Epithelial growth by rat vibrissae follicles in vitro requires mesenchymal contact via native extracellular matrix

An in vitro assay utilizing the rat vibrissa anagen follicle as a model for studying the epithelial-mesenchymal interactions (EMI) in hair growth is described. Through selective disruption of the epithelial-mesenchymal interface, we investigate whether the specialized extracellular matrix (ECM) of the dermal papilla and basement membrane zone (BMZ) serves a crucial function in hair follicle EMI. Epithelial bulbs incubated intact within their follicular sheaths incorporate thymidine primarily into cells of the hair matrix and outer root sheath, as shown by autoradiography. However, after removal of its mesenchymal associations (dermal papilla and extrabulbar connective tissue), the epithelial bulb showed no incorporation. Neither externally added collagen (type I or IV) nor the basement membrane components in Matrigel could substitute for the growth supporting influence of native surrounding stroma. Mechanical separation of the bulb from the dermal papilla in the basement membrane zone inhibited thymidine incorporation by the epithelium even though mesenchyme was still in close proximity. Enzymatic digestion of the dermal papilla ECM and the basal lamina by Dispase, a fibronectinase and type IV collagenase, also inhibited bulb growth without evidence of cytotoxicity. These experiments suggest that direct epithelial to mesenchymal contact is required for the support of follicular epithelial growth in vitro and that specific ECM components, possibly fibronectin and/or type IV collagen, rather than diffusable factors alone, play a crucial role in the mechanism of hair follicle EMI. The in vitro system described here provides an alternative to developmental EMI models and may serve as a valuable tool for studying EMI in the adult mammalian organism.

Telogen skin contains an inhibitor of hair growth

We have investigated whether C57B1-6 mouse skin with all its follicles in the telogen stage of the hair cycle contains a hair-growth inhibitory activity, as opposed to skin with anagen follicles. Crude aqueous extracts of whole telogen mouse skin (TE), anagen skin (AE) or vehicle alone (V) were injected intraperitoneally into mice in which anagen had previously been induced by plucking of telogen hair follicles. Injection of TE, but not AE or V, significantly retarded the development of anagen follicles, as measured by macroscopic and quantitative microscopic hair growth parameters (skin pigmentation and thickness, appearance of trichohyaline granules) and the incorporation of tritiated thymidine into mouse skin from animals previously treated with either TE or V (skin organ culture). This inhibitory activity seemed to be localized to the epidermis and was also present in rat epidermis. We suggest that this apparently non-species-specific inhibitor present in telogen skin may play a role in regulating the hair cycle in rodents.

Are L-tyrosine and L-dopa hormone-like bioregulators?

Some amino acids have bioregulatory functions, which far exceed those of precursors for proteins or of substrates for specific enzymes. Two of these amino acids, L-tyrosine and L-dopa, are precursors to melanin and catecholamines. In vertebrates, they can act as inducers and regulators of the melanogenic apparatus and of MSH receptors--two quite complex functions that could hardly be performed by mere substrates. Focussing on the pigmentary system as a study model, we therefore explore the hypothesis that L-tyrosine and L-dopa act as hormone-like bioregulators in mammals, with melanocytes regulating tyrosine and dopa activity via their metabolic consumption.

Beta-adrenergic receptors in nasal tissue with reference to their role in asthma and atopy

Thirty-three samples of nasal tissue (turbinates and polyps) were collected and assayed for beta-adrenergic receptor (BAR) sites (radio-ligand assay). Patients were divided into groups: 1) nasal turbinates, 2) nasal polyps, both under the aspects of atopy and bronchial hyperreactivity. Different radiobinding was found in both groups: Patients A with high BAR and patients B with low BAR numbers. There was no correlation between BAR numbers--clinical symptoms and bronchial hyperreactivity. Generally the BAR numbers were higher in turbinates (p less than 0.01) than in polyps and in nonatopic compared to atopic patients (p less than 0.005). "Affinity state 1" BAR are equal in all groups; however, "affinity state 2"BAR are significantly less in polyps (p less than 0.05). In 50% of the examined cases there was a combination of polyps, asthma and atopy putting foreward a common line of pathogenesis in this entity. It is discussed that the underlying inflammation (allergic and non-allergic) is the cause for reduced BAR numbers in the effected tissue. So far nasal tissue seems to be like a mirror compared to the results from lower respiratory tract tissue with respect to beta-adrenergic receptors.

The induction of anagen hair growth in telogen mouse skin by cyclosporine A administration

One clinical complication of immunosuppressive cyclosporine A (CsA) therapy is the stimulation of hair growth. Since few pharmacologic agents cause hypertrichosis, CsA appears particularly interesting for investigating the mechanisms which control normal hair formation. Previous investigators have shown that CsA affects the hair growth of the laboratory rat, several genetic variants of mice, as well as humans, and they have concluded that CsA influences keratinization predominantly. Using a well-defined in vivo assay which measures the induction of hair follicle growth, we report here that CsA induces resting (telogen) follicles to enter active growth (anagen) in normal laboratory mice (C57 B1-6), i.e., animals with a normal hair cycle. The experiments indicate that the rate of anagen induction is dependent on the dose, time course, and method of administration and that it may be mediated via a direct action of CsA on the skin and its appendages. These studies suggest that understanding the molecular mechanisms of CsA action on hair growth will help elucidate the mechanisms of normal anagen induction.

The psoriatic epidermal lesion and anagen hair growth may share the same "switch-on" mechanism

Based on striking parallels between the cell kinetics in the epidermal lesion of psoriasis and the proliferation of hair matrix keratinocytes during the anagen phase of the hair growth cycle, the hypothesis is proposed that both phenomena may share the same "switch-on" mechanism. Particular emphasis is placed on a comparison between the Koebner phenomenon in psoriasis and wounding-induced anagen hair growth. In discussing alternative theoretical models for the proposed common "switch-on" mechanism, some useful experimental tools are suggested. Research into the mechanisms which control epithelial proliferation in psoriasis and hair growth may provide new insights into other growth processes, such as embryonic organogenesis and neoplasia, in which similar epithelial-mesenchymal interactions play a pivotal role.