A Novel Class of Human Cardiac Stem Cells

Abstract

Following the recognition that hematopoietic stem cells improve the outcome of myocardial infarction in animal models, bone marrow mononuclear cells, CD34-positive cells, and mesenchymal stromal cells have been introduced clinically. The intracoronary or intramyocardial injection of these cell classes has been shown to be safe and to produce a modest but significant enhancement in systolic function. However, the identification of resident cardiac stem cells in the human heart (hCSCs) has created great expectation concerning the potential implementation of this category of autologous cells for the management of the human disease. Although phase 1 clinical trials have been conducted with encouraging results, the search for the most powerful hCSC for myocardial regeneration is in its infancy. This manuscript discusses the efforts performed in our laboratory to characterize the critical biological variables that define the growth reserve of hCSCs. Based on the theory of the immortal DNA template, we propose that stem cells retaining the old DNA represent 1 of the most powerful cells for myocardial regeneration. Similarly, the expression of insulin-like growth factor-1 receptors in hCSCs recognizes a cell phenotype with superior replicating reserve. However, the impressive recovery in ventricular hemodynamics and anatomy mediated by clonal hCSCs carrying the "mother" DNA underscores the clinical relevance of this hCSC class for the treatment of human heart failure.

Figure 1

Schematic representation of DNA segregation with stem cell division. A, With asymmetric chromatid segregation, one dividing mother stem cell (DNA strands, blue) synthesizes new DNA (red) during S-phase. The two sets of chromosomes are separated in anaphase and then the two daughter stem cells are generated, one carrying only the mother DNA (blue) and the other only the newly-synthesized DNA (red). In each chromosome, the two sister chromatids are held together at their centromere (green dot). B, With symmetric chromatid segregation, one dividing mother stem cell (DNA strands, blue) synthesizes new DNA (red) during S-phase and generates two daughter stem cells, each carrying the mother DNA (blue) and the newly-synthesized DNA (red). (Adapted from Kajstura et al, Circ Res 2012). Ref 10

Figure 2

One grandparent stem cell (DNA strands, blue) entering the cell cycle synthesizes new DNA during S-phase, incorporating BrdU (red); two parent stem cells are formed, each carrying the unlabeled grandparent DNA (blue) and the BrdU-labeled newly-synthesized DNA (red). Subsequent division of each parent stem cell results in the generation of one daughter stem cell, carrying the old, unlabeled grandparent DNA (blue), and one daughter stem cell, carrying only the newly-synthesized, BrdU-labeled DNA. Newly-synthesized unlabeled DNA (black). (Adapted from Kajstura et al, Circ Res 2012).

Figure 3

Notch inhibition induces a dilated myopathy. A, Schematic representation of the interaction between Jagged1 and Notch1 within the cardiac stem cell niches. B, Fraction of Nkx2.5-positive CSCs in the absence (control) and presence of N1ICD overexpression (N1ICD). Results are means±SD. *P<0.05. C and D, B-mode and M-mode echocardiography of vehicle (left) and γ-secretase inhibitor–injected (right) mice. E and F, γ-secretase inhibition led to ventricular dilation, depressed fractional shortening and ejection fraction, and increased mortality. G, With respect to a control heart (left panel), ventricular dilation and wall thinning are apparent in γ-secretase inhibitor–treated mice (central and right panels). H, Effects of γ-secretase inhibition on cardiac anatomy. Results are means±SD. *P<0.05.(Adapted from Urbanek et al, Circ Res 2010). Ref 52

Figure 3

Notch inhibition induces a dilated myopathy. A, Schematic representation of the interaction between Jagged1 and Notch1 within the cardiac stem cell niches. B, Fraction of Nkx2.5-positive CSCs in the absence (control) and presence of N1ICD overexpression (N1ICD). Results are means±SD. *P<0.05. C and D, B-mode and M-mode echocardiography of vehicle (left) and γ-secretase inhibitor–injected (right) mice. E and F, γ-secretase inhibition led to ventricular dilation, depressed fractional shortening and ejection fraction, and increased mortality. G, With respect to a control heart (left panel), ventricular dilation and wall thinning are apparent in γ-secretase inhibitor–treated mice (central and right panels). H, Effects of γ-secretase inhibition on cardiac anatomy. Results are means±SD. *P<0.05.(Adapted from Urbanek et al, Circ Res 2010). Ref 52

Figure 4

Schematic representation of clonal assay. Unlabeled grandparent human CSCs (hCSCs; DNA strands, blue), undergoing cell division in the presence of BrdU, generate parent hCSCs which incorporate the halogenated nucleotide in the newly synthesized DNA (red). BrdU-tagged parent hCSCs (one DNA strand, red) can divide by non-random and random segregation of chromatids, giving rise to two types of clones: one contains only one BrdU-positive hCSC (one red nucleus) and the other is formed by hCSCs all BrdU-positive (all red nuclei). (Adapted from Kajstura et al, Circ Res 2012).

Figure 5

Growth characteristics of hCSCs. A, Clonal growth and population doubling time of hCSCs dividing by asymmetrical and symmetrical chromatid segregation, respectively. B, Rate of apoptosis and senescence in hCSC classes. Results are means±SD. *P<0.05 versus new DNA. (Adapted from Kajstura et al, Circ Res 2012).

Figure 6

Left-right dynein motor protein (LRD). Representative tracings of transcript for LRD in hCSCs and human myocardium (hMyo). PCR products had the correct molecular size. (Adapted from Kajstura et al, Circ Res 2012).

Figure 7

Growth properties of hCSCs. A, Clones derived from hCSCs carrying the old (red) and new (blue) DNA in various patients. Linear relationship between age and number of clones formed by hCSCs carrying the old (red) and new (blue) DNA. B, Distribution of telomere length in hCSC subsets; in hearts 46 to 83 years old (y), telomere length of hCSCs carrying the old DNA is shifted toward higher values. C, Telomere length decreases with age only in hCSCs carrying the new DNA. Telomerase activity in hCSC subsets measured by qPCR. Data are presented as individual values or as mean±SD. (Adapted from Kajstura et al, Circ Res 2012).

Figure 7

Growth properties of hCSCs. A, Clones derived from hCSCs carrying the old (red) and new (blue) DNA in various patients. Linear relationship between age and number of clones formed by hCSCs carrying the old (red) and new (blue) DNA. B, Distribution of telomere length in hCSC subsets; in hearts 46 to 83 years old (y), telomere length of hCSCs carrying the old DNA is shifted toward higher values. C, Telomere length decreases with age only in hCSCs carrying the new DNA. Telomerase activity in hCSC subsets measured by qPCR. Data are presented as individual values or as mean±SD. (Adapted from Kajstura et al, Circ Res 2012).

Figure 7

Growth properties of hCSCs. A, Clones derived from hCSCs carrying the old (red) and new (blue) DNA in various patients. Linear relationship between age and number of clones formed by hCSCs carrying the old (red) and new (blue) DNA. B, Distribution of telomere length in hCSC subsets; in hearts 46 to 83 years old (y), telomere length of hCSCs carrying the old DNA is shifted toward higher values. C, Telomere length decreases with age only in hCSCs carrying the new DNA. Telomerase activity in hCSC subsets measured by qPCR. Data are presented as individual values or as mean±SD. (Adapted from Kajstura et al, Circ Res 2012).

Figure 8

Effects of age and diabetes on hCSCs. A, Relationships of aging to receptor and ligand expression in hCSCs. B, Diabetes affected further IGF-2R and AT1R expression. *P<0.05 vs. non-diabetic patients. C, hCSCs with old DNA have a greater impact on left ventricular end-diastolic pressure (LVEDP), LV systolic pressure (LVSP), LV developed pressure (LVDP), positive and negative dP/dt, and calculated diastolic wall stress than hCSCs carrying the new DNA. (A and B, adapted from D'Amario et al, Circ Res 2011; C, adapted from Kajstura et al, Circ Res 2012)

Figure 8

Effects of age and diabetes on hCSCs. A, Relationships of aging to receptor and ligand expression in hCSCs. B, Diabetes affected further IGF-2R and AT1R expression. *P<0.05 vs. non-diabetic patients. C, hCSCs with old DNA have a greater impact on left ventricular end-diastolic pressure (LVEDP), LV systolic pressure (LVSP), LV developed pressure (LVDP), positive and negative dP/dt, and calculated diastolic wall stress than hCSCs carrying the new DNA. (A and B, adapted from D'Amario et al, Circ Res 2011; C, adapted from Kajstura et al, Circ Res 2012)