Acute and chronic hypoxia as well as 7-day recovery from chronic hypoxia affects the distribution of pulmonary mast cells and their MMP-13 expression in rats

Abstract

Chronic hypoxia results in pulmonary hypertension due to vasoconstriction and structural remodelling of peripheral lung blood vessels. We hypothesize that vascular remodelling is initiated in the walls of prealveolar pulmonary arteries by collagenolytic metalloproteinases (MMP) released from activated mast cells. Distribution of mast cells and their expression of interstitial collagenase, MMP-13, in lung conduit, small muscular, and prealveolar arteries was determined quantitatively in rats exposed for 4 and 20 days to hypoxia as well as after 7-day recovery from 20-day hypoxia (10% O2). Mast cells were identified using Toluidine Blue staining, and MMP-13 expression was detected using monoclonal antibody. After 4, but not after 20 days of hypoxia, a significant increase in the number of mast cells and their MMP-13 expression was found within walls of prealveolar arteries. In rats exposed for 20 days, MMP-13 positive mast cells accumulated within the walls of conduit arteries and subpleurally. In recovered rats, MMP-13 positive mast cells gathered at the prealveolar arterial level as well as in the walls of small muscular arteries; these mast cells stayed also in the conduit part of the pulmonary vasculature. These data support the hypothesis that perivascular pulmonary mast cells contribute to the vascular remodelling in hypoxic pulmonary hypertension in rats by releasing interstitial collagenase.

Figure 1

Distribution of pulmonary Toluidine Blue-detected mast cells in control and hypoxic rats. Means (± SEM) of absolute number of mast cells per 50 mm² of the left lung section.

Figure 2

Distribution of pulmonary MMP-13-expressing mast cells in control and hypoxic rats. Means (± SEM) of absolute number of mast cells expressing MMP-13 per 50 mm² of the left lung section.

Figure 3

Newly muscularized double-laminated (small arrows) prealveolar arteriole with MMP-13-positive mast cells (long arrows) in its adventitia. 4-day hypoxic rat. Anti-MMP-13/Fast Red and Haematoxylin. Bar = 50 μm.

Figure 4

A group of MMP-13-positive mast cells (long arrow) in adventitia of a newly muscularized supernumerary arteriole (small arrow) outbranched from a conduit artery (asterisk). 4-day hypoxic rat. Anti-MMP-13/Fast Red and Haematoxylin. Bar = 50 μm.

Figure 5

Small muscular artery with well developed elastic laminae and elastic network within its tunica media (small arrows) and a MMP-13-positive mast cell with released granules (long arrow). 20-day hypoxic rat. Anti-MMP-13/gold conjugate/silver enhanced and Toluidine Blue, semi-thin section. Bar = 20 μm.