Contractile forces generated by striae distensae fibroblasts embedded in collagen lattices.

Striae distensae are characterized by linear, smooth bands of atrophic-appearing skin that are reddish at first and finally white. They are due to stretching of the skin, as in rapid weight gain, or mechanical stress, as in weight lifting. The pathogenesis of striae distensae is unknown but probably relates to changes in the fibroblast phenotype. In order to characterize striae distensae fibroblasts, alpha-smooth muscle actin expression and contractile forces were studied. Five healthy women with early erythematous striae and five healthy women with older striae were selected. Paired biopsies were taken from the center of lesional striae and adjacent normal skin. Fibroblasts were obtained by an explant technique and expanded in vitro in Dulbecco's modified Eagle's medium. Contractile forces generated by fibroblasts in collagen lattices were measured with the Glasbox device developed in our laboratory. Alpha-smooth muscle actin expression was studied by immunofluorescence labeling of cells and by flow cytometry. Fibroblasts from early striae distensae were the richest cells in alpha-smooth muscle actin filaments and generated the highest contractile forces. Their peak contractile force was 26% greater than normal fibroblasts. There was a 150% higher level of alpha-smooth muscle actin content in fibroblasts from early striae distensae compared with fibroblasts from normal skin. In contrast, there was no significant difference in force generation between old striae fibroblasts and normal fibroblasts with cells expressing no alpha-smooth muscle actin. The contractile properties of fibroblasts from striae distensae varies depending on the stage of the disease. In early striae distensae, fibroblasts acquire a more contractile phenotype, corresponding to that of myofibroblasts.

Indication of fibroblast apoptosis during the maturation of disc-shaped mechanically stressed collagen lattices.

Human dermal fibroblasts seeded in tense disc-shaped collagen gels organized gradually into a tissue composed of three distinct superimposed layers of cells: a basal layer of aligned myofibroblasts, a middle layer of unoriented fibroblasts, and an upper layer of myofibroblasts oriented orthogonally to the basal myofibroblasts. Confocal observation of alpha-smooth muscle actin (alpha-SMA) immunolabelling as a marker of myofibroblasts showed that the upper myofibroblasts disappeared during maturation of the lattices. Observation of morphological modifications of cells, typical chromatin condensation identified by Hoechst 33258 staining, and detection of ssDNA after formamide-induced denaturation suggested the involvement of apoptosis in myofibroblast disappearance. It is suggested that the model of disc-shaped stressed collagen lattice is thus able to mimic conditions in wound repair: on the one hand, wound contraction during which fibroblasts undergo mechanical stress and, on the other, apoptotic disappearance of cells at the end of tissue retraction.

Changes of peroxisomal fatty acid metabolism during cold acclimatization in hibernating jerboa (Jaculus orientalis).

Jerboa (Jaculus orientalis) is a deep hibernator originating from sub-desert highlands and represents an excellent model to help to understand the incidence of seasonal variations of food intake and of body as well as environmental temperatures on lipid metabolism. In jerboa, hibernation processes are characterized by changes in the size of mitochondria, the number of peroxisomes in liver and in the expression of enzymes linked to fatty acid metabolism. In liver and kidney, cold acclimatization shows an opposite effect on the activities of the mitochondrial acyl-CoA dehydrogenase (-50%) and the peroxisomal acyl-CoA oxidase (AOX) (+50%), while in brown and white adipose tissues, both activities are decreased down to 85%. These enzymes activities are subject to a strong induction in brown and in white adipose tissue (3.4- to 7.5-fold, respectively) during the hibernation period which is characterized by a low body temperature (around 10 degrees C) and by starvation. Expression level of AOX mRNA and protein are increased during both pre-hibernation and hibernation periods. Unexpectedly, treatment with ciprofibrate, a hypolipemic agent, deeply affects lipolysis in brown adipose tissue by increasing acyl-CoA dehydrogenase activity (3.4-fold), both AOX activity and mRNA levels (2.8- and 3.8-fold, respectively) during pre-hibernation. Therefore, during pre-hibernation acclimatization, there is a negative regulation of fatty acid degradation allowing to accumulate a lipid stock which is later degraded during the hibernation period (starvation) due to a positive regulation of enzymes providing the required energy for animal survival.

Germinal and non-germinal lines in the ovotestis of Helix aspersa: a survey.

The study of gonadal organogenesis and differentiation by means of light and electron microscopy suggested the following in Helix aspersa: (1) the distal parts of the acini have components of mesodermal origin, whereas the neck and efferent duct comprise ectodermal elements; (2) a segregation of a germinal line occurs early, during the embryonic life; (3) in juvenile and adult animals, male and female cells arise from a germinal ring located at the base of the acinar neck. Apart from developing oocytes, the epithelium lining the distal region of the acini consists of somatic cells (Sertoli and follicle cells).