Early bilirubinemia after allogeneic stem cell transplantation - an endothelial complication

Hyperbilirubinemia occurs frequently after allogeneic stem cell transplantation. Causes include primary liver damage and endothelial complications as major contributors. Here, we have investigated the impact of early bilirubinemia (EB) on posttransplant outcomes. Maximum total bilirubin levels (days 0-28) were categorized using maximally selected log rank statistics to identify a cut off for the endpoint non-relapse mortality (NRM) in a training cohort of 873 patients. EB above this cut off was correlated with NRM and overall survival (OS) and with pre- and posttransplant Angiopoietin-2, interleukin (IL)18, CXCL8 and suppressor of tumorigenicity-2 (ST2) serum levels, and the endothelial activation and stress index (EASIX). Clinical correlations were validated in a sample of 388 patients transplanted in an independent institution. The EB cut off was determined at 3.6 mg/dL (61.6 mu M). EB predicted OS (HR 1.60, 95% CI 1.21-2.12, p < 0.001), and NRM (CSHR 2.14; 1.28-3.56, p = 0.004), also independent of typical endothelial complications such as veno-occlusive disease, refractory acute graft-versus-host disease, or transplant-associated microangiopathy. However, EB correlated with high Angiopoietin-2, EASIX-pre and EASIX-day 0, as well as increased levels of posttransplant CXCL8, IL18, and ST2. In summary, EB indicates a poor prognosis. The association of EB with endothelial biomarkers suggests an endothelial pathomechanism also for this posttransplant complication

Cardiomyogenesis in the adult human heart

Rationale: The ability of the human heart to regenerate large quantities of myocytes remains controversial, and the extent of myocyte renewal claimed by different laboratories varies from none to nearly 20% per year. Objective: To address this issue, we examined the percentage of myocytes, endothelial cells, and fibroblasts labeled by iododeoxyuridine in postmortem samples obtained from cancer patients who received the thymidine analog for therapeutic purposes. Additionally, the potential contribution of DNA repair, polyploidy, and cell fusion to the measurement of myocyte regeneration was determined. Methods and Results: The fraction of myocytes labeled by iododeoxyuridine ranged from 2.5% to 46%, and similar values were found in fibroblasts and endothelial cells. An average 22%, 20%, and 13% new myocytes, fibroblasts, and endothelial cells were generated per year, suggesting that the lifespan of these cells was approximately 4.5, 5, and 8 years, respectively. The newly formed cardiac cells showed a fully differentiated adult phenotype and did not express the senescence-associated protein p16(INK4a). Moreover, measurements by confocal microscopy and flow cytometry documented that the human heart is composed predominantly of myocytes with 2n diploid DNA content and that tetraploid and octaploid nuclei constitute only a small fraction of the parenchymal cell pool. Importantly, DNA repair, ploidy formation, and cell fusion were not implicated in the assessment of myocyte regeneration. Conclusions: Our findings indicate that the human heart has a significant growth reserve and replaces its myocyte and nonmyocyte compartment several times during the course of life

Spontaneous calcium oscillations regulate human cardiac progenitor cell growth

Rationale: The adult heart possesses a pool of progenitor cells stored in myocardial niches, but the mechanisms involved in the activation of this cell compartment are currently unknown. Objective: Ca(2+) promotes cell growth raising the possibility that changes in intracellular Ca(2+) initiate division of c-kit-positive human cardiac progenitor cells (hCPCs) and determine their fate. Methods and Results: Ca(2+) oscillations were identified in hCPCs and these events occurred independently from coupling with cardiomyocytes or the presence of extracellular Ca(2+). These findings were confirmed in the heart of transgenic mice in which enhanced green fluorescent protein was under the control of the c-kit promoter. Ca(2+) oscillations in hCPCs were regulated by the release of Ca(2+) from the endoplasmic reticulum through activation of inositol 1,4,5-triphosphate receptors (IP3Rs) and the reuptake of Ca(2+) by the sarco-/endoplasmic reticulum Ca(2+) pump (SERCA). IP3Rs and SERCA were highly expressed in hCPCs, whereas ryanodine receptors were not detected. Although Na(+)-Ca(2+) exchanger, store-operated Ca(2+) channels and plasma membrane Ca(2+) pump were present and functional in hCPCs, they had no direct effects on Ca(2+) oscillations. Conversely, Ca(2+) oscillations and their frequency markedly increased with ATP and histamine which activated purinoceptors and histamine-1 receptors highly expressed in hCPCs. Importantly, Ca(2+) oscillations in hCPCs were coupled with the entry of cells into the cell cycle and 5-bromodeoxyuridine incorporation. Induction of Ca(2+) oscillations in hCPCs before their intramyocardial delivery to infarcted hearts was associated with enhanced engraftment and expansion of these cells promoting the generation of a large myocyte progeny. Conclusion: IP3R-mediated Ca(2+) mobilization control hCPC growth and their regenerative potential. (Circ Res. 2009; 105: 764-774.

Myocyte Turnover in the Aging Human Heart

Rationale: The turnover of cardiomyocytes in the aging female and male heart is currently unknown, emphasizing the need to define human myocardial biology. Objective: The effects of age and gender on the magnitude of myocyte regeneration and the origin of newly formed cardiomyocytes were determined. Methods and Results: The interaction of myocyte replacement, cellular senescence, growth inhibition, and apoptosis was measured in normal female (n=32) and male (n=42) human hearts collected from patients 19 to 104 years of age who died from causes other than cardiovascular diseases. A progressive loss of telomeric DNA in human cardiac stem cells (hCSCs) occurs with aging and the newly formed cardiomyocytes inherit short telomeres and rapidly reach the senescent phenotype. Our data provide novel information on the superior ability of the female heart to sustain the multiple variables associated with the development of the senescent myopathy. At all ages, the female heart is equipped with a larger pool of functionally competent hCSCs and younger myocytes than the male myocardium. The replicative potential is higher and telomeres are longer in female hCSCs than in male hCSCs. In the female heart, myocyte turnover occurs at a rate of 10%, 14%, and 40% per year at 20, 60, and 100 years of age, respectively. Corresponding values in the male heart are 7%, 12%, and 32% per year, documenting that cardiomyogenesis involves a large and progressively increasing number of parenchymal cells with aging. From 20 to 100 years of age, the myocyte compartment is replaced 15 times in women and 11 times in men. Conclusions: The human heart is a highly dynamic organ regulated by a pool of resident hCSCs that modulate cardiac homeostasis and condition organ aging. (Circ Res. 2010;107:1374-1386.

Spontaneous calcium oscillations regulate human cardiac progenitor cell growth

RATIONALE: The adult heart possesses a pool of progenitor cells stored in myocardial niches but the mechanisms involved in the activation of this cell compartment are currently unknown. OBJECTIVE: Ca(2+) promotes cell growth raising the possibility that changes in intracellular Ca(2+) initiate division of c-kit-positive human cardiac progenitor cells (hCPCs) and determine their fate. METHODS AND RESULTS: Ca(2+) oscillations were identified in hCPCs and these events occurred independently from coupling with cardiomyocytes or the presence of extracellular Ca(2+). These findings were confirmed in the heart of transgenic mice in which EGFP was under the control of the c-kit-promoter. Ca(2+) oscillations in hCPCs were regulated by the release of Ca(2+) from the ER through activation of inositol 1,4,5-triphosphate receptors (IP3Rs) and the re-uptake of Ca(2+) by the sarco/endoplasmic reticulum Ca(2+) pump (SERCA). IP3Rs and SERCA were highly expressed in hCPCs while ryanodine receptors were not detected. Although Na(+)-Ca(2+) exchanger, store-operated Ca(2+)-channels and plasma membrane Ca(2+)-pump were present and functional in hCPCs, they had no direct effects on Ca(2+) oscillations. Conversely, Ca(2+) oscillations and their frequency markedly increased with ATP and histamine which activated purinoceptors and histamine-1 receptors highly expressed in hCPCs. Importantly, Ca(2+) oscillations in hCPCs were coupled with the entry of cells into the cell cycle and BrdUrd incorporation. Induction of Ca(2+) oscillations in hCPCs prior to their intramyocardial delivery to infarcted hearts was associated with enhanced engraftment and expansion of these cells promoting the generation of a large myocyte progeny. CONCLUSION: IP3R-mediated Ca(2+) mobilization control hCPC growth and their regenerative potential

MYOCYTE TURNOVER IN THE AGING HUMAN HEART.

Rationale: The turnover of cardiomyocytes in the aging female and male heart is currently unknown, emphasizing the need to define human myocardial biology. Objective: The effects of age and gender on the magnitude of myocyte regeneration and the origin of newly formed cardiomyocytes were determined. Methods and Results: The interaction of myocyte replacement, cellular senescence, growth inhibition, and apoptosis was measured in normal female (n=32) and male (n=42) human hearts collected from patients 19 to 104 years of age who died from causes other than cardiovascular diseases. A progressive loss of telomeric DNA in human cardiac stem cells (hCSCs) occurs with aging and the newly formed cardiomyocytes inherit short telomeres and rapidly reach the senescent phenotype. Our data provide novel information on the superior ability of the female heart to sustain the multiple variables associated with the development of the senescent myopathy. At all ages, the female heart is equipped with a larger pool of functionally competent hCSCs and younger myocytes than the male myocardium. The replicative potential is higher and telomeres are longer in female hCSCs than in male hCSCs. In the female heart, myocyte turnover occurs at a rate of 10%, 14%, and 40% per year at 20, 60, and 100 years of age, respectively. Corresponding values in the male heart are 7%, 12%, and 32% per year, documenting that cardiomyogenesis involves a large and progressively increasing number of parenchymal cells with aging. From 20 to 100 years of age, the myocyte compartment is replaced 15 times in women and 11 times in men. Conclusions: The human heart is a highly dynamic organ regulated by a pool of resident hCSCs that modulate cardiac homeostasis and condition organ aging. (Circ Res. 2010;107:1374-1386.