Heat shock induces apoptosis in human embryonic stem cells but a premature senescence phenotype in their differentiated progeny

Embryonic stem cells (ESC) are able to self-renew and to differentiate into any cell type. To escape error transmission to future cell progeny, ESC require robust mechanisms to ensure genomic stability. It was stated that stress defense of mouse and human ESC against oxidative stress and irradiation is superior compared with differentiated cells. Here, we investigated heat shock response of human ESC (hESC) and their differentiated progeny. Fibroblast-like cells were generated by spontaneous hESC differentiation via embryoid bodies. Like normal human diploid fibroblasts, these cells have a finite lifespan in culture, undergo replicative senescence and die. We found that sublethal heat shock affected survival of both cell types, but in hESC it induced apoptosis, whereas in differentiated cells it produced cell cycle arrest and premature senescence phenotype. Heat shock survived hESC and differentiated cells restored the properties of initial cells. Heated hESC progeny exhibited pluripotent markers and the capacity to differentiate into the cells of three germ layers. Fibroblast-like cells resisted heat shock, proliferated for a limited number of passages and entered replicative senescence as unheated parental cells. Taken together, these results show for the first time that both hESC and their differentiated derivatives are sensitive to heat shock, but the mechanisms of their stress response are different: hESC undergo apoptosis, whereas differentiated cells under the same conditions exhibit stress-induced premature senescence (SIPS) phenotype. Both cell types that survived sublethal heat shock sustain parental cell properties.     

Effect of synthetic polycation polyallylamine on adhesion and viability of CHL V-79 RJK Chinese hamster fibroblasts with various heat resistance

The effects of synthetic polycation polyallylamine (PAA) on the adhesion of CHL V-79 RJK fibroblasts and CHL V-79 RJK40 cells resistant to 40°C and the attachment of these cells to polycation immobilized on a polystyrene surface have been studied. We also investigated PAA cytotoxicity. It was shown that cell adhesion on polystyrene plastic coated with PAA depended on the PAA dose and did not depend on the heat resistance of the cells. The effect of PAA on cell adhesion to uncoated polystyrene surface after cell exposure to PAA depended not only on the polycation concentration but also on cell heat resistance. Pretreatment of cells with nontoxic concentrations of PAA inhibited CHL V-79 RJK cell adhesion and did not change adhesive properties of thermotolerant cells. PAA is toxic for CHL V-79 RJK and CHL V-79 RJK40 cells only at concentration of 100 μg/ml (MTT assay). PAA-induced acute toxicity was accompanied by necrotic-like cell death. Possible mechanisms of the PAA effect on the behavior of cells with different metabolic characteristics defined by heat resistance are discussed.     

Changes in the mitotic activity of the corneal epithelium of white rats following coolong of the animals at different times of the day]

A study was made of the influence of moderate hypothermia on the mitotic activity of albino rat corneal epithelium. The animals were cooled by the contact method for one hour to 28 degrees C; such procedure was conducted at 6 a.m., at noon, and at 6 p.m.; the epithelial reaction to cooling proved to depend on the time, the greatest suppression of mitotic activity (14-fold) occurring at daytime 3 hours after the cooling. A tendency to normalization of cell division was observed 6 and 12 hours after the cooling. The number of mitoses decreased 3 hours after the evening cooling, no changes in the mitotic activity in 3 and 6 hours after the morning cooling; cell division was found to be suppressed in 12 hours.     

Prognostic significance of lysosomal cysteine proteases in the estimation of the effectiveness of the antitumor therapy

The influence of the antitumor drugs, cyclophosphamide (CPA) and nitrosomethylurea (NMU) on the activity of lysosomal cysteine proteases cathepsin B and L in tumor tissue has been investigated using CPA-sensitive (LS) and CPA-resistant mouse lymphosarcomas (RLS). (These drugs exhibit high and low antitumor efficiency towards LS and RLS mouse lymphosarcomas, respectively). Regression or reduction in the growth rate of LS and RLS lymphosarcomas caused by CPA or NMU administration was accompanied by the increase in the activity of cysteine proteases cathepsin B and L in the tumor tissue. The increase of cathepsin B and L activity in tumor tissue correlated with the therapeutic effect of these drugs. Data obtained suggest that activity of cathepsin B and L in tumor tissue has a prognostic significance for the estimation of the effectiveness of antitumor therapy.     

Effect of proprioceptive and visual stimulation on brain stem auditory evoked potentials in the cat and in man

Proprioceptive effect on the activity of different levels of the auditory system was studied in cats under Nembutal anaesthesia and in humans, by means of recording brain stem auditory evoked potentials - BAEPs (in response to cliks), whose consecutive waves correspond to successive levels of the auditory system. BAEPs were compared when the head was in a straight position and when it was turned 45 degrees to one side. The turns elicited changes in amplitudes and latencies of all BAEP waves similarly in cats and humans but in different combinations and in different directions, which points to plurality and heterogeneity of proprioceptive effects at different auditory levels. Analogous effect on BAEPs was produced by photic stimulation - illumination of one eye in cats and of the experimental chamber in humans. The character of the effects suggests participation of the activity of descending auditory paths and the cerebellum.