The Role of Cardiac Side Population Cells in Cardiac Regeneration

The heart has a limited ability to regenerate. It is important to identify therapeutic strategies that enhance cardiac regeneration in order to replace cardiomyocytes lost during the progression of heart failure. Cardiac progenitor cells are interesting targets for new regenerative therapies because they are self-renewing, multipotent cells located in the heart. Cardiac side population cells (cSPCs), the first cardiac progenitor cells identified in the adult heart, have the ability to differentiate into cardiomyocytes, endothelial cells, smooth muscle cells and fibroblasts. They become activated in response to cardiac injury and transplantation of cSPCs into the injured heart improves cardiac function. In this review, we will discuss the current literature on the progenitor cell properties and therapeutic potential of cSPCs. This body of work demonstrates the great promise cSPCs hold as targets for new regenerative strategies

Polymorphisms in the RAS and cardiac function

Since the discovery of the polymorphism in the angiotensin converting enzyme (ACE) and the consequences of this polymorphism on the activity levels of the enzyme, numerous association studies have been performed. However, these investigations do not often adhere to the most stringent criteria for such studies. The initial study reporting a positive association of the ACE polymorphism and myocardial infarction showed an increased risk of the DD genotype. This initial association was eventually refuted by a large, well conducted association study, which found a risk ratio of 1.02 after combining their own data with all published data. Although such large, well conducted association studies have not been performed in left ventricular (LV) hypertrophy, the association between DD genotype and hypertrophy is more convincing with a 192% excess risk of LV hypertrophy in untreated hypertensives. The role of ACE genotype in LV growth is well established, especially in athletes. In heart failure, large studies or meta-analyses have not been performed, because most studies have selected different end-points. This hampers a proper meta-analysis of the results obtained in associations with heart failure. As most association studies do not fulfill the criteria for good association studies and use too small sample sizes, it remains important to perform a meta-analysis to add meaning to the results of such studies. Above all, it is important to obey the rules set for association studies, large sample size, small P values, report associations that make biological sense and alleles that affect the gene product in a physiologically meaningful way. (C) 2003 Elsevier Science Ltd. All rights reserved

Parsing the roles of the transcription factors GATA-4 and GATA-6 in the adult cardiac hypertrophic response.

The transcriptional code that programs cardiac hypertrophy involves the zinc finger-containing DNA binding factors GATA-4 and GATA-6, both of which are required to mount a hypertrophic response of the adult heart. Here we performed conditional gene deletion of Gata4 or Gata6 in the mouse heart in conjunction with reciprocal gene replacement using a transgene encoding either GATA-4 or GATA-6 in the heart as a means of parsing dosage effects of GATA-4 and GATA-6 versus unique functional roles. We determined that GATA-4 and GATA-6 play a redundant and dosage-sensitive role in programming the hypertrophic growth response of the heart following pressure overload stimulation. However, non-redundant functions were identified in allowing the heart to compensate and resist heart failure after pressure overload stimulation, as neither Gata4 nor Gata6 deletion was fully rescued by expression of the reciprocal transgene. For example, only Gata4 heart-specific deletion blocked the neoangiogenic response to pressure overload stimulation. Gene expression profiling from hearts of these gene-deleted mice showed both overlapping and unique transcriptional codes, which is presented. These results indicate that GATA-4 and GATA-6 play a dosage-dependent and redundant role in programming cardiac hypertrophy, but that each has a more complex role in maintaining cardiac homeostasis and resistance to heart failure following injury that cannot be compensated by the other

Cardiac-specific deletion of <i>Gata4</i> but not <i>Gata6</i> prevents compensatory angiogenesis in the hearts of mice.

<p>The graph shows immunohistological quantitation of capillaries in the left ventricle normalized to surrounding cardiomyocytes in the indicated groups of mice. TAC was performed for 2 weeks. Mice were 10–12 weeks of age at harvesting. Hearts from at least 4 mice were analyzed in each group. *P<0.05 versus <i>Gata6^fl/fl</i> or <i>Gata4^fl/fl</i> sham.</p

qRT-PCR confirmation of differentially regulated genes.

<p>Adult heart mRNA was collected from the indicated lines of adult mice and subjected to qRT-PCR to analyze for differences in gene expression to verify or extend the Affymetrix results shown in Supplemental <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084591#pone-0084591-t001" target="_blank">Table 1</a>. Gene names are shown in the left column. Values are set relative to expression in <i>Gata6^fl/fl</i> or <i>Gata4^fl/fl</i> controls.</p

Differentially regulated genes from microarray.

<p>Adult heart mRNA was collected from <i>Gata6^{fl/fl-βMHC-cre}</i> mice and compared against mRNA from <i>Gata6^fl/fl</i> to generate Affymetrix expression arrays of genes that were specifically changed in with deletion of <i>Gata6</i>. And identical protocol was used to analyze genes changed with deletion of <i>Gata4</i> from the heart. Afterwards the two arrays sets were cross compared to examine genes that might be more specific to GATA-4 or GATA-6 regulation, which is represented as the column “difference” showing normalized expression results. The values represent the difference between normalized GATA-4 expression over normalized GATA-6 expression, both of which are corrected to the common cre control and each respective floxed line control. The negative numbers represent downregulated genes. Gene names are shown in the left column and protein names are shown in the very next column.</p

GATA-4 and GATA-6 play redundant roles in programming cardiac hypertrophy but not in adapting functional compensation.

<p>A, Ventricular weight to body weight (VW/BW) in the indicated genotypes of mice at 10–12 weeks of age following 2 weeks of TAC stimulation. The number of mice analyzed is shown in each bar of the graph. *P<0.05 versus <i>Gata4^fl/+ Gata6^fl/+</i>; #P<0.05 versus <i>Gata4^fl/+ Gata6^fl/+</i> with the βMHC-cre transgene. B, Fractional shortening (FS%) from the indicated mice at 10–12 weeks of age following sham or 2 weeks of TAC stimulation. The number of mice analyzed is shown in each bar of the graph. *P<0.05 versus <i>Gata4^fl/+ Gata6^fl/+</i> with the βMHC-cre transgene. C, VW/BW in the indicated groups of mice after 2 weeks of TAC stimulation at 10–12 weeks of age. The number of mice analyzed is shown in each bar of the graph. *P<0.05 versus <i>Gata6^fl/fl</i> tTA transgene; #P<0.05 versus <i>Gata6^{fl/fl-βMHC-cre}</i> tTA transgene. Abbreviations; tTA-G4, tetracycline transactivator transgene with the GATA-4 (G4) transgene; tTA-G6, tetracycline transactivator transgene with the GATA-6 (G6) transgene. D, Fractional shortening to measure ventricular performance of the same mice described in “C”. *P<0.05 versus <i>Gata6^fl/fl</i> tTA transgene; ^†P<0.05 versus <i>Gata6^{fl/fl-βMHC-cre}</i> tTA transgene; #P<0.05 versus <i>Gata6^{fl/fl-βMHC-cre}</i> tTA transgene or <i>Gata6^{fl/fl-βMHC-cre}</i> tTA transgene with GATA-4 transgene. E, F, Echocardiography measured left ventricular end diastolic dimension (LVED) and septal thickness in hearts of the indicated groups of mice after 2 weeks of TAC. G, Fractional shortening in <i>Gata4</i> heart-specific, deleted mice with the additional transgenes shown after 2 weeks of TAC stimulation. Number of mice analyzed is shown in the bars. *P<0.05 versus <i>Gata4^fl/fl</i> tTA transgene; #P<0.05 versus <i>Gata4^{fl/fl-βMHC-cre}</i> tTA transgene with the GATA-6 transgene. H, I, Western blot analysis for GATA-4 (G4) or GATA-6 (G6) protein from the hearts of the indicated mice. A non-specific (n.s.) band from each of the western blots was used to show equal loading and running conditions.</p