Human microvascular endothelial cells: Coordinate induction of morphologic differentiation and twofold extension of life span

Summary Human microvascular endothelial cells (HMVEC) from adult adipose tissue were cultured in MCDB 131 medium supplemented with 10% fetal bovine serum. Under these conditions, HMVEC from seven different donors had finite proliferative life spans ranging from 14.5 to 23.5 population doublings (PD), with a mean life span of 19 PD. Addition of 10% conditioned medium from activated human leukocyte cultures (BM Condimed^?) extended the life span of HMVEC to 31 to 41 PD, with a mean life span of 37 PD. At the end of lifespan, HMVEC cultures both with and without BM Condimed had very low labeling indices (0 to 5% [³H]thymidine labeled nuclei) and consisted of enlarged cells. However, the morphologies of the two types of HMVEC cultures were very different. Untreated HMVEC were polygonal endothelial cells that formed cobblestonelike monolayers with no cell overlapping. In contrast, BM Condimed-treated HMVEC were more elongated, less regularly shaped cells that were not strictly inhibited from overlapping. When old, these cells accumulated numerous vacuoles. The BM Condimed-treated HMVEC expressed Factor VIII antigen, which confirms their identity as endothelial cells. These cells reverted rapidly to the polygonal morphology of untreated HMVEC when they were removed from BM Condimed. Likewise, their proliferative capacity was not extended further once BM condimed was removed. These results suggest that HMVEC can exist in two distinct morphologic states in which the cells have different finite proliferative life spans. This work was supported by grants AG00947 and AG04811 from the National Institute on Aging, Bethesda, MD.     

Are skin senescence and immunosenescence linked within individuals?

With advancing age, many organs exhibit functional deterioration. The age‐associated accumulation of senescent cells is believed to represent one factor contributing to this phenomenon. While senescent cells are found in several different organ systems, it is not known whether they arise independently in each organ system or whether their prevalence within an individual reflects that individual's intrinsic aging process. To address this question, we studied senescence in two different organ systems in humans, namely skin and T cells in 80 middle‐aged and older individuals from the Leiden Longevity Study. Epidermal p16INK4a positivity was associated with neither CD4⁺ nor CD8⁺ T‐cell immunosenescence phenotype composites (i.e., end‐stage differentiated/senescent T cells, including CD45RA⁺CCR7^‐CD28^‐CD27^‐CD57⁺KLRG1⁺ T cells). Dermal p16INK4a positivity was significantly associated with the CD4⁺, but not with the CD8⁺ immunosenescence composite. We therefore conclude that there is limited evidence for a link between skin senescence and immunosenescence within individuals.     

Age-associated increase in heterochromatic marks in murine and primate tissues

Chromatin is highly dynamic and subject to extensive remodeling under many physiologic conditions. Changes in chromatin that occur during the aging process are poorly documented and understood in higher organisms, such as mammals. We developed an immunofluorescence assay to quantitatively detect, at the single cell level, changes in the nuclear content of chromatin-associated proteins. We found increased levels of the heterochromatin-associated proteins histone macro H2A (mH2A) and heterochromatin protein 1 beta (HP1β) in human fibroblasts during replicative senescence in culture, and for the first time, an age-associated increase in these heterochromatin marks in several tissues of mice and primates. Mouse lung was characterized by monophasic mH2A expression histograms at both ages, and an increase in mean staining intensity at old age. In the mouse liver, we observed increased age-associated localization of mH2A to regions of pericentromeric heterochromatin. In the skeletal muscle, we found two populations of cells with either low or high mH2A levels. This pattern of expression was similar in mouse and baboon, and showed a clear increase in the proportion of nuclei with high mH2A levels in older animals. The frequencies of cells displaying evidence of increased heterochromatinization are too high to be readily accounted for by replicative or oncogene-induced cellular senescence, and are prominently found in terminally differentiated, postmitotic tissues that are not conventionally thought to be susceptible to senescence. Our findings distinguish specific chromatin states in individual cells of mammalian tissues, and provide a foundation to investigate further the progressive epigenetic changes that occur during aging.     

Death by transposition – the enemy within?

Here we present and develop the hypothesis that the derepression of endogenous retrotransposable elements (RTEs) – “genomic parasites” – is an important and hitherto under‐unexplored molecular aging process that can potentially occur in most tissues. We further envision that the activation and continued presence of retrotransposition contribute to age‐associated tissue degeneration and pathology. Chromatin is a complex and dynamic structure that needs to be maintained in a functional state throughout our lifetime. Studies of diverse species have revealed that chromatin undergoes extensive rearrangements during aging. Cellular senescence, an important component of mammalian aging, has recently been associated with decreased heterochromatinization of normally silenced regions of the genome. These changes lead to the expression of RTEs, culminating in their transposition. RTEs are common in all kingdoms of life, and comprise close to 50% of mammalian genomes. They are tightly controlled, as their activity is highly destabilizing and mutagenic to their resident genomes.     

The survey on cellular and tissue-engineered therapies in Europe and neighboring Eurasian countries in 2014 and 2015

Background aims

With the support of five established scientific organizations, this report, the seventh of its kind, describes activity in Europe for the years 2014 and 2015 in the area of cellular and tissue-engineered therapies, excluding hematopoietic stem cell (HSC) treatments for the reconstitution of hematopoiesis.