Cycling Werner's syndrome fibroblasts display calcium-dependent potassium currents

Characterization of cellular senescence mechanisms in human corneal endothelial cells

The human cornea is a tri-laminar structure composed of several cell types with substantial mitotic potential. Age-related changes in the cornea are associated with declining visual acuity and the onset of overt age-related corneal diseases. Corneal transplantation is commonly used to restore vision in patients with damaged or diseased corneas. However, the supply of donor tissue is limited, and thus there is considerable interest in the development of tissue-engineered alternatives. A major obstacle to these approaches is the short replicative lifespan of primary human corneal endothelial cells (HCEC). Accordingly, a comprehensive investigation of the signalling pathways and mechanisms underpinning proliferative lifespan and senescence in HCEC was undertaken. The effects of exogenous human telomerase reverse transcriptase expression, p53 knockdown, disruption of the pRb pathway by over-expression of CDK4 and reduced oxygen concentration on the lifespan of primary HCEC were evaluated. We provide proof-of-principle that forced expression of telomerase, when combined with either p53 knockdown or CDK4 over-expression, is sufficient to produce immortalized HCEC lines. The resultant cell lines express an HCEC-specific transcriptional fingerprint, and retain expression of the corneal endothelial temperature-sensitive potassium channel, suggesting that significant dedifferentiation does not occur as a result of these modes of immortalization. Exploiting these insights into proliferative lifespan barriers in HCEC will underpin the development of novel strategies for cell-based therapies in the human cornea.

A cell kinetic analysis of human umbilical vein endothelial cells

Cultures of normal human cells 'age' and become senescent in vitro due to a continuously declining mitotic fraction. Although endothelial cells represent a tissue of major relevance in the development of age-related vascular disease, the rate at which these cells senesce has never been systematically measured in culture. Accordingly the population kinetics of human vascular endothelial cells (HUVECs) serially passaged in vitro has been studied in order to determine (i) the rate of decline in the growth fraction; (ii) the rate of increase of the senescent fraction and (iii) the relationship between changes in these parameters and the baseline rate of apoptosis. Immunocytochemical visualisation of the growth fraction using antisera to the proliferation marker pKi67 showed a rate of decline in the growth fraction of 4.43+/-0.31% per population doubling. This was not accompanied by any change in cell cycle time as assessed using time lapse video microscopy. The number of senescent cells within the population increased at a rate of 6.47+/-0.3% as assessed by senescence associated beta-galactosidase activity. The baseline rate of apoptosis as measured by TUNEL remained essentially unchanged (0.31+/-0.07%) during this process. These data show (i) that senescence and apoptosis are unrelated processes in HUVEC and (ii) that senescent cells rapidly and progressively accumulate in dividing populations of endothelial cells. The physiological relevance of these observations is discussed.

Fibroblasts cultured from venous ulcers display cellular characteristics of senescence

PURPOSE

A well-recognized characteristic of venous ulcers is impaired healing. Fibroblasts cultured from venous ulcers (wound-fb) have been shown to have reduced growth rates and are larger than normal fibroblasts (normal-fb) from the ipsilateral limb. Reduced growth capacity and morphologic changes are 2 well-known traits of cellular senescence. Other molecular changes are overexpression of matrix proteins, such as cellular fibronectin (cFN), and enhanced activity of beta-galactosidase at pH of 6.0 (senescence associated beta-Gal, or SA-beta-Gal). Senescence, an irreversible arrest of cell proliferation with maintenance of metabolic functions, may represent in vivo aging and thus may be related to impaired healing.

METHODS

Cultured normal-fb and wound-fb from 7 venous ulcer patients (average age, 51 years) were obtained by taking punch biopsies of the perimeter of the ulcer and from the ipsilateral thigh of the same patient. Growth rates, SA-beta-Gal activity, and level of cFN protein (immunoblot) and message (Northern blot) were measured.

RESULTS

In all patients, wound-fb growth rates were significantly lower than those of normal-fb (P =.006). A higher percentage of SA-beta-Gal positive cells were found in all wound-fb (average, 6.3% vs. 0.21%; P =.016). The level of cFN, was consistently higher in all wound-fb tested. Also, in 4 patients, the level of cFN messenger RNA (mRNA) was increased.

CONCLUSION

Fibroblasts cultured from venous ulcers exhibited characteristics associated with senescent cells. Accumulation of senescent cell in ulcer environment may be associated with impaired healing.

Progeroid syndromes: probing the molecular basis of aging?

A valid method of studying age related degenerative pathologies is to study human genetic diseases that appear to accelerate many, though not necessarily all, features of the aging process. Such diseases are described as progeroid syndromes because of their possible relevance to many aspects of aging and age related disease. This article describes the recent progress made at the cellular and molecular levels in understanding the pathogenesis of one of the best characterised of these disorders, Werner's syndrome. These observations are related to some of the less well characterised progeroid syndromes within the context of the cell senescence hypothesis of aging, a theory formulated to explain the aging of regenerative tissue in normal individuals.