Stress-induced mast cell activation in glabrous and hairy skin

Abstract

Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.

Figure 1

Histochemical aspect of mast cells (→) with (a) Giemsa staining; (b) acidified toluidine blue staining; (c) Alcian blue-Safranin O staining. Magnification 400x.

Figure 2

(a) Normal mast cells (→) localized near vasculonervous structures in hairy skin. Alcian blue-Safranin O staining. 400x magnification; (b) Degranulated mast cells (→) in immediate vicinity of vasculonervous structures in glabrous skin. Alcian blue-Safranin O staining. Magnification 400x.

Figure 3

Comparative analysis of the proportion of degranulated mast cells. (a) In glabrous skin, brief exposure to stress induced a significant increase in the proportion of degranulated mast cells and prolonged exposure to stress was associated with a gradual return to normal value of degranulated mast cells. (b) In hairy skin, acute exposure to stress induced an amplification of mast cell degranulation process that was maintained after prolonged exposure to stress. Error bars represent the standard error of the mean (SEM). *P < 0.05, **P < 0.01, ***P < 0.001, two-tailed multiple comparison test.

Figure 4

Electron microscopy image from the rat control group. Two dermal mast cells (M) with uniform electron-dense granules (g), placed near a nerve bundle containing a Schwann cell (S) and unmyelinated nerve fibers (f). Collagen (C) in the surrounding background.

Figure 5

Electron microscopy picture from Stress 1 day rat group. Mast cell with dense granules (g), granules emptied of content (e), granules showing altered electron densities (i), and granules on the verge of releasing the content into the extracellular space (s). Collagen (C) and fibroblast (Fb).

Figure 6

Electron micrograph from Stress 21 days rat group. A dermal mast cell (MC) with dense granules and granules that show altered electron densities (arrows), indicating a process of mast cell activation. Collagen fibers (Col) in the surrounding background.