122 Chapter 4 To investigate if there were any changes to proteins involved in oxidative phosphorylation, we specifically investigated the 33 proteins found in our data involved in the electron transport chain in mitochondria. We found only three proteins higher expressed in macrophages cultured on either globular or fibrous collagen compared to plastic (Cytochrome c oxidase subunit 4, mitochondrial, NADH: Ubiquinone Oxidoreductase Subunit B9, Ubiquinol-Cytochrome C Reductase Core Protein 1) and three lower expressed in macrophages grown on globular collagen compared to fibrous (Cytochrome C Oxidase Subunit 7A2, Superoxide Dismutase 2, Ubiquinol-Cytochrome C Reductase Complex III Subunit VII). Graphs of these six proteins can be found in Supplementary Figure 3. The limited number of differentially expressed protein explains why the process of oxidative phosphorylation was not found enriched. DISCUSSION In this study, we gained insight into the effects of collagen type I morphologies on the proteomic signature of fetal liver-derived alveolar macrophages. Biological process and pathway enrichment analysis revealed clear effects of collagen on the expression of proteins involved in macrophage metabolism. Macrophages grown on collagen favor the expression of proteins involved in glycolysis, although this did not lead to increased glycolytic capacity, possibly because of a compensatory decrease in activity of those proteins. In addition to changes related to the general presence of collagen, fibrous and globular collagen also showed to have morphologyspecific effects on the proteomic profile with prominent induction of Serpinf1 and prominent inhibition of Nabp2 on fibrous compared to globular collagen as the most differentially expressed proteins. Pathway enrichment analysis revealed that macrophages cultured on collagen expressed higher levels of proteins involved in glycolysis and this was independent of collagen morphology. The expression of ATP-dependent 6-phosphofructokinase, liver type (Pfkl), a rate-limiting enzyme in glycolysis, was more than two-fold higher in macrophages cultured on collagen type I. In macrophages, glycolysis is generally associated with an activated, pro-inflammatory phenotype [13]. However, we previously described higher expression of the mannose receptor CD206 and lower expression of major histocompatibility complex II (MHCII) on macrophages cultured on collagen type I, suggesting a more anti-inflammatory/pro-repair phenotype in these alveolar macrophages [11]. This discrepancy may be explained by the recent finding that alveolar macrophages do not depend on glycolysis to produce pro-inflammatory mediators [14]. Furthermore, glycolysis has been associated with a profibrotic macrophage phenotype in bleomycin-induced pulmonary fibrosis in
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