Uncontrolled fibrosis due to excessive accumulation of extracellular matrix proteins in the lacrimal glands of patients with chronic graft-versus-host disease (cGVHD) is well documented. Heat-shock protein 47 (HSP47) is involved in the molecular maturation of collagen and has been shown to have a fibrogenic role in various fibrotic diseases. In this study, the role of HSP47 in the pathogenesis of lacrimal gland of patients with cGVHD was investigated.
The expression of HSP47, Ki67 (a proliferation marker), types I and III collagen, and alpha-smooth muscle actin (alpha-SMA) was examined in tissue sections and in primary cultures of fibroblasts obtained from the lacrimal glands of patients with cGVHD (n = 8) and Sjögren's syndrome (SS; n = 7).
Tissue sections of the lacrimal glands of patients with cGVHD showed markedly increased expression of HSP47 in fibroblasts around the medium-sized ducts than did those from patients with SS. The elevated expression of HSP47 in patients with cGVHD was mostly detected in Ki67-positive fibroblasts and was associated with increased accumulation of types I and III collagen in and around the fibrotic areas. Primary fibroblast cultures generated from cGVHD lacrimal gland showed higher HSP47 mRNA expression than did fibroblasts isolated from SS biopsy tissue, as determined by RT-PCR (P < 0.05). In contrast, alpha-SMA was higher in the SS than cGVHD fibroblasts at both mRNA and protein levels, and more lacrimal gland fibroblasts in the SS were positive for alpha-SMA than cGVHD (P < 0.01).
In cGVHD, increased expression of HSP47 may promote excessive collagen assembly in and around the periductal areas where fibroblasts are mostly in an active state. The less alpha-SMA in the cGVHD lacrimal gland fibroblasts suggests a relative lack of myofibroblastic transformation. It is likely that fibroblasts incapable of myofibroblastic transformation are the main source of HSP47 and collagen production, and the resultant effect is the periductal fibrotic changes seen in lacrimal glands of patients with cGVHD.