Adipose-derived stromal cells for osteoarticular repair: trophic function versus stem cell activity.

The identification of multipotent adipose-derived stromal cells (ASC) has raised hope that tissue regeneration approaches established with bone-marrow-derived stromal cells (BMSC) can be reproduced with a cell-type that is far more accessible in large quantities. Recent detailed comparisons, however, revealed subtle functional differences between ASC and BMSC, stressing the concept of a common mesenchymal progenitor existing in a perivascular niche across all tissues. Focussing on bone and cartilage repair, this review summarises recent in vitro and in vivo studies aiming towards tissue regeneration with ASC. Advantages of good accessibility, high yield and superior growth properties are counterbalanced by an inferiority of ASC to form ectopic bone and stimulate long-bone healing along with their less pronounced osteogenic and angiogenic gene expression signature. Hence, particular emphasis is placed on establishing whether stem cell activity of ASC is so far proven and relevant for successful osteochondral regeneration, or whether trophic activity may largely determine therapeutic outcome.

The matricellular protein periostin contributes to proper collagen function and is downregulated during skin aging.

BACKGROUND: Periostin is a secreted 90kDa matricellular protein, which is predominantly expressed in collagen-rich tissues. Collagen is the most abundant protein in mammals and has great tensile strength. Recent investigations have shown that periostin influences collagen fibrillogenesis and biomechanical properties of murine connective tissues. OBJECTIVE: We investigated the function of periostin concerning collagen homeostasis during intrinsic and extrinsic skin aging. For this purpose, human skin samples of young and old donors as well as samples of photoaged and sun-protected skin areas were analyzed for periostin expression. Using in vitro models, we determined the cell types responsible for periostin expression and performed functional analyses with periostin knockdown cells. METHODS: TaqMan Real-Time PCR, UV irradiation, knockdown experiments, immunostaining, electron microscopy, collagen degradation assay, collagen crosslink analysis. RESULTS: Periostin expression is highest in the papillary dermis and downregulated during skin aging. Fibroblasts and non-follicular skin derived precursors were identified as main source for periostin expression in human skin. Periostin knockdown in fibroblasts has no effect on collagen expression, but results in an increased fibril diameter and aberrant collagen structure. This leads to an increased susceptibility of collagen toward proteases, whereas recombinant periostin protects collagen fibrils from degradation. CONCLUSION: Our data show that periostin plays an important role for proper collagen assembly and homeostasis. During skin aging periostin expression decreases and contributes to the phenotype of aged skin.

Quantification of cyclobutane pyrimidine dimers in human epidermal stem cells.

The common procedures that are used to quantify cyclobutane pyrimidine dimers (CPD) comprise the extraction of cellular DNA followed by the detection of this nucleic acid modification by immunoblotting or electrophoretic methods. Consequently, these approaches provide an averaged damage intensity value of a whole population of cells and are not applicable to studies where a small subgroup such as somatic stem cells are intended to be investigated and the individual cellular damage is of interest. Here, we describe a strategy to isolate epidermal stem cells from minimum human epidermis samples and a subsequent immunocytochemical quantification of cellular CPDs. Besides the determination of the DNA damage status, this technique allows for the examination of cellular CPD intensity distributions.

Structural changes in spruce and fir needles.

Needles from spruce and fir trees were analyzed for histological changes induced by long-term exposure in open-top chambers to SO(2) and/or O(3) combined with acid rain. Light and electron microscopical evaluation revealed initial structural changes in the vascular bundle of fir needles, with an increased number of crushed sieve cells in the phloem. In addition the walls of young, adaxial sieve cells lacked the typical thickening usually observed in naturally aged needles. These findings may indicate restricted assimilate translocation. The presence of SO(2) in any treatment led to thylakoidal swellings and membrane reductions in the chloroplasts of mesophyll cells near the vascular bundle. This damage pattern resembled alterations caused by nutrient deficiency rather than by the direct action of gaseous pollutants. In general, fir appears to be more sensitive to environmental stress than spruce; this substantiates the findings of previous studies.