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Osteopontin depletion in macrophages perturbs proteostasis via regulation of UCHL1-UPS pathway and activation of mitochondria-mediated apoptosis

ABSTRACT: Osteopontin depletion in macrophages perturbs proteostasis via regulation of UCHL1-UPS pathway and activation of mitochondria-mediated apoptosis Osteopontin (OPN; also known as SPP1), an immunomodulatory cytokine highly expressed in bone marrow derived macrophages (BMM), is known to regulate diverse cellular and molecular immune responses. We previously revealed that glatiramer acetate (GA) stimulation of BMM upregulates OPN expression, promoting an anti inflammatory, phagocytic, pro-healing phenotype, whereas OPN inhibition triggered a pro-inflammatory phenotype. Here, we applied a global proteome profiling via mass spectrometry analysis to gain a mechanistic understanding of OPN suppression versus induction in macrophages. We identified over 630 differentially expressed proteins (DEPs) in OPN knockout (OPNKO) or GA stimulated versus wild type (WT) macrophages. Two topmost downregulated DEPs in OPN deficient macrophages were ubiquitin C terminal hydrolase L1 (UCHL1), a crucial component of ubiquitin proteasome system (UPS), and the anti inflammatory Heme oxygenase 1 (HMOX 1), whereas GA stimulation upregulated their expression. We further confirmed UCHL1 expression in BMM, and its direct interaction with OPN in protein complex. Functional pathway analyses revealed two inversely regulated pathways in OPN-deficient macrophages: activated oxidative stress and lysosome mitochondria-mediated apoptosis (e.g. ROS, Lamp1/2, ATP-synthase subunits, cathepsins, and cytochrome C and B subunits) and inhibited translation and proteolytic pathways (e.g. 60S and 40S ribosomal subunits and UPS proteins). In agreement with the proteome bioinformatics data, Western blot and immunocytochemical analyses revealed that OPN deficiency perturbs protein homeostasis in macrophages, inducing apoptosis and inhibiting translation, whereas GA stimulated OPN induction restores cellular proteostasis. Taken together, OPN is essential for macrophage homeostatic balance via regulation of cell viability, UCHL1 UPS pathway, and protein synthesis, indicating its potential application in immune-based therapy.

INSTRUMENT(S): TripleTOF 5600

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Jennifer Van Eyk

PROVIDER: MSV000091221 | MassIVE | Wed Feb 08 03:32:00 GMT 2023

SECONDARY ACCESSION(S): PXD039950

REPOSITORIES: MassIVE

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Project description:Macrophages and dendritic cells (DCs) differently contribute to the generation of coordinated immune system responses against infectious agents. They interact with microbes through germline-encoded pattern-recognition receptors (PRRs), which recognize molecular patterns expressed by various microorganisms. Upon antigen binding, PRRs instruct DCs for the appropriate priming of natural killer cells, followed by specific T-cell responses. Once completed the effector phase, DCs reach the terminal differentiation stage and eventually die by apoptosis. By contrast, following antigen recognition, macrophages initiate first the inflammatory process and then switch to an anti-inflammatory phenotype for the restoration of tissue homeostasis. Following lipopolysaccharide (LPS)-stimulation the initiation of the apoptotic pathway in DCs is due the activation of NFAT proteins. DC stimulation with lipopolysaccharide (LPS) induces Src-family kinase and phospholipase C (PLC)Î³2 activation, influx of extracellular Ca2+ and calcineurin-dependent nuclear NFAT translocation. The initiation of this pathway is independent of TLR4 engagement, and dependent exclusively on CD14. We asked whether macrophage survival after LPS encounter was due to their inability to activate the Ca2+ pathway. As matter of fact, bone marrow-derived macrophages were unable to mobilize Ca2+ and to translocate NFAT to the. To further investigate whether the Ca2+-NFAT pathway played any role in LPS-stimulated macrophages, we performed a comparative kinetic microarray analysis in conditions allowing or inhibiting NFAT activation. We show here that no modulation of gene expression can be attributed to NFAT. Gene expression analyses were performed using Affymetrix GeneChips in the following groups of murine macrophaghes: 1) CD14-deficient macrophages stimulated with LPS; 2) wt macrophages stimulated with LPS in presence of EGTA; 3) wt macrophages stimulated with LPS. The following kinetic time points were examined: 0, 6 and 24 hours following LPS activation. This experimental setting allowed us to select for effects due to Ca2+ fluxes and exclude the effects due to other causes, particularly the block of TRIF recruitment in CD14-deficient cells and the EGTA effects unrelated to Ca2+ chelation.

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Osteopontin depletion in macrophages perturbs proteostasis via regulation of UCHL1-UPS pathway and activation of mitochondria-mediated apoptosis

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