Cardiac Hegemony of Senescence. ACTA ACUST UNITED AC. 2013;2. [PMID: 24349878 DOI: 10.1007/s13670-013-0064-3]

Overexpression of GREM1 Improves the Survival Capacity of Aged Cardiac Mesenchymal Progenitor Cells via Upregulation of the ERK/NRF2-Associated Antioxidant Signal Pathway

Ischemic heart disease is the leading cause of mortality in the United States. Progenitor cell therapy can restore myocardial structure and function. However, its efficacy is severely limited by cell aging and senescence. Gremlin-1 (GREM1), a member of the bone morphogenetic protein antagonist family, has been implicated in cell proliferation and survival. However, GREM1's role in cell aging and senescence has never been investigated in human cardiac mesenchymal progenitor cells (hMPCs). Therefore, this study assessed the hypothesis that overexpression of GREM1 rejuvenates the cardiac regenerative potential of aging hMPCs to a youthful stage and therefore allows better capacity for myocardial repair. We recently reported that a subpopulation of hMPCs with low mitochondrial membrane potential can be sorted from right atrial appendage-derived cells in patients with cardiomyopathy and exhibit cardiac reparative capacity in a mouse model of myocardial infarction. In this study, lentiviral particles were used to overexpress GREM1 in these hMPCs. Protein and mRNA expression were assessed through Western blot and RT-qPCR. FACS analysis for Annexin V/PI staining and lactate dehydrogenase assay were used to assess cell survival. It was observed that cell aging and cell senescence led to a decrease in GREM1 expression. In addition, overexpression of GREM1 led to a decrease in expression of senescence genes. Overexpression of GREM1 led to no significant change in cell proliferation. However, GREM1 appeared to have an anti-apoptotic effect, with an increase in survival and decrease in cytotoxicity evident in GREM1-overexpressing hMPCs. Overexpressing GREM1 also induced cytoprotective properties by decreasing reactive oxidative species and mitochondrial membrane potential. This result was associated with increased expression of antioxidant proteins, such as SOD1 and catalase, and activation of the ERK/NRF2 survival signal pathway. Inhibition of ERK led to a decrease in GREM1-mediated rejuvenation in terms of cell survival, which suggests that an ERK-dependent pathway may be involved. Taken altogether, these results indicate that overexpression of GREM1 can allow aging hMPCs to adopt a more robust phenotype with improved survival capacity, which is associated with an activated ERK/NRF2 antioxidant signal pathway.

Chronic low-grade inflammation in heart failure with preserved ejection fraction

Heart failure (HF) with preserved ejection fraction (HFpEF) is currently the predominant form of HF with a dramatic increase in risk with age. Low-grade inflammation, as occurs with aging (termed "inflammaging"), is a common feature of HFpEF pathology. Suppression of proinflammatory pathways has been associated with attenuated HFpEF disease severity and better outcomes. From this perspective, inflammasome signaling plays a central role in mediating chronic inflammation and cardiovascular disease progression. However, the causal link between the inflammasome-immune signaling axis on the age-dependent progression of HFpEF remains conjectural. In this review, we summarize the current understanding of the role of inflammatory pathways in age-dependent cardiac function decline. We will also evaluate recent advances and evidence regarding the inflammatory pathway in the pathophysiology of HFpEF, with special attention to inflammasome signaling.

AICAR and nicotinamide treatment synergistically augment the proliferation and attenuate senescence-associated changes in mesenchymal stromal cells

Background

Mesenchymal stromal cell (MSC) stemness capacity diminishes over prolonged in vitro culture, which negatively affects their application in regenerative medicine. To slow down the senescence of MSCs, here, we have evaluated the in vitro effects of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, and nicotinamide (NAM), an activator of sirtuin1 (SIRT1).

Methods

Human adipose-derived MSCs were cultured to passage (P) 5. Subsequently, the cells were grown in either normal medium alone (control group), the medium supplemented with AICAR (1 mM) and NAM (5 mM), or in the presence of both for 5 weeks to P10. Cell proliferation, differentiation capacity, level of apoptosis and autophagy, morphological changes, total cellular reactive oxygen species (ROS), and activity of mTORC1 and AMPK were compared among different treatment groups.

Results

MSCs treated with AICAR, NAM, or both displayed an increase in proliferation and osteogenic differentiation, which was augmented in the group receiving both. Treatment with AICAR or NAM led to decreased expression of β-galactosidase, reduced accumulation of dysfunctional lysosomes, and characteristic morphologic features of young MSCs. Furthermore, while NAM administration could significantly reduce the total cellular ROS in aged MSCs, AICAR treatment did not. Moreover, AICAR-treated cells possess a high proliferation capacity; however, they also show the highest level of cellular apoptosis. The observed effects of AICAR and NAM were in light of the attenuated mTORC1 activity and increased AMPK activity and autophagy.

Conclusions

Selective inhibition of mTORC1 by AICAR and NAM boosts autophagy, retains MSCs’ self-renewal and multi-lineage differentiation capacity, and postpones senescence-associated changes after prolonged in vitro culture. Additionally, co-administration of AICAR and NAM shows an additive or probably a synergistic effect on cellular senescence.

Aging: A cell source limiting factor in tissue engineering

Tissue engineering has yet to reach its ideal goal, i.e. creating profitable off-the-shelf tissues and organs, designing scaffolds and three-dimensional tissue architectures that can maintain the blood supply, proper biomaterial selection, and identifying the most efficient cell source for use in cell therapy and tissue engineering. These are still the major challenges in this field. Regarding the identification of the most appropriate cell source, aging as a factor that affects both somatic and stem cells and limits their function and applications is a preventable and, at least to some extents, a reversible phenomenon. Here, we reviewed different stem cell types, namely embryonic stem cells, adult stem cells, induced pluripotent stem cells, and genetically modified stem cells, as well as their sources, i.e. autologous, allogeneic, and xenogeneic sources. Afterward, we approached aging by discussing the functional decline of aged stem cells and different intrinsic and extrinsic factors that are involved in stem cell aging including replicative senescence and Hayflick limit, autophagy, epigenetic changes, miRNAs, mTOR and AMPK pathways, and the role of mitochondria in stem cell senescence. Finally, various interventions for rejuvenation and geroprotection of stem cells are discussed. These interventions can be applied in cell therapy and tissue engineering methods to conquer aging as a limiting factor, both in original cell source and in the in vitro proliferated cells.

Cardiac ageing: extrinsic and intrinsic factors in cellular renewal and senescence

Cardiac ageing manifests as a decline in function leading to heart failure. At the cellular level, ageing entails decreased replicative capacity and dysregulation of cellular processes in myocardial and nonmyocyte cells. Various extrinsic parameters, such as lifestyle and environment, integrate important signalling pathways, such as those involving inflammation and oxidative stress, with intrinsic molecular mechanisms underlying resistance versus progression to cellular senescence. Mitigation of cardiac functional decline in an ageing organism requires the activation of enhanced maintenance and reparative capacity, thereby overcoming inherent endogenous limitations to retaining a youthful phenotype. Deciphering the molecular mechanisms underlying dysregulation of cellular function and renewal reveals potential interventional targets to attenuate degenerative processes at the cellular and systemic levels to improve quality of life for our ageing population. In this Review, we discuss the roles of extrinsic and intrinsic factors in cardiac ageing. Animal models of cardiac ageing are summarized, followed by an overview of the current and possible future treatments to mitigate the deleterious effects of cardiac ageing.

Adult Cardiomyocyte Cell Cycle Detour: Off-ramp to Quiescent Destinations

Ability to promote completion of mitotic cycling of adult mammalian cardiomyocytes remains an intractable and vexing challenge, despite being one of the most sought after 'holy grails' of cardiovascular research. While some of the struggle is attributable to adult cardiomyocytes themselves that are notoriously post-mitotic, another contributory factor rests with difficulty in definitive tracking of adult cardiomyocyte cell cycle and lack of rigorous measures to track proliferation in situ. This review summarizes past, present, and future directions to promote adult mammalian cardiomyocyte cell cycle progression, proliferation, and renewal. Establishing relationship(s) between cardiomyocyte cell cycle progression and cellular biological properties is sorely needed to understand the mechanistic basis for cardiomyocyte cell cycle withdrawal to enhance cardiomyocyte cell cycle progression and mitosis.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

Single-Cell Transcriptomics of Human Mesenchymal Stem Cells Reveal Age-Related Cellular Subpopulation Depletion and Impaired Regenerative Function

Although bone marrow-derived mesenchymal stem cells (BM-MSCs) are widely recognized as promising therapeutic agents, the age-related impacts on cellular function remain largely uncharacterized. In this study, we found that BM-MSCs from young donors healed wounds in a xenograft model faster compared with their aged counterparts (p < .001). Given this significant healing advantage, we then used single-cell transcriptomic analysis to provide potential molecular insights into these observations. We found that the young cells contained a higher proportion of cells characterized by a higher expression of genes involved in tissue regeneration. In addition, we identified a unique, quiescent subpopulation that was exclusively present in young donor cells. Together, these findings may explain a novel mechanism for the enhanced healing capacity of young stem cells and may have implications for autologous cell therapy in the extremes of age. Stem Cells 2019;37:240-246.

Long non-coding RNAs in the failing heart and vasculature

Following completion of the human genome, it became evident that the majority of our DNA is transcribed into non-coding RNAs (ncRNAs) instead of protein-coding messenger RNA. Deciphering the function of these ncRNAs, including both small- and long ncRNAs (lncRNAs), is an emerging field of research. LncRNAs have been associated with many disorders and a number have been identified as key regulators in the development and progression of disease, including cardiovascular disease (CVD). CVD causes millions of deaths worldwide, annually. Risk factors include coronary artery disease, high blood pressure and ageing. In this review, we will focus on the roles of lncRNAs in the cellular and molecular processes that underlie the development of CVD: cardiomyocyte hypertrophy, fibrosis, inflammation, vascular disease and ageing. Finally, we discuss the biomarker and therapeutic potential of lncRNAs.

Current Progress in the Rejuvenation of Aging Stem/Progenitor Cells for Improving the Therapeutic Effectiveness of Myocardial Repair

Ischemic heart disease affects a majority of people, especially elderly patients. Recent studies have utilized autologous adult stem/progenitor cells as a treatment option to heal cardiac tissue after myocardial infarction. However, donor cells from aging patients are more likely to be in a senescent stage. Rejuvenation is required to reverse the damage levied by aging and promote a youthful phenotype. This review aims to discuss current strategies that are effective in rejuvenating aging cardiac stem cells and represent novel therapeutic methods to treat the aging heart. Recent literature mainly focuses on three approaches that aim to reverse cardiac aging: genetic modification, pharmaceutical administration, and optimization of extracellular factors. In vitro genetic modification can be used to overexpress or knock down certain genes and allow for reversal of the aging phenotype. Pharmaceutical administration is another approach that allows for manipulation of signaling pathways related to cell proliferation and cell senescence. Since the stem cell niche can contribute to the age-related decline in stem cell function, rejuvenation strategies also include optimization of extracellular factors. Overall, improving the intrinsic properties of aging stem cells as well as the surrounding environment allows these cells to adopt a phenotype similar to their younger counterparts.

Beyond cardiomyocyte loss: Role of Notch in cardiac aging

The knowledge of the cellular events occurring in the aging heart has dramatically expanded in the last decade and is expected to further grow in years to come. It is now clear that impaired function and loss of cardiomyocytes are major features of cardiac aging, but other events are likewise important. In particular, accumulating experimental evidence highlights the importance of fibroblast and cardiac progenitor cell (CPC) dysfunction. The Notch pathway regulates cardiomyocyte, fibroblast, and CPC activity and, thus, may be critically involved in heart disease associated with advanced age, especially heart failure. In a translational perspective, thorough investigation of the Notch system in the aging myocardium may lead to the identification of molecular targets for novel therapies for age-related cardiac disease.

Resveratrol Ameliorates Mitochondrial Elongation via Drp1/Parkin/PINK1 Signaling in Senescent-Like Cardiomyocytes

Resveratrol is widely known for its antiaging properties and exerts cardiovascular protective effects in different experimental models. The role of resveratrol in regulating mitochondrial functions and dynamics during the cardiac aging process remains poorly understood. In this study, the effects of resveratrol on mitochondrial morphology and mitochondrial depolarization and on expressions of Drp1, parkin, PINK1, and LC3 were investigated in H9c2 cells after D-galactose treatment that induced senescent-like cardiomyocytes. The results show that downregulation of Drp1 markedly increased mitochondrial elongation. Senescent-like cardiomyocytes were more resistant to CCCP-induced mitochondrial depolarization, which was accompanied by suppressed expression of parkin, PINK1, and LC3-II. Resveratrol treatment significantly increased Drp1 expression, ameliorated mitochondrial elongation, and increased the mitochondrial translocations of parkin and PINK1. In addition, resveratrol significantly enhanced LC3-II expression and decreased TOM20-labeled mitochondrial content. Resveratrol also suppressed the phosphorylation of parkin and PINK1, which may relate to its abilities to degrade the impaired mitochondria in senescent-like cardiomyocytes. These findings show that suppressing mitochondrial elongation in a Drp1-dependent manner is involved in the effect of resveratrol on attenuating the development of aging cardiomyocytes. Activation of parkin and PINK1 may be a potential mechanism of resveratrol for treating cardiovascular complications related to aging.

Rejuvenating the senescent heart

PURPOSE OF REVIEW

The purpose of this review is to provide an update on the cardiac stem cell field with an emphasis on aging and to suggest some relevant strategies directed toward rejuvenation of the senescent heart.

RECENT FINDINGS

Stem cells were long considered as a fountain of youth and were assumed to be equipped against any form of aging effect. However, it is now clear that stem cells suffer the consequences of aging as well. With the discovery that cardiac stem cells reside in the heart comes the question whether these cells are also impaired upon aging. As cardiac stem cell properties are also altered with age, autologous stem cell-based therapy to treat heart failure will benefit from new improved strategies.

SUMMARY

With the goal to improve stem cell properties that are impaired upon aging, some strategies are highlighted. Genetic modification of adult human cardiac progenitor cells prior to autologous stem cell-based therapy, delivery of the next generation of stem cells such as CardioChimeras and CardioClusters, and improvement of the myocardial environment with rejuvenating factors constitute some of the possibilities and are discussed in more detail in this review.

Aging disrupts cell subpopulation dynamics and diminishes the function of mesenchymal stem cells

Advanced age is associated with an increased risk of vascular morbidity, attributable in part to impairments in new blood vessel formation. Mesenchymal stem cells (MSCs) have previously been shown to play an important role in neovascularization and deficiencies in these cells have been described in aged patients. Here we utilize single cell transcriptional analysis to determine the effect of aging on MSC population dynamics. We identify an age-related depletion of a subpopulation of MSCs characterized by a pro-vascular transcriptional profile. Supporting this finding, we demonstrate that aged MSCs are also significantly compromised in their ability to support vascular network formation in vitro and in vivo. Finally, aged MSCs are unable to rescue age-associated impairments in cutaneous wound healing. Taken together, these data suggest that age-related changes in MSC population dynamics result in impaired therapeutic potential of aged progenitor cells. These findings have critical implications for therapeutic cell source decisions (autologous versus allogeneic) and indicate the necessity of strategies to improve functionality of aged MSCs.

A comprehensive study of myocardial redox homeostasis in naturally and mimetically aged rats

Age-related myocardial dysfunction has important implications with impaired redox homeostasis. Current study focused on investigation of redox homeostasis and histopathological changes in the myocardium of mimetically (MA), naturally aged (NA), and young control (YC) rats. Chronic D-galactose administration to young male Wistar rats (5 months old) was used to set up experimental aging models. We investigated 16 different oxidative damage biomarkers which have evaluated redox homeostasis of cellular macromolecules such as protein, lipid, and DNA. As a protein oxidation biomarker, advanced oxidation end products, protein carbonyl groups, protein-bound advanced glycation end products, dityrosine, kynurenine, and N-formylkynurenine concentrations in MA and NA rats were found to be significantly higher compared to those in YC rats. On the other hand, the levels of protein thiol groups were not significantly different between groups, whereas lipid peroxidation biomarkers such as conjugated diens, lipid hydroperoxides, and malondialdehyde in MA and NA rats were found to be significantly higher in comparison to those in YCs. For the assessment of oxidative DNA damage, we analyzed eight hydroxy-5'-deoxyguanosine concentrations of MA and NA groups which were higher than YCs. As an antioxidant status in the MA and NA groups, Cu-Zn superoxide dismutase, ferric reducing antioxidant power, and total thiol levels were lower than those in the YCs. Only nonprotein thiol levels were not significantly different. We also observed similar histopathological changes in MA and NA rats. We concluded that the mimetic aging model could be considered as a reliable experimental model for myocardial senescence.