124 Chapter 4 higher levels of transmigration in macrophages cultured on fibrous collagen that we found before [11], as they also express higher levels of PEDF. Interestingly, in lung tissue of patients with IPF, more PEDF expression was found than in lung tissue of controls [22]. PEDF is suggested to have a protective effect in the pathogenesis of fibrosis [23] and therefore the higher levels found in fibrosis suggest a compensatory mechanism trying to control fibrosis development. Indeed, two studies have shown that increased expression of PEDF in macrophages attenuated collagen synthesis by fibroblasts in a macrophage-mediated manner [24,25]. This ties in with recent findings of downregulation of PEDF in acute exacerbations of IPF compared to stable disease as these exacerbations predispose to rapid progression of fibrosis [26]. In addition to PEDF, the proteins dynactin subunit 4, RNA-binding protein 42, 28S ribosomal protein S15, and copper-transporting ATPase 1 were also expressed significantly more by macrophages on fibrous collagen than on globular collagen. No relevant data were found connecting dynactin subunit 4, RNA-binding protein 42, or 28S ribosomal protein S15 with macrophage function or lung fibrosis. However, the copper-transporting ATPase 1 (ATP7A) protein is of particular interest, since it has been suggested to play an important role in macrophage wound healing responses. In fact, ATP7A-downregulation inhibited macrophage infiltration in a mouse model for dermal wounding [27]. The higher levels of ATP7A may therefore also be linked to our previous results showing more migration in macrophages cultured on fibrous collagen [11]. Furthermore, ATP7A was shown to be required for copper delivery to members of the lysyl oxidase (LOX) family [28]. These copper-dependent enzymes play an important role in collagen cross-linking and higher activity of these enzymes has been described in patients with IPF [3,29,30]. Higher expression of ATP7A may therefore contribute to remodeling of non-organized fibrous collagen by activating members of the LOX family. Only four proteins were expressed more than two-fold higher by macrophages cultured on globular collagen than on fibrous collagen. Thioredoxin reductase-1 (Txnrd1) is an important component of the thioredoxin system, in which it reduces and thereby activates thioredoxin by transferring electrons from NADPH. This thioredoxin system has both anti-oxidative as well as anti-inflammatory properties and has been associated with antifibrotic effects in bleomycin-induced pulmonary fibrosis [31,32]. Cotreatment of macrophages with IL4 and recombinant thioredoxin promoted the development of an anti-inflammatory phenotype characterized by higher expression of CD206 [33]. It is therefore conceivable that the higher levels of CD206 we previously found in macrophages cultured on globular collagen [11] are related to the higher levels of Txnrd1. In addition to Txnrd1, three other proteins
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