Basal keratinocytes

A single application of lauroyl peroxide to mouse skin induced mild hyperplasia and a temporary increase in dark basal keratinocytes. No major inflammatory or vascular change was noted (lARC, 1985). 

The mode of action of glycerol both on SC hydration and epidermal barrier function seems to be related to the aquaporin-3 (AQP3) channel. The basal layer of epidermal keratinocytes contains AQP3, a small membrane protein that functions as a facilitated transporter of water and glycerol.11 Glycerol is transported very slowly into the epidermis and thus its transport rate is sensitive to the intrinsic glycerol permeability of the basal keratinocyte layer. 

Hyaluronan is most prominent in the upper spinous and granular layers of the epidermis, where most of it is extracellular. The basal layer has HA, but it is predominantly intracellular, and is not easily leeched out during aqueous fixation. Presumably, basal keratinocyte HA is involved in cell cycling events, while the secreted HA in the upper outer layers of the epidermis are mechanisms for disassociation and eventual sloughing of cells. 

Cultures of isolated keratinocytes have facilitated the study of epithelial HA metabolism. Basal keratinocytes synthesize copious quantities of HA. When Ca++ of the culture medium is increased, from 0.05 to 1.20 mM, these cells begin to differentiate, HA synthesis levels drop,148 and there is an onset of hyaluronidase activity.149 This increase in calcium that appears to simulate in culture the natural in situ differentiation of basal keratinocytes parallels the increasing calcium gradient observed in the epidermis. There may be intracellular stores of calcium that are released as keratinocytes mature. 

The epidermis consists of several cell layers beginning with a layer of viable basal keratinocytes that differentiate into a cornified nonviable layer of squamous epithelium that covers the surface (see Figure 3.8). The various... 

A 68-year-old woman developed marked and persistent periocular swelling after infusion of etherified starch for sudden hearing loss. In both the affected periocular skin and healthy skin there was lysosomal storage of etherified starches with a specific antibody in histiocytes, endothelial cells, basal keratinocytes, and small nerves. In the periocular skin there was more deposition of etherified starches, in addition to distinct xanthomatous changes and features of lymphedema. In addition, there was a 50% reduction in the pH-dependent activity of the lysosomal alpha-glu-cosidase in cultured fibroblasts. 

Skin Increase in dark basal keratinocytes Focal hyperplasiaAiyperkeratosis... 

Although the exact mechanism by which mustard produces tissue injury is not known, the mechanism of action has been suggested to be its ability to directly alkylate DNA. This DNA alkylation and cross-linking in rapidly dividing cells such as basal keratinocytes, mucosal epithelium, and bone marrow precursor cells leads to cellular death and inflammatory reactions. Systemic effects with extensive exposures include bone marrow inhibition, with a drop in the white blood cell count, and gastrointestinal tract damage. 

Thickening of the stratum comeum occurs as an adaptive response to prolonged UVB exposure. The stratum comeum proliferates through increased synthesis of keratin by basal keratinocytes. 

The authors concluded that sulphur mustard injury to human skin commences at the level of the basal keratinocyte and thus confirmed the original theories of McAdams (1956). They also drew some parallels with thermal injury, which is also thought to act by disrupting the basal epidermal layer (Cullumbine, 1947). These ultrastructural observations and the belief that blistering results from dermo-epidermal separation at the level of the epidermal basement membrane have now been confirmed by im-munohistochemical studies (Lindsay and Rice, 1995). 

The cells of origin of thymopoietin appear to be the thymic epithelial cells. By the use of a heteroantiserum and immunofluorescent techniques, the peptide was shown to localize to thymic epithelial cells (Goldstein, 1977). In more recent studies it has been demonstrated that both the subcapsular cortical as well as the medullary thymic epithelial cells react with antithymopoietin antibodies (Haynes, 1984). A molecule that is indistinguishable from thymopoietin by immunoassay is also present in one major extra-thymic site, the epidermis. Two to fifteen percent of human epidermal cells appear to endogenously produce thymopoietin in tissue culture. These cells have been characterized as basal keratinocytes of the epidermis (Chu et al., 1983). 

Tumor promoters convert some basal keratinocytes to an embryonic phenotype similar to the dark cells thereby supplying a positive environment for the dark cells to expand in number. 

Cytokeratin 15 (CK15) Squamous cell carcinoma, basal cell carcinoma Basal keratinocytes, fetal epidermis... 

Lavker, R.M. and Sun, T.T. (1982). Heterogeneity in epidermal basal keratinocytes morphological and functional correlations. Science, 215 1239-1241. 

Figure 1 Low-power (200X) micrograph of human adult skin showing the dermis (A) and epidermis (B). The nucleated basal keratinocytes define the beginning of the viable epidermis which is composed of five to six cell layers. As the basal keratinocytes migrate to the surface of the skin, they flatten and lose their nucleus until they resemble thin sheets. At this point, the keratinocytes are called comeocytes and this layer is called the stratum comeum (C). In this sample, the stratum comeum is partially detached due to tissue processing. However, note the onionskin-like appearance of the stratum comeum. Beneath the basal keratinocytes is the dermis (A). The dermis is composed of a pale-staining papillary (PD) layer and dense reticular (RD) layer. Note the prominent collagen bundles (arrows) within the reticular layer.

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