Osteopontin (OPN) is a proinflammatory marker produced by systemic immune and central nervous system (CNS) resident cells. We examined, if the level of OPN in the cerebrospinal fluid (CSF) and blood ...is associated with late-time regional brain volumes and white matter (WM) lesion load in MS. Concentrations of OPN in blood and CSF were related to MRI findings 10.1 ± 2.0 years later in 46 patients with MS. OPN concentration was measured by ELISA, while regional brain volumes and lesion load was assessed by magnetic resonance imaging (MRI) using 3D MPRAGE sequence and automated MR volumetry. OPN measured in the CSF was associated with several regional brain volumes and WM lesion load measured 10.1 ± 2.0 years later. CSF OPN concentration correlated with long-term enlargement of lateral- and inferior lateral ventricles and the elevation of gross CSF volume, in conjunction with the reduction of several cortical/subcortical gray matter and WM volumes. Serum OPN showed no long-term association with regional brain volumes. OPN measured from the CSF but not from the serum was associated with lower regional brain volumes measured a decade later, indicating the primary role of inflammation within the CNS in developing long-term brain related alterations.
Abstract
Osteopontin (OPN) is a multifunctional protein, initially identified in osteosarcoma cells with its role of mediating osteoblast adhesion. Later studies revealed that OPN is associated with ...many inflammatory conditions caused by infections, allergic responses, autoimmunity and tissue damage. Many cell types in the peripheral immune system express OPN with various functions, which could be beneficial or detrimental. Also, more recent studies demonstrated that OPN is highly expressed in the central nervous system (CNS), particularly in microglia during CNS diseases and development. However, understanding of mechanisms underlying OPN’s functions in the CNS is still limited. In this review, we focus on peripheral myeloid cells and CNS-resident cells to discuss the expression and functions of OPN.
OPN in innate immune cells and CNS-resident cells
Graphical Abstract
Graphical Abstract
Osteopontin (OPN) is a multifunctional protein highly expressed in milk, where it is hypothesized to be involved in immunological signaling via the conserved Arg-Gly-Asp (RGD) integrin-binding ...sequence. Intervention studies have indicated beneficial effects of orally administered OPN in animal and human infants, but the mechanisms underlying these effects are not well described. To induce physiological effects, OPN must resist gastrointestinal transit in a bioactive form. In this study, we subjected bovine milk OPN to in vitro gastrointestinal transit, and characterized the generated fragments using monoclonal antibody and mass spectrometric analyses. We found that the fragment Trp27-Phe151 containing the integrin-binding RGD sequence resisted in vitro gastric digestion. This resistance was dependent on glycosylation of threonine residues near the integrin-binding sequence in both human and bovine milk OPN. Furthermore, the fragment Trp27-Phe151 retained the ability to interact with integrins in an RGD-dependent process. These results suggest a mechanism for how ingested milk OPN can induce physiological effects via integrin signaling in the intestine.
Breast milk contains a high concentration of osteopontin (OPN), a protein having multiple functions. In contrast, infant formula is low in OPN. A randomized clinical trial was performed to evaluate ...effects of adding a highly enriched bovine OPN fraction to formula, and infants whose mothers had already decided not to breast-feed were recruited. They were fed regular formula (F0) or the same formula with bovine OPN at 65 (F65) or 130 (F130) mg/L (50% and 100% of human milk level, respectively) from 1 to 6 months of age and were compared with a reference group of breast-fed (BF) infants.
Morbidity was recorded daily and 3-day dietary records collected monthly. Anthropometry was assessed monthly, and blood samples were taken at 1, 4, and 6 months of age. Hematology and iron status, serum cytokines, plasma amino acids, and blood urea nitrogen were analyzed.
Formulas were well tolerated and there were no significant differences in formula intake or growth among the formula-fed groups. The F130 group had significantly lower plasma threonine than the F0 and F65 groups, and significantly lower plasma branched-chain amino acids (BCAAs) than the F0 group and, thus, was closer to BF infants. Plasma TNF-α was higher in formula-fed infants than in BF infants. Among the formula-fed groups, the proinflammatory cytokine TNF-α was significantly lower in the F65 and F130 groups than in the F0 group, suggesting that OPN downregulates inflammatory cytokines and thus affects immune function.
Addition of OPN to infant formula changes amino acid metabolism and cytokine responses of FF infants and makes them more similar to BF infants. The lower prevalence of pyrexia in the F130 infants than in F0 infants suggests that adding OPN may confer health benefits.
Osteopontin (OPN) is a multifunctional cytokine that is strongly expressed in healing wounds and fibrotic lesions, both of which are characterized by the formation of myofibroblasts. We examined the ...role of OPN in myofibroblast differentiation induced by the profibrotic cytokine transforming growth factor-beta1. In cultured cardiac or dermal fibroblasts treated with transforming growth factor-beta1, there was a 2- to 5-fold increase in the expression of the myofibroblast markers alpha-smooth muscle actin and extradomain A fibronectin but no significant increase of these proteins in OPN-null fibroblasts. Phalloidin staining for actin filaments and immunostaining for alpha-smooth muscle actin and focal adhesion proteins showed reduced stress fibers, focal adhesions, and lamellipodia in OPN-null fibroblasts compared with wild-type cells. OPN-null fibroblasts exhibited 40% to 60% less spreading, 50% less resistance to detachment by shear force, and a approximately 3-fold reduction in collagen gel contraction. These defects were partially rescued by ectopic expression of OPN. Mass spectrometric analysis of proteins in focal adhesions formed on collagen type I beads revealed an enrichment of HMGB1 protein in wild-type cells, whereas HMGB1 was not detected in OPN-null cells. Treatment of wild-type cells with small interfering RNA to knock down OPN reduced transforming growth factor-beta1-induced alpha-smooth muscle actin and HMGB1 to levels observed in OPN-null cells. These studies demonstrate that OPN is required for the differentiation and activity of myofibroblasts formed in response to the profibrotic cytokine transforming growth factor-beta1.
Illustration of BBR-induced osteogenic differentiation of MSCs. In MSCs, BBR promotes activation of the canonical Wnt pathway resulting in translocation o f β-catenin into the nucleus to form a ...complex with TCF1 on the Runx2 promoter for its induction, subsequently upregulate Runx2 target genes expression, such as OPN and OCN, and consequently stimulates osteogenesis. Effects of BBR on osteogenesis are potently repressed by specific Wnt signaling specific inhibitor DKK-1 or β-catenin siRNA.
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•BBR alone can enhance the osteogenic differentiation of MSCs in a dose-dependent model.•A sequential combination of BBR and DKK-1 or β-catenin specific siRNA transfection administration inhibits the expression of osteogenic transcriptional factors such as OPN and OCN, and Wnt/β-catenin signaling core factor β-catenin.•BBR administration triggers osteogenic differentiation of MSCs in vitro though canonical Wnt/β-catenin signaling.
Berberine (BBR) has recently been reported to be extensively used for musculoskeletal disorders such as osteoporosis through enhancing osteogenic differentiation, inhibiting osteoclastogenesis and bone resorption and repressing adipogenesis. Although canonical Wnt signaling plays a crucial role in suppressing bone marrow-derived mesenchymal stem cells (MSCs) commitment to the chondrogenic and adipogenic lineage and enhancing osteogenic differentiation, no previous reports have shown an association between BBR-induced osteogenesis and Wnt/β-catenin signaling pathway. In this study, we aimed to investigate the stimulatory effect and the mechanism of BBR on osteogenic differentiation of human bone marrow-derived MSCs. MSCs were isolated from bone marrow specimens and treated with different concentration of BBR. Cell viability was measured by the WST-8 assay. Effects of BBR on osteogenic differentiation of MSCs were assessed by von Kossa staining, ALP staining and ALP activity. Osteogenic specific genes, chondrogenic and adipogenic related marker genes were determined by quantitative real-time polymerase chain reaction analysis. Western blot and Immunofluorescence staining were performed to analyze OCN and OPN, and β-catenin expression in the presence or absence of BBR combined with DKK-1 or β-catenin siRNA transfection. Increasing concentration of BBR (3, 10 and 30μM) promoted osteogenic differentiation and osteogenic genes expression after incubation for various days compared with DMSO group, whereas expression levels of chondrogenic and adipogenic related marker genes were dramatically suppressed. After treated with 10μM BBR for 7 days, β-catenin, OPN and OCN expression were significantly induced, which could be effectively suppressed by the addition of DKK-1 or β-catenin siRNA β-catenin. Interestingly, the expression level of Runx2 gene was also decreased by inhibiting the transduction of Wnt/β-catenin signaling. These findings suggest that BBR can stimulate osteogenic differentiation of MSCs not only by enhancing Runx2 expression but also by activating canonical Wnt/β-catenin signaling pathway, and canonical Wnt/β-catenin signaling pathway is in part responsible for BBR-induced osteogenic differentiation of MSCs in vitro. BBR is a potential pharmaceutical medicine by enhancing osteogenic differentiation for bone disorders, such as osteoporosis.
A matricellular protein, osteopontin (OPN), is expressed in response to mechanical stress and similar stimuli in the heart, integrates the inter-ECM signal transduction network of component cells, ...and maintains efficient contractility through quantitative and qualitative control of extracellular matrix (ECM) proteins. In particular, OPN is re-expressed in the process of tissue damage; combines with other cell growth factors, cytokines, chemokines, and proteases as a cytokine itself or as an adhesion molecule; and controls the differentiation and growth of cells involved in re-storation of tissues by controlling inter-cellular signal transduction and production of ECM proteins through regulation of expression levels and activity. A study using mice lacking a functional OPN gene indicated that tissue restoration fails and collagen deposition is inhibited through matrix metalloproteinases (MMPs) in mice lacking OPN. Thus, while OPN accelerates the cardiovascular remodeling process, it also regulates the balance of various inter-cellular activities. In addition, OPN not only promotes arteriosclerosis but is also closely associated with angiogenesis. With the roles of OPN expected to be clinically elucidated, the clinical use of OPN for control of cardiovascular remodeling may be feasible. Points (1) Osteopontin (OPN) efficiently propagates contraction in the heart as a matricellular protein and thereby controls ECM proteins both quantitatively and qualitatively. (2) The quantitative and qualitative control of ECM proteins is involved in interaction with OPN receptors including those of the integrin family, CD44, and others. (3) OPN promotes myocardial remodeling through TGFβ and MMPs. (4) OPN not only promotes arteriosclerosis but is also closely associated with arteriosteogenesis. (5) In animals lacking OPN, tissue remodeling process is inhibited, especially in terms of fibrosis after myocardial infarction. (6) While the significance of OPN as an immune system molecule is still unclear in detail, the significance of OPN in the regenerative immune system has begun to be determined.
The regulatory events guiding progenitor activation and differentiation in adult white adipose tissue are largely unknown. We report that induction of brown adipogenesis by β3-adrenergic receptor ...(ADRB3) activation involves the death of white adipocytes and their removal by M2-polarized macrophages. Recruited macrophages express high levels of osteopontin (OPN), which attracts a subpopulation of PDGFRα+ progenitors expressing CD44, a receptor for OPN. Preadipocyte proliferation is highly targeted to sites of adipocyte clearance and occurs almost exclusively in the PDGFRα+ CD44+ subpopulation. Knockout of OPN prevents formation of crown-like structures by ADRB3 activation and the recruitment, proliferation, and differentiation of preadipocytes. The recruitment and differentiation of PDGFRα+ progenitors are also observed following physical injury, during matrix-induced neogenesis, and in response to high-fat feeding. Each of these conditions recruits macrophages having a unique polarization signature, which may explain the timing of progenitor activation and the fate of these cells in vivo.
•β3 adrenergic induction of brown adipogenesis in WAT involves white adipocyte death•M2 macrophages release osteopontin, which recruits PDGFRα+ progenitors•PDGFRα+ progenitors proliferate and differentiate at sites of adipocyte clearance•Macrophage recruitment of progenitors is a general feature of adult adipogenesis
A major hurdle for functional recovery after both spinal cord injury and cortical stroke is the limited regrowth of the axons in the corticospinal tract (CST) that originate in the motor cortex and ...innervate the spinal cord. Despite recent advances in engaging the intrinsic mechanisms that control CST regrowth, it remains to be tested whether such methods can promote functional recovery in translatable settings. Here we show that post-lesional AAV-assisted co-expression of two soluble proteins, namely insulin-like growth factor 1 (IGF1) and osteopontin (OPN), in cortical neurons leads to robust CST regrowth and the recovery of CST-dependent behavioral performance after both T10 lateral spinal hemisection and a unilateral cortical stroke. In these mice, a compound able to increase axon conduction, 4-aminopyridine-3-methanol, promotes further improvement in CST-dependent behavioral tasks. Thus, our results demonstrate a potentially translatable strategy for restoring cortical dependent function after injury in the adult.
•Osteopontin (OPN) sensitizes the responses of adult corticospinal neurons to IGF1•OPN/IGF1 promotes CST regrowth and relevant functional recovery after spinal cord injury•CST sprouting induced by OPN/IGF1 mediates functional recovery after stroke•4-AP-MeOH further improves behavioral performance after OPN/IGF1 treatment
Liu et al. showed that post-lesional AAV-OPN/IGF1 treatment leads to robust regrowth of corticospinal axons and relevant behavioral recovery in both spinal cord injury and cortical stroke models, demonstrating a potentially translatable strategy for restoring cortical function in the adult.
Osteopontin (OPN) is involved in different liver pathologies in which metabolic dysregulation is a hallmark. Here, we investigated whether OPN could alter liver, and more specifically hepatocyte, ...lipid metabolism and the mechanism involved. In mice, lack of OPN enhanced cholesterol 7α-hydroxylase (CYP7A1) levels and promoted loss of phosphatidylcholine (PC) content in liver; in vivo treatment with recombinant (r)OPN caused opposite effects. rOPN directly decreased CYP7A1 levels through activation of focal adhesion kinase-AKT signaling in hepatocytes. PC content was also decreased in OPN-deficient (OPN-KO) hepatocytes in which de novo FA and PC synthesis was lower, whereas cholesterol (CHOL) synthesis was higher, than in WT hepatocytes. In vivo inhibition of cholesterogenesis normalized liver PC content in OPN-KO mice, demonstrating that OPN regulates the cross-talk between liver CHOL and PC metabolism. Matched liver and serum samples showed a positive correlation between serum OPN levels and liver PC and CHOL concentration in nonobese patients with nonalcoholic fatty liver. In conclusion, OPN regulates CYP7A1 levels and the metabolic fate of liver acetyl-CoA as a result of CHOL and PC metabolism interplay. The results suggest that CYP7A1 is a main axis and that serum OPN could disrupt liver PC and CHOL metabolism, contributing to nonalcoholic fatty liver disease progression in nonobese patients.
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