Osteopontin a bioactive milk protein with immunological properties

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1 Osteopontin a bioactive milk protein with immunological properties Esben S. Sørensen Section for Molecular Nutrition Department of Molecular Biology and Genetics Aarhus University, Denmark

2 Proteins in human and bovine milk Component Human milk g/l Bovine milk Casein Whey proteins α-lactalbumin β-lactoglobulin lactoferrin secretory IgA 1.15 lysozyme serum albumin From: Fox (1992) Minor milk proteins under investigation at our laboratory MUC1 MUC15 Lactadherin Adipophilin Osteopontin NPC2 PP3/Lactophorin and many others

3 Osteopontin First isolated from bone matrix tissue Key molecule in calcification processes Upregulated expression at bone fractures, infections, inflammations, wound healing and many others Activator of the cell-mediated immune response Functions as a cytokine binds several integrin receptors Very high concentrations in milk!

4 Osteopontin many isoforms (Sørensen et al., 1995; Christensen et al., 2005, 2008, 2010, 2012)

5 OPN modification determines integrin specificity MMP, thrombin, cathepsin D and plasmin

6 Osteopontin in milk The concentration in bovine milk is approximately 18 mg/l In human breast milk the osteopontin concentration is significantly higher Modification and cleavage patterns are similar in human and bovine milk What is the function of osteopontin in milk? Inhibitor of calcium precipitation/crystallization? Part of the innate immune system? - activates the cellular immune response - binds bacteria and induces phagocytosis of these

7 Osteopontin in human breast milk High degree of variation in osteopontin content: mg/l Average: 138 mg/l ~ 2.1% of total protein Milk/Infant Formula OPN conc. (mg/l) Bovine milk 18 Human milk 138 Infant formulae (Schack et al., 2009, J. Dairy Sci.)

8 Osteopontin in infant plasma Plasma samples 263 ng/ml 342 ng/ml 35 ng/ml (Schack et al., 2009, J. Dairy Sci.) The high content of osteopontin in milk and in the umbilical cord and plasma from 3-month old children could suggest a function in neonate development.

9 Osteopontin and cell-mediated immune response Breastfeeding protects from diseases like diarrhea, respiratory infections and infections of the gastrointestinal tract After birth the infant is exposed to a large number of microorganisms and a colonization of the gut occurs Osteopontin stimulation of human intestinal immune cells

10 Osteopontin as an opsonin? Immune cell expression of osteopontin increases after infection Osteopontin influences immune cell cytokine signalling Osteopontin attracts immune cells to site of infection Upon infection osteopontin KO mice have a reduced ability to clear the infection OPN binding to bacteria OPN binding to monocytes OPN induced monocyte chemotaxis OPN induced phagocytosis of bacteria

11 Binding of osteopontin to bacteria (Schack et al., 2009, J. Immunol.) Osteopontin binds to bacteria in a dose dependent manner - and at physiological relevant concentration ([OPN-human milk] ~140 ug/ml). The binding is calcium dependent

12 Binding of osteopontin to MNCs Osteopontin is secreted by most immune cells including Dc, Mø, T- and NK cells Does osteopontin bind to blood lymphocytes or monocytes? Resting T cells NK cells B cells The binding is specific for osteopontin

13 Osteopontin induces monocyte migration The observation that osteopontin interacts directly with monocytes suggests that osteopontin may influence on monocyte function

14 Can osteopontin mediate phagocytosis of bacteria? Osteopontin can bind to monocytes and to bacteria and can induce migration of immune cells. bacteria-cypher5e PMA activated u937 cells Incubation with OPN or control CypHer5E is flourescent at acidic ph

15 Osteopontin mediates phagocytosis of bacteria Schack et al. J. Immunol. (2009) Bacterial opsonization with osteopontin enhances phagocytosis (+17%)

16 Phagocytosis of osteopontin coated beads Latex beads u937 OPN BSA? IgG1 Incubation??

17 Osteopontin enhances phagocytosis of beads

18 Osteopontin in innate immunity a model Osteopontin 138 mg/ml in human milk activates the cellular immune system binds to bacteria binds to monocytes promotes monocyte migration induces phagocytosis of bacteria Osteopontin could be an important immunological factor in milk

19 Osteopontin in infant formula The effect of OPN added to infant formula has been tested on the intestinal transcriptome in infant rhesus monkeys (Donovan et al., 2011). Addition of OPN to infant formula to 125 mg/l reduced the difference in differentially expressed genes between formula-fed and breastfed infants by 0.5 fold. Clinical trial Effect of Infant Formula With Bovine Milk Osteopontin on Infant Growth, Health and Immune functions-a Double-blind Randomized Trial (Biostime Inc. and Arla Foods; PI s Lönnerdal & Peng)

20 Orally administered milk osteopontin rescues mice from alcohol-induced liver injury Mice were fed either the control or the ethanol Lieber-DeCarli diet for 3 weeks, following which mice were given ethanol in combination with 200 μg/ml BSA or with milk OPN for 10 days. H&E staining shows micro- (yellow arrows) and macrovesicular (green arrows) steatosis by ethanol feeding plus BSA, which is partially prevented by treatment with milk OPN (A). The scores for inflammation, hepatocyte ballooning degeneration, and steatosis (B). Serum ALT activity (C) and LPS levels (D). n = 6; P < 0.05 and P < 0.01 for m-opn versus BSA. Ge et al., 2013, Am J Physiol Gastrointest Liver Physiol Ge et al., 2014, Hepatology

21 Suppression of tumour growth by orally administered milk osteopontin Effect of milk OPN on growth of cells cells were injected subcutaneously at cells per mouse. OPN was added to the drinking water at the indicated concentration starting 5 days later, and tumour size was measured every other day with calipers. Tumour growth rate in mice fed different doses of OPN. (Rittling et al., 2014, Br. J. Cancer)

22 Acknowledgements Aarhus University MBG Brian Christensen Lotte Schack Lise Møller Fogh Eva Kläning Torben E. Petersen Mount Sinai Medical Scool, NY Natialia Nieto Aarhus University Health and Hospital Per Höllsberg Uffe B. Skov Sørensen Thomas Vorup-Jensen Jens Kelsen Jørgen Agnholt Aksel Lange san Funding Danish Dairy Research Foundation The Danish Council for Independent Research The Milk Protein Research Consortium Arla Foods Ingredients The Novo Nordisk Foundation The Carlsberg Foundation The Forsyth Institute, MA Susan R. Rittling Rutgers University, NJ David T. Denhardt Susan