasts and decreases collagen deposition via this mechanism. To that end, we tested the effects of Ac-SDKP on interleukin-1β (IL-1β; 5 ng/ml)-stimulated adult rat cardiac fibroblasts. We measured total collagenase activity, MMP-2, MMP-9, and MMP-13 expressions, and activity along with their inhibitors, tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. In order to examine the effects of Ac-SDKP on the signaling pathway that controls MMP transcription, we also measured nuclear factor-κB (NFκB) and p42/44 mitogen-activated protein kinase (MAPK) activation. Ac-SDKP did not alter collagenase or gelatinase activity in cardiac fibroblasts under basal conditions, but blunted the IL-1β-induced increase in total collagenase activity. Similarly, Ac-SDKP normalized the IL-1β-mediated increase in MMP-2 and MMP-9 activities and MMP-13 expression. Inhibition of MMPs by Ac-SDKP was associated with increased TIMP-1 and TIMP-2 expressions. Collagen production was not affected by Ac-SDKP, IL-1β, or a combination of both agents. Ac-SDKP blocked IL-1β-induced p42/44 phosphorylation and NFκB activation in cardiac fibroblasts. We concluded that the Ac-SDKP-inhibited collagenase expression and activation was associated with increased expression of TIMP-1 and TIMP-2. These pharmacological effects of Ac-SDKP may be linked to the inhibition of MAPK and NFκB pathway.

Hyperoxia and transforming growth factor β1 signaling in the post-ischemic mouse heart

AIMS

Following ischemic injury, myocardial healing and remodeling occur with characteristic myofibroblast trans-differentiation and scar formation. The current study tests the hypothesis that hyperoxia and nitric oxide (NO) regulate TGF-β1 signaling in the post-ischemic myocardium.

MAIN METHODS

C57BL/6 wild-type (WT), endothelial and inducible nitric oxide synthase knockout (eNOS(-/-) and iNOS(-/-)) mice were subjected to 30-min left anterior descending coronary artery occlusion followed by reperfusion. Myocardial tissue oxygenation was monitored with electron paramagnetic resonance oximetry. Protein expressions of TGF-β1, receptor-activated small mothers against decapentaplegic homolog (Smad), p21 and α-smooth muscle actin (α-SMA) were measured with enzyme-linked immunosorbent assay (ELISA), Western immunoblotting, and immunohistochemical staining.

KEY FINDINGS

There was a hyperoxic state in the post-ischemic myocardial tissue. Protein expressions of total and active TGF-β1, p-Smad2/3 over t-Smad2/3 ratio, p21, and α-SMA were significantly increased in WT mice compared to Sham control. Knockout of eNOS or iNOS further increased protein expression of these signals. The expression of α-SMA was more abundant in the infarct of eNOS(-/-) and iNOS(-/-) mice than WT mice. A protein band indicating nitration of TGF-β type-II receptor (TGFβRII) was observed from WT heart. Carbogen (95% O2 plus 5% CO2) treatment increased the ratio of p-Smad2/t-Smad2, which was inhibited by 10006329 EUK (EUK134) and sodium nitroprusside (SNP). In conclusion, hyperoxia up-regulated and NO/ONOO(-) inhibited cardiac TGF-β1 signaling and myofibroblast trans-differentiation.

SIGNIFICANCE

These findings may provide new insights in myocardial infarct healing and repair.

Extracellular matrix of mechanically stretched cardiac fibroblasts improves viability and metabolic activity of ventricular cells

BACKGROUND

In heart, the extracellular matrix (ECM), produced by cardiac fibroblasts, is a potent regulator of heart's function and growth, and provides a supportive scaffold for heart cells in vitro and in vivo. Cardiac fibroblasts are subjected to mechanical loading all the time in vivo. Therefore, the influences of mechanical loading on formation and bioactivity of cardiac fibroblasts ECM should be investigated.

METHODS

Rat cardiac fibroblasts were cultured on silicone elastic membranes and stimulated with mechanical cyclic stretch. After removing the cells, the ECMs coated on the membranes were prepared, some ECMs were treated with heparinase II (GAG-lyase), then the collagen, glycosaminoglycan (GAG) and ECM proteins were assayed. Isolated neonatal rat ventricular cells were seeded on ECM-coated membranes, the viability and lactate dehydrogenase (LDH) activity of the cells after 1-7 days of culture was assayed. In addition, the ATPase activity and related protein level, glucose consumption ratio and lactic acid production ratio of the ventricular cells were analyzed by spectrophotometric methods and Western blot.

RESULTS

The cyclic stretch increased collagen and GAG levels of the ECMs, and elevated protein levels of collagen I and fibronectin. Compared with the ECMs produced by unstretched cardiac fibroblasts, the ECMs of mechanically stretched fibroblasts improved viability and LDH activity, elevated the Na⁺/K⁺-ATPase activity, sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) activity and SERCA 2a protein level, glucose consumption ratio and lactic acid production ratio of ventricular cells seeded on them. The treatment with heparinase II reduced GAG levels of these ECMs, and lowered these metabolism-related indices of ventricular cells cultured on the ECMs.

CONCLUSIONS

Mechanical stretch promotes ECM formation of cardiac fibroblasts in vitro, the ECM of mechanically stretched cardiac fibroblasts improves metabolic activity of ventricular cells cultured in vitro, and the GAG of the ECMs is involved in regulating metabolic activity of ventricular cells.

Cardiac myofibroblasts: cells out of balance. A new thematic series

We are pleased to introduce a new thematic series dealing with cardiac fibrosis and its association with cardiovascular diseases. A wide variety of cardiovascular diseases are associated with cardiac fibrosis, which is now widely recognized to be not a secondary, but rather a primary contributor to cardiac dysfunction. The purpose of the current series of papers and reviews is to provide the reader with an up-to-date synopsis of the very latest research results and hypotheses that impact on cardiac fibrosis and disease.

Relationship between depression anxiety stress scale (DASS) and urinary hydroxyproline and proline concentrations in hospital workers

OBJECTIVES

Although increased reactive oxygen species (ROS) is caused by stress accelerates collagen degradation, there was no data on the relationship between stress and urinary hydroxyproline (Hyp) and proline (Pro), a good marker of collagen degradation. The purpose of this study was to evaluate the relationship between depression, anxiety, and stress (DAS) and concentrations of urinary Hyp and Pro.

METHODS

97 hospital employees aged 20 to 58 were asked to fill out comprehensive self-administrated questionnaires containing information about their medical history, lifestyle, length of the work year, shift-work and DAS. depression anxiety stress scale (DASS) was applied to evaluate chronic mental disorders. Urine samples were analyzed using high performance liquid chromatography (HPLC) with double derivatization for the assay of hydroxyproline and proline.

RESULTS

The mean value of Hyp and Pro concentration in all subjects was 194.1 ± 113.4 μmol/g and 568.2 ± 310.7 μmol/g. DASS values and urinary Pro concentrations were differentiated by sex (female > male, p < 0.05) and type of job (nurse > others, p < 0.05). In the stepwise multiple linear regressions, urinary Hyp and Pro concentrations were influenced by stress (Adjusted r2 = 0.051) and anxiety and job (Adjusted r2 = 0.199), respectively.

CONCLUSIONS

We found that stress and anxiety were correlated with urinary Hyp and Pro concentrations. To identifying a definite correlation, further study in large populations will be needed.

Attenuation of ischemic myocardial injury and dysfunction by cardiac fibroblast-derived factor(s)

Fibroblasts, the majority of non-cardiomyocytes in the heart, are known to release several kinds of substances such as cytokines and hormones that affect cell and tissue functions. We hypothesized that undefined substance (s) derived from cardiac fibroblasts may have the potential to protect against ischemic myocardium. To assess our hypothesis, using rats, we investigated: (1) the effect of cardiac fibroblast-conditioned medium (CM) on the viability of hypoxic cardiomyocytes in vitro, (2) the effect of CM on left ventricular (LV) function in global ischemia-reperfusion in an ex vive model, (3) the mechanism underlying cardioprotection by CM. Seventy-two hours after starting a hypoxic culture, the viability of cardiomyocytes was higher (P < 0.05) in the CM treated group (41.4%) compared to the control (20.5%). In Langendorff's preparation, 30 min after ischemia-reperfusion, LV end-diastolic pressure was lower, and LV developed pressure and -LVdP/dt were higher (P < 0.01 or P < 0.05) in the CM group than in the control, although coronary flow did not differ between the two groups. Pretreatment with a protein kinase C inhibitor or a mitochondrial ATP-sensitive K+ channel blocker attenuated these changes of LV function in the CM group. Such cardioprotection was achieved by a fraction of the CM having a molecular weight (MW) > 50,000, but not by that of the CM with a lower MW. In addition, a specific antibody against hepatocyte growth factor (HGF, MW is 84,000) did not reduce the cardioprotection afforded by CM. There may be an unknown cardioprotective substance other than HGF in rats, which mimics ischemic preconditioning and has MW > 50,000.

Free heme is a danger signal inducing expression of proinflammatory proteins in cultured cells derived from normal rat hearts

Endogenous molecules from damaged tissue act as danger signals to trigger or amplify the immune/inflammatory response. In this study, we examined whether free heme induced pro-inflammatory proteins in cultured cells derived from normal hearts and investigated the cells targeted by heme, together with its mechanism of action in these cells. We cultured collagenase-isolated heart-derived cells from normal rats and examined whether free heme induced pro-inflammatory proteins, reactive oxygen species (ROS) production and NF-κB activation, by quantitative RT-PCR, ELISA and flow cytometry. Free heme increased mRNA of various pro-inflammatory proteins in cultured cardiac resident cells (CCRC) (at least 100-fold) and induced intracellular ROS formation. Approximately 85-90% of CCRC are fibroblast/smooth muscle cells and 10-15% are CD11bc-positive macrophages; therefore to examine individual target cells, macrophage-deleted (CD11bc-negative) CCRC, primary cultured cells (cardiac fibroblasts, arterial smooth muscle cells and cardiac microvascular endothelial cells) and macrophage cells lines (NR8383) were similarly treated. Free heme activated NF-κB and induced expression of some pro-inflammatory proteins, including IL-1 and TNF-α in NR8383. On the other hand, macrophage-deleted CCRC strongly increased expression of these proteins on treatment with IL-1 or TNF-α, but not free heme. Induction of expression of pro-inflammatory proteins by free heme was not inhibited by intracellular ROS reduction, but by protease and proteasome inhibitors capable of regulating NF-κB. These data suggest that free heme strongly induces various pro-inflammatory proteins in injured hearts through NF-κB activation in cardiac resident macrophages and through cross-talk between macrophages and fibroblast/smooth muscle cells mediated inter alia by IL-1, TNF-α.

Proinflammatory cytokines in heart failure: double-edged swords

Increased circulating and intracardiac levels of proinflammatory cytokines have been associated with chronic heart failure. Following an initial insult, the increased production of proinflammatory cytokines, including TNF-α, IL-6, IL-1, and IL-18, jeopardizes the surrounding tissue through propagation of the inflammatory response and direct effects on the cardiac myocyte structure and function. Cardiac myocyte hypertrophy, contractile dysfunction, cardiac myocyte apoptosis, and extracellular matrix remodeling contribute enormously to the development and progression of chronic heart failure. Despite the identification of efficacious pharmacological regimens and introduction of mechanical interventions, chronic heart failure remains among the leading causes of mortality worldwide. To introduce novel therapeutic strategies that modulate the inflammatory response in the context of the failing heart, it is of prime importance to determine the contributions of TNF-α, IL-6, IL-1, and IL-18 in mediating cardiac adaptive and maladaptive responses, as well as delineating their downstream intracellular signaling pathways and their potential therapeutic implications.

The impact of vascular endothelial growth factor and basic fibroblast growth factor on cardiac fibroblasts grown under altered gravity conditions

BACKGROUND

Myocardium is very sensitive to gravitational changes. During a spaceflight cardiovascular atrophy paired with rhythm problems and orthostatic intolerance can occur. The aim of this study was to investigate the impact of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) on cardiac fibroblasts (CF) grown under altered gravity conditions.

METHODS

We examined the influence of exposure to a Random Positioning Machine (RPM) on CF, derived from porcine hearts. We focused on growth, extracellular matrix protein (ECMP) synthesis and apoptosis.

RESULTS

When cultured on a RPM, CF began to form 3D spheroids within 24h, irrespective of growth factor treatment. Exposure to RPM induced an increased synthesis of ECMP and also resulted in elevated apoptosis in adherent CF as measured by terminal deoxynucleotidyl transferase-mediated dUTP digoxigenin nick end labeling (TUNEL) analysis, 4',6-diamidino-2-phenylindole (DAPI) staining, and caspase-3 detection. bFGF and VEGF significantly decreased the amount of ECMP (collagen type I, III, chondroitin sulfate) in 1g and RPM cultures, and also significantly reduced the amount of apoptotic CF as well as caspase-3.

CONCLUSIONS

Altered gravity conditions on a RPM induced 3D growth, elevated ECMP synthesis and apoptosis in cardiac fibroblasts. Growth factor treatment attenuated programmed cell death and ECMP secretion.

Cardiac fibroblast to myofibroblast differentiation in vivo and in vitro: expression of focal adhesion components in neonatal and adult rat ventricular myofibroblasts

In fibrosing hearts, myofibroblasts are associated with cardiac extracellular matrix remodeling. Expression of key genes in the transition of cardiac fibroblast to myofibroblast phenotype in post-myocardial infarction heart and in vitro has not been well addressed. Contractile, focal adhesion-associated, receptor proteins, fibroblast growth factor-2 (FGF-2) expression, and motility were compared to assess phenotype in adult and neonatal rat cardiac fibroblasts and myofibroblasts. Neonatal and adult fibroblasts undergo phenotypic transition to myofibroblastic cells, marked by increased alpha-smooth muscle actin (alphaSMA), smooth muscle myosin heavy chain (SMemb), extra domain-A (ED-A) fibronectin, paxillin, tensin, FGF-2, and TbetaRII receptor. Elevated ED-A fibronectin confirmed fibroblast to supermature myofibroblastic phenotype transition. Presence of myofibroblasts in vivo was noted in sections of healed infarct scar after myocardial infarction, and their expression is similar to that in culture. Thus, cultured neonatal and adult cardiac fibroblasts transition to myofibroblasts in vitro and share expression profiles of cardiac myofibroblasts in vivo. Reduced motility with in vitro passage reflects enhanced production of focal adhesions.

Single mechano-gated channels activated by mechanical deformation of acutely isolated cardiac fibroblasts from rats

AIM

Mechanosensitive conductances were reported in cardiac fibroblasts, but the properties of single channels mediating their mechanosensitivity remain uncharacterized. The aim of this work was to investigate single mechano-gated channels (MGCs) activated by mechanical deformations of cardiac fibroblasts.

METHODS

Currents through single MGCs and mechanosensitive whole-cell currents were recorded from isolated rat atrial fibroblasts using the cell-attached and whole-cell patch-clamp configurations respectively. Defined mechanical stress was applied via the patch pipette used for the whole-cell recordings.

RESULTS

Under resting conditions occasional short openings of two types of single MGCs with conductances of 43 and 87 pS were observed. Both types of channels displayed a linear current-voltage relationship with the reversal potential around 0 mV. Small (1 microm) mechanical deformations affected neither single nor whole-cell mechano-gated currents. Cell compressions (2, 3 and 4 microm) augmented the whole-cell currents and increased the frequency and duration of single channel openings. Cell stretches (2, 3 and 4 microm) inactivated the whole-cell currents and abolished the activity of single MGCs. Gd(3+) (8 microm) blocked the whole-cell currents within 5 min. No single channel activity was observed in the cell-attached mode when Gd(3+) was added to the intrapipette solution. Cytochalasin D and colchicine (100 microm each) completely blocked both the whole-cell and single channel currents.

CONCLUSIONS

These findings show that rat atrial fibroblasts express two types of MGCs whose activity is governed by cell deformation. We conclude that fibroblasts can sense the direction of applied stress and contribute to mechano-electrical coupling in the heart.

Intramyocardial fibroblast myocyte communication

Cardiac fibroblasts are emerging as key components of normal cardiac function, as well as the response to stressors and injury. These most numerous cells of the heart interact with myocytes via paracrine mechanisms, alterations in extracellular matrix homeostasis, and direct cell-cell interactions. It is possible that they are a contributor to the inability of adult myocytes to proliferate and may influence cardiac progenitor biology. Furthering our understanding of how cardiac fibroblasts and myocytes interact may provide an avenue to novel treatments for heart failure prevention. This review discusses the most recent concepts in cardiac fibroblast-myocyte communication and areas of potential future research.

Cardiac fibroblasts are essential for the adaptive response of the murine heart to pressure overload

Fibroblasts, which are the most numerous cell type in the heart, interact with cardiomyocytes in vitro and affect their function; however, they are considered to play a secondary role in cardiac hypertrophy and failure. Here we have shown that cardiac fibroblasts are essential for the protective and hypertrophic myocardial responses to pressure overload in vivo in mice. Haploinsufficiency of the transcription factor-encoding gene Krüppel-like factor 5 (Klf5) suppressed cardiac fibrosis and hypertrophy elicited by moderate-intensity pressure overload, whereas cardiomyocyte-specific Klf5 deletion did not alter the hypertrophic responses. By contrast, cardiac fibroblast-specific Klf5 deletion ameliorated cardiac hypertrophy and fibrosis, indicating that KLF5 in fibroblasts is important for the response to pressure overload and that cardiac fibroblasts are required for cardiomyocyte hypertrophy. High-intensity pressure overload caused severe heart failure and early death in mice with Klf5-null fibroblasts. KLF5 transactivated Igf1 in cardiac fibroblasts, and IGF-1 subsequently acted in a paracrine fashion to induce hypertrophic responses in cardiomyocytes. Igf1 induction was essential for cardioprotective responses, as administration of a peptide inhibitor of IGF-1 severely exacerbated heart failure induced by high-intensity pressure overload. Thus, cardiac fibroblasts play a pivotal role in the myocardial adaptive response to pressure overload, and this role is partly controlled by KLF5. Modulation of cardiac fibroblast function may provide a novel strategy for treating heart failure, with KLF5 serving as an attractive target.

Origin of cardiac fibroblasts and the role of periostin

Cardiac fibroblasts are the most populous nonmyocyte cell type within the mature heart and are required for extracellular matrix synthesis and deposition, generation of the cardiac skeleton, and to electrically insulate the atria from the ventricles. Significantly, cardiac fibroblasts have also been shown to play an important role in cardiomyocyte growth and expansion of the ventricular chambers during heart development. Although there are currently no cardiac fibroblast-restricted molecular markers, it is generally envisaged that the majority of the cardiac fibroblasts are derived from the proepicardium via epithelial-to-mesenchymal transformation. However, still relatively little is known about when and where the cardiac fibroblasts cells are generated, the lineage of each cell, and how cardiac fibroblasts move to reside in their final position throughout all four cardiac chambers. In this review, we summarize the present understanding regarding the function of Periostin, a useful marker of the noncardiomyocyte lineages, and its role during cardiac morphogenesis. Characterization of the cardiac fibroblast lineage and identification of the signals that maintain, expand and regulate their differentiation will be required to improve our understanding of cardiac function in both normal and pathophysiological states.

c-Ski, Smurf2, and Arkadia as regulators of TGF-β signaling: new targets for managing myofibroblast function and cardiac fibrosisThis article is one of a selection of papers published in a special issue celebrating the 125th anniversary of the Faculty of Medicine at the University of Manitoba

Recent studies demonstrate the critical role of the extracellular matrix in the organization of parenchymal cells in the heart. Thus, an understanding of the modes of regulation of matrix production by cardiac myofibroblasts is essential. Transforming growth factor β (TGF-β) signaling is transduced through the canonical Smad pathway, and the involvement of this pathway in matrix synthesis and other processes requires precise control. Inhibition of Smad signaling may be achieved at the receptor level through the targeting of the TGF-β type I receptors with an inhibitory Smad7 / Smurf2 complex, or at the transcriptional level through c-Ski / receptor-Smad / co-mediator Smad4 interactions. Conversely, Arkadia protein intensifies TGF-β-induced effects by marking c-Ski and inhibitory Smad7 for destruction. The study of these TGF-β mediators is essential for future treatment of fibrotic disease, and this review highlights recent relevant findings that may impact our understanding of cardiac fibrosis.

Transcriptional and posttranscriptional regulators of biglycan in cardiac fibroblasts

Biglycan, a small leucine-rich proteoglycan, is essential for scar formation and preservation of hemodynamic function after myocardial infarction, as shown in biglycan-knockout mice. Because of this important role in cardiac pathophysiology, we aimed to identify regulators of biglycan expression and posttranslational modifications in cardiac fibroblasts. Cardiac fibroblasts were isolated from neonatal Wistar-Kyoto rats and used in the first passage. Expression of biglycan was analyzed after metabolic labeling with [(35)S]-sulfate by SDS-polyacrylamide gel electrophoresis and molecular sieve chromatography; mRNA expression was examined by Northern analysis and real-time RT-PCR. Serum, thrombin, transforming growth factor beta1 (TGFbeta 1) and platelet-derived growth factor BB (PDGF-BB) strongly increased [(35)S]-labeled proteoglycan levels. Tumor necrosis factor alpha further increased the stimulatory effect of PDGF-BB. PDGF-BB increased glycosaminoglycan (GAG) chain length as shown by molecular sieve chromatography after beta-elimination to release GAG chains. Nitric oxide was the only negative regulator of biglycan as evidenced by marked downregulation in response to DETA-NO ((Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate), a long acting nitric oxide donor and SNAP (S-nitroso-N-acetyl-l,l-penicillamine), which completely inhibited PDGF-BB-induced secretion of total [(35)S]-labeled proteoglycans and biglycan mRNA expression. Of note, the molecular weight of biglycan GAG chains was even further increased by NO donors compared to control and PDGF-BB stimulation. The current results suggest that in cardiac fibroblasts, biglycan is induced by a variety of stimuli including serum, thrombin and growth factors such as PDGF-BB and TGFbeta1. This response is counteracted by NO and enhanced by TNFalpha. Interestingly, both up- and downregulation were associated with posttranslational increase of GAG chain length.