Akt2, but not Akt1 or Akt3 mediates pressure‐stimulated serum‐opsonized latex bead phagocytosis through activating mTOR and p70 S6 kinase

Abstract

Monocytes and macrophages play critical roles in innate host defense and are sensitive to mechanical stimuli. Tissue pressure is often altered in association with inflammation or infection. Low pressure (20 mmHg), equivalent to normal tissue pressure, increases phagocytosis by primary monocytes and PMA-differentiated THP-1 macrophages, in part by FAK and ERK inhibition and p38 activation. PI-3K is required for macrophage phagocytosis, but whether PI-3K mediates pressure-stimulated phagocytosis is not known. Furthermore, little is known about the role played by the PI-3K downstream Kinases, Akt, and p70 S6 kinase (p70S6K) in modulating macrophage phagocytosis. Thus, we studied the contribution of PI-3K, Akt, and p70S6K to pressure-increased serum-opsonized bead phagocytosis. Pressure-induced p85 PI-3K translocation from cytosolic to membrane fractions and increased Akt activation by 36.1 +/- 12.0% in THP-1 macrophages. LY294002 or Akt inhibitor IV abrogated pressure-stimulated but not basal phagocytosis. Basal Akt activation was inhibited 90% by LY294002 and 70% by Akt inhibitor IV. Each inhibitor prevented Akt activation by pressure. SiRNA targeted to Akt1, Akt2, or Akt3 reduced Akt1, Akt2, and Akt3 expression by 50%, 45%, and 40%, respectively. However, only Akt2SiRNA abrogated the pressure-stimulated phagocytosis without affecting basal. Pressure also activated mTOR and p70S6K. mTORSiRNA and p70S6K inhibition by rapamycin or p70S6KSiRNA blocked pressure-induced, but not basal, phagocytosis. Changes in tissue pressure during inflammation may regulate macrophage phagocytosis by activation of PI-3K, which activates Akt2, mTOR, and p70S6K.

Propofol inhibits pressure-stimulated macrophage phagocytosis via the GABAA receptor and dysregulation of p130cas phosphorylation

“…Exposure to pressure increased phagocytosis in monocytes from healthy volunteers (22.9 Ϯ 3.3 vs. 31.8 Ϯ 4.7%, n ϭ 8, P Ͻ 0.005; Fig. 1A), consistent with our previous observations (51,52). However, pressure failed to increase phagocytosis in monocytes isolated from surgical patients receiving anesthesia (Fig.…”

“…We previously reported that increased extracellular pressure (20 mmHg above ambient pressure) stimulates serum-opsonized latex bead uptake by primary isolated monocytes from healthy volunteers as well as PMA-differentiated human monocytic THP-1 cells (THP-1 macrophages) (51)(52)(53). Several reports suggest that anesthetic agents and surgical stress may affect phagocytic cell function (5,23,28) and that tissue pressure may be increased within surgical wounds or at surgical sites postoperatively (56).…”

“…Next, we examined whether propofol modulates macrophage phagocytosis in vitro in primary isolated peripheral monocytes obtained from healthy volunteers and in THP-1 macrophages. Initially, to define the optimal condition for in vitro propofol treatment, we tested the exposure time to propofol and the propofol dose using THP-1 macrophages, in which we previously demonstrated a response to pressure similar to that of primary monocytes (51,52). THP-1 macrophages were pretreated for 15 min-4 h with 10 g/ml propofol or the equivalent amount of Intralipid, the vehicle in which propofol is delivered clinically ( Fig.…”

“…We previously reported that exposure to constant low extracellular pressure (20 mmHg) enhances phagocytosis by human peripheral monocytes and PMA-differentiated THP-1 macrophages through activation of p38 and the phosphatidylinositol 3-kinase (PI3K)-Akt-p70S6k pathway and by inhibition of focal adhesion kinase (FAK) and ERK (51)(52)(53). This is important because interstitial tissue pressure may increase at wound sites after surgery.…”

Akt/PKB isoforms expression in the human lumbar herniated disc: correlation with clinical and MRI findings

“…The (PI3K)-Akt pathway mediates inflammatory responses, while the activation of Akt/PKB has been implicated in macrophage phagocytosis of foreign bodies [22,23]. Our hypothesis is reinforced by the findings of Shiratsuchi and Basson who report that changes in tissue pressure during inflammation may regulate macrophage phagocytosis by the activation of PI-3K/Akt2/PKBb, but not Akt1/PKBa and Akt3/PKBc [24].…”