M.F.M. van Oosterhout

Suppression of physiological cardiomyocyte proliferation in the rat pup after neonatal glucocorticosteroid treatment

AbstractBackgroundGlucocorticosteroids (mostly dexamethasone) are widely used to prevent chronic lung disease in premature infants. Neonatal rats treated with dexamethasone have been shown to have reduced cardiac mass and cardiomyocyte hypertrophy, suggesting a lower number of cardiomyocytes at adult age, and a severely reduced life expectancy. In the present study we tested the hypothesis that a lower number of cardiomyocytes in later life is caused by a reduced cardiomyocyte proliferation and/or by early cell death (apoptosis).Methods and resultsRat pups received dexamethasone or saline control on day 1, 2 and 3 and were sacrificed at day 0, 2, 4, 7 and 21. The cardiomyocytes of dexamethasone treated pups showed a reduced proliferation as indicated by a lower mitotic index and reduced number of Ki–67 positive cardiomyocytes on day 2 and 4 as compared to day 0 and day 7 and also as compared to the age–matched saline pups. On day 7 and day 21 the mitotic index was not different between groups. From day 2 onward up to day 21 dexamethasone treated pups showed a lower number of cardiomyocytes. The cardiomyocytes showed no signs (<<1%) of apoptosis (Caspase–3 and cleaved–PARP) in any group.ConclusionThe temporary suppression of cardiomyocyte hyperplasia found in dexamethasone treated pups eventually leads to a reduced number and hypertrophy of cardiomyocytes during adult life.

T cells in Cardiac Allograft Vasculopathy Are Skewed to Memory Th-1 Cells in the Presence of a Distinct Th-2 Population

Cardiac allograft vasculopathy (CAV) in heart transplantation (HTx) patients remains the major complication for long‐term survival, due to concentric neointima hyperplasia induced by infiltrating mononuclear cells (MNC). Previously, we showed that activated memory T‐helper‐1 (Th‐1) cells are the major component of infiltrating MNC in coronary arteries with CAV. In this study, a more detailed characterization of the MNC in human coronary arteries with CAV (n = 5) was performed and compared to coronary arteries without CAV (n = 5), by investigating MNC markers (CD1a, DRC‐1, CD3, CD20, CD27, CD28, CD56, CD68, CD69, FOXP3 and HLA‐DR), cytokines (IL‐1A, 2, 4, 10, 12B, IFN‐γ, and TGF‐β1), and chemokine receptors (CCR3, CCR4, CCR5, CCR7, CCR8, CXCR3 and CX3CR1) by immunohistochemical double‐labeling and quantitative PCR on mRNA isolated from laser microdissected layers of coronary arteries. T cells in the neointima and adventitia of CAV were skewed toward an activated memory Th‐1 phenotype, but in the presence of a distinct Th‐2 population. FOXP3 positive T cells were not detected and production of most cytokines was low or absent, except for IFN‐γ, and TGF‐β. This typical composition of T‐helper cells and especially production of IFN‐γ and TGF‐β may play an important role in the proliferative CAV reaction.

Stem cell-derived cardiomyocytes after bone marrow and heart transplantation

Cardiomyocytes are a stable cell population with only limited potential for renewal after injury. Tissue regeneration may be due to infiltration of stem cells, which differentiate into cardiomyocytes. We have analysed the influx of stem cells in the heart of patients who received either a gender-mismatched BMT (male donor to female recipient) or a gender-mismatched cardiac transplant (HTX; female donor to male recipient). The proportion of infiltrating cells was determined by Y-chromosome in situ hybridization combined with immunohistochemical cell characterization. In BM transplanted patients and in cardiac allotransplant recipients, cardiomyocytes of apparent BM origin were detected. The proportions were similar in both groups and amounted up to 1% of all cardiomyocytes. The number of stem cell-derived cardiomyocytes did not alter significantly in time, but were relatively high in cases where large numbers of BM-derived Y-chromosome-positive infiltrating inflammatory cells were present. The number of Y-chromosome-positive endothelial cells was small and present only in small blood vessels. The number of BM-derived cardiomyocytes in both BMT and HTX is not significantly different between the two types of transplantation and is at most 1%.