Telomerase expression in the mammalian heart

Cardiomyocyte Regeneration in the mdx Mouse Model of Nonischemic Cardiomyopathy

Endogenous regeneration has been demonstrated in the mammalian heart after ischemic injury. However, approximately one-third of cases of heart failure are secondary to nonischemic heart disease and cardiac regeneration in these cases remains relatively unexplored. We, therefore, aimed at quantifying the rate of new cardiomyocyte formation at different stages of nonischemic cardiomyopathy. Six-, 12-, 29-, and 44-week-old mdx mice received a 7 day pulse of BrdU. Quantification of isolated cardiomyocyte nuclei was undertaken using cytometric analysis to exclude nondiploid nuclei. Between 6–7 and 12–13 weeks, there was a statistically significant increase in the number of BrdU-labeled nuclei in the mdx hearts compared with wild-type controls. This difference was lost by the 29–30 week time point, and a significant decrease in cardiomyocyte generation was observed in both the control and mdx hearts by 44–45 weeks. Immunohistochemical analysis demonstrated BrdU-labeled nuclei exclusively in mononucleated cardiomyocytes. This study demonstrates cardiomyocyte regeneration in a nonischemic model of mammalian cardiomyopathy, controlling for changes in nuclear ploidy, which is lost with age, and confirms a decrease in baseline rates of cardiomyocyte regeneration with aging. While not attempting to address the cellular source of regeneration, it confirms the potential utility of innate regeneration as a therapeutic target.

Telomerase expression confers cardioprotection in the adult mouse heart after acute myocardial infarction

Coronary heart disease is one of the main causes of death in the developed world, and treatment success remains modest, with high mortality rates within 1 year after myocardial infarction (MI). Thus, new therapeutic targets and effective treatments are necessary. Short telomeres are risk factors for age-associated diseases, including heart disease. Here we address the potential of telomerase (Tert) activation in prevention of heart failure after MI in adult mice. We use adeno-associated viruses for cardiac-specific Tert expression. We find that upon MI, hearts expressing Tert show attenuated cardiac dilation, improved ventricular function and smaller infarct scars concomitant with increased mouse survival by 17% compared with controls. Furthermore, Tert treatment results in elongated telomeres, increased numbers of Ki67 and pH3-positive cardiomyocytes and a gene expression switch towards a regeneration signature of neonatal mice. Our work suggests telomerase activation could be a therapeutic strategy to prevent heart failure after MI.

The convergence of fracture repair and stem cells: interplay of genes, aging, environmental factors and disease

The complexity of fracture repair makes it an ideal process for studying the interplay between the molecular, cellular, tissue, and organ level events involved in tissue regeneration. Additionally, as fracture repair recapitulates many of the processes that occur during embryonic development, investigations of fracture repair provide insights regarding skeletal embryogenesis. Specifically, inflammation, signaling, gene expression, cellular proliferation and differentiation, osteogenesis, chondrogenesis, angiogenesis, and remodeling represent the complex array of interdependent biological events that occur during fracture repair. Here we review studies of bone regeneration in genetically modified mouse models, during aging, following environmental exposure, and in the setting of disease that provide insights regarding the role of multipotent cells and their regulation during fracture repair. Complementary animal models and ongoing scientific discoveries define an increasing number of molecular and cellular targets to reduce the morbidity and complications associated with fracture repair. Last, some new and exciting areas of stem cell research such as the contribution of mitochondria function, limb regeneration signaling, and microRNA (miRNA) posttranscriptional regulation are all likely to further contribute to our understanding of fracture repair as an active branch of regenerative medicine.

Concise review: heart regeneration and the role of cardiac stem cells

Acute myocardial infarction leads to irreversible loss of cardiac myocytes, thereby diminishing the pump function of the heart. As a result, the strenuous workload imposed on the remaining cardiac myocytes often gives rise to subsequent cell loss until the vicious circle ends in chronic heart failure (CHF). Thus, we are in need of a therapy that could ameliorate or even reverse the disease progression of CHF. Endogenous regeneration of the mammalian heart has been shown in the neonatal heart, and the discovery that it may still persist in adulthood sparked hope for novel cardioregenerative therapies. As the basis for cardiomyocyte renewal, multipotent cardiac stem/progenitor cells (CSCs) that reside in the heart have been shown to differentiate into cardiac myocytes, smooth muscle cells, and vascular endothelial cells. These CSCs do have the potential to actively regenerate the heart but clearly fail to do so after abundant and segmental loss of cells, such as what occurs with myocardial infarction. Therefore, it is vital to continue research for the most optimal therapy based on the use or in situ stimulation of these CSCs. In this review, we discuss the current status of the cardioregenerative field. In particular, we summarize the current knowledge of CSCs as the regenerative substrate in the adult heart and their use in preclinical and clinical studies to repair the injured myocardium.