Pressure modulates monocyte migration

Mechano-Immunomodulation: Mechanoresponsive Changes in Macrophage Activity and Polarization

In recent years, biomaterial- and scaffold-based immunomodulation strategies were implemented in tissue regeneration efforts for manipulating macrophage polarization (a.k.a. phenotype or lineage commitment, or differentiation). Yet, most of our understanding of macrophage phenotype commitment and phagocytic capacity is limited to how physical cues (extracellular matrix stiffness, roughness, and topography) and soluble chemical cues (cytokines and chemokines released from the scaffold) influence macrophage polarization. In the context of immune response-tissue interaction, the mechanical cues experienced by the residing cells within the tissue also play a critical role in macrophage polarization and inflammatory response. However, there is no compiled study discussing the effect of the dynamic mechanical environment around the tissues on macrophage polarization and the innate immune response. The aim of this comprehensive review paper is 2-fold; (a) to highlight the importance of mechanical cues on macrophage lineage commitment and function and (b) to summarize the important studies dedicated to understand how macrophage polarization changes with different mechanical loading modalities. For the first time, this review paper compiles and compartmentalizes the studies investigating the role of dynamic mechanical loading with various modalities, amplitude, and frequency on macrophage differentiation. A deeper understanding of macrophage phenotype in mechanically dominant tissues (i.e. musculoskeletal tissues, lung tissues, and cardiovascular tissues) provides mechanistic insights into the design of mechano-immunomodulatory tissue scaffold for tissue regeneration.

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

Surgical stress and anesthesia result in systemic immunosuppression. Propofol, a commonly used anesthetic agent, alters immune cell functions. Previously, we demonstrated that extracellular pressure increases macrophage phagocytosis. We hypothesized that propofol might influence pressure-induced macrophage phagocytosis in monocytes from patients undergoing surgery. Pressure (20 mmHg above ambient pressure) augmented phagocytosis in monocytes from non-propofol-anesthetized patients but reduced phagocytosis in monocytes from propofol-anesthetized patients. In vitro, propofol stimulated phagocytosis but reversed pressure-induced phagocytosis in THP-1 macrophages and monocytes from healthy volunteers. The GABA(A) receptor antagonists picrotoxin and SR-95531 did not affect basal THP-1 phagocytosis or prevent pressure-stimulated phagocytosis. However, picrotoxin and SR-95531 negated the inhibitory effect of pressure in propofol-treated cells without altering propofol-induced phagocytosis. Phosphorylation of the adaptor protein p130cas was inversely related to phagocytosis: it was inhibited by pressure or propofol but increased by pressure + propofol compared with propofol alone. Reduction of p130cas by small interfering RNA in THP-1 macrophages increased basal phagocytosis and prevented pressure and propofol effects. In conclusion, propofol may alter macrophage responses to pressure via the GABA(A) receptor and p130cas, whereas pressure also acts via p130cas but independently of GABA(A) receptors. p130cas may be an important target for modulation of macrophage function in anesthetized patients.

Amlodipine reduces the antimigratory effect of diclofenac in spontaneously hypertensive rats

Amlodipine, an antihypertensive drug, and diclofenac, an antiinflammatory drug, may generally be combined, particularly in elderly patients; therefore, the potential for their interaction is high. We aim to determine if amlodipine interferes with the antimigratory effect of diclofenac. For this, male spontaneously hypertensive rats (SHRs) were treated with either diclofenac (1 mg.kg.d, 15 d) alone or combined with amlodipine (10 mg.kg.d, 15 d). Leukocyte rolling, adherence, and migration were studied by intravital microscopy. Diclofenac did not change (180.0 +/- 2.3), whereas amlodipine combined (163.4 +/- 5.1) or not (156.3 +/- 4.3) with diclofenac reduced the blood pressure (BP) levels in SHR (183.1 +/- 4.4). Diclofenac and amlodipine reduced leukocyte adherence, migration, and ICAM-1 expression, whereas only diclofenac reduced rolling leukocytes as well. Combined with amlodipine, the effect of the diclofenac was reduced. Neither treatment tested increased the venular shear rate or modified the venular diameters, number of circulating leukocytes, P-selectin, PECAM-1, L-selectin, or CD-18 expressions. No difference could be found in plasma concentrations of both drugs given alone or in association. In conclusion, amlodipine reduces leukocyte migration in SHR, reducing endothelial cell ICAM-1 expression. Amlodipine reduces the effect of the diclofenac, possibly by the same mechanism. A pharmacokinetic interaction as well as an effect on the other adhesion molecules tested could be discarded.

The role of hydrostatic pressure in foam cell formation upon exposure of macrophages to LDL and oxidized LDL

Hypertension is a major, established risk factor for atherosclerosis. How it interacts to exacerbate the cellular processes involved in atherogenesis is unclear. This initial, preliminary study examined how hydrostatic pressure influenced the formation of foam cells from human macrophages exposed to low-density lipoprotein (LDL) or oxidized LDL (OxLDL). The results demonstrated that both LDL and OxLDL, at physiological concentration, were taken up by cultured human macrophages and foam cells were formed. This led to cell detachment and death within 24h. These effects were more rapid and more pronounced in pressurized cultures. We conclude that exposure of cell cultures to cyclical hydrostatic pressure (CHP) aggravated the adverse effects of the lipids on the macrophages.

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

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.

Alteration of Leukocyte–Endothelial Cell Interaction During Aging in Retinal Microcirculation of Hypertensive Rats

PURPOSE

Hypertension, one of the more common chronic diseases affecting the elderly, has been reported to influence leukocyte-endothelial cell interaction. The leukocyte-mediated inflammatory process contributes to age-related changes in vessels. This study was designed to evaluate age-related changes in leukocyte-endothelial cell interaction in the hypertensive rat retina.

METHODS

Male spontaneous hypertensive rats (SHR; 1.5, 3, 6, 12, and 20 months of age) and age-matched Wistar-Kyoto rats (WKY) were used. The number of accumulated leukocytes was counted in sections of flat-mounted retinal tissue. The expression of intercellular adhesion molecule-1 (ICAM-1) and CD18 (the common beta-chain of ICAM-1 ligands) was evaluated. Retinal thickness was evaluated histologically.

RESULTS

The number of accumulated leukocytes and the expression of ICAM-1 and CD18 increased in the aged retina. The number of leukocytes that accumulated and the expression of CD 18 were significantly higher in the SHR group than in the WKY group (P < 0.01). In addition, retinal thickness decreased with age.

CONCLUSION

Leukocyte-endothelial cell interaction increased in the aged retina and these changes were more severe in SHR retina than in WKY retina. This increased interaction was first observed at 3 months, a relatively young age.

Differential regulation of monocyte/macrophage cytokine production by pressure

BACKGROUND

Cytokine production by macrophages is essential for the inflammatory response. Normal human interstitial tissue pressure is 20 to 30 mm Hg, but generally decreases in acute inflammation.

METHODS

We compared the effect of 20 mm Hg increased pressure (approximating normal interstitial tissue pressure) with that of ambient pressure (resembling pressure in inflamed tissues) on tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta production by undifferentiated (monocytic) and PMA (phorbol 12-, myristate 13-acetate)-differentiated (macrophage-like) THP-1 cells with or without lipopolysaccharide (LPS) (10 ng/mL).

RESULTS

Pressure stimulated spontaneous macrophage TNF-alpha secretion (30.5 +/- 6.3 vs. 49.1 +/- 2.8 pg/mL, P <.02), but not monocyte TNF-alpha secretion. Pressure did not stimulate IL-1beta release. As expected, LPS increased basal cytokine release. After LPS stimulation, pressure still tended to stimulate macrophage TNF-alpha, but inhibited monocyte TNF-alpha secretion (P <.05). In contrast, pressure inhibited IL-1beta release by both LPS-treated monocytes (986 +/- 134 vs. 595 +/- 226 pg/mL, P <.02) and macrophages (3,112 +/- 229 vs. 979 +/- 61 pg/mL, P <.01).

CONCLUSIONS

Extracellular pressure may regulate TNF-alpha and IL-1beta secretion differentially by monocytes and macrophages.

Blood Pressure-Independent ETA and AT1 Receptor Blocker Effects on the Coronaries of Rats Harboring Human Renin and Angiotensinogen Genes

BACKGROUND

Blood pressure-independent (BP) effects of angiotensin (Ang) II and endothelin (ET) on coronaries (remodeling) in high renin hypertension are incompletely understood.

METHODS

We studied the effects of subdepressor doses of Ang II receptor (AT1) blockade with losartan (10 mg/kg/day gavage) and endothelin A receptor (ETA) blockade with LU135252 (30 mg/kg/day) on the coronaries of rats harboring human renin and angiotensinogen genes (dTGR). Nontransgenic Sprague-Dawley rats were controls. The rats were treated between the ages of 6 and 10 weeks. Coronary cross-sectional area [CSA; 0.79 x (external diameter2 - internal diameter2)], cell proliferation, and infiltration of monocytes/macrophages were determined.

RESULTS

Monotherapy did not lower BP while combination treatment did (p < 0.05). All treatments reduced mortality (p < 0.01). CSA was decreased by all treatments compared to vehicle, independent of blood pressure (p < 0.05). Extensive proliferation by PCNA staining and infiltration of ED-1-positive cells was diminished by both treatment and the combination.

CONCLUSIONS

The data show that Ang II promotes coronary inflammation and remodeling, in part independent of blood pressure but dependent upon ET signaling. Combination treatment directed at both pathways may improve outcome, independent of blood pressure reduction.

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Extracellular pressure stimulates macrophage phagocytosis by inhibiting a pathway involving FAK and ERK

We hypothesized that changes in extracellular pressure during inflammation or infection regulate macrophage phagocytosis through modulating the focal adhesion kinase (FAK)-ERK pathway. Undifferentiated (monocyte-like) or PMA-differentiated (macrophage-like) THP-1 cells were incubated at 37 degrees C with serum-opsonized latex beads under ambient or 20-mmHg increased pressure. Pressure did not affect monocyte phagocytosis but significantly increased macrophage phagocytosis (29.9 +/- 1.8 vs. 42.0 +/- 1.6%, n = 9, P < 0.001). THP-1 macrophages constitutively expressed activated FAK, ERK, and Src. Exposure of macrophages to pressure decreased ERK and FAK-Y397 phosphorylation (77.6 +/- 7.9%, n = 7, P < 0.05) but did not alter FAK-Y576 or Src phosphorylation. FAK small interfering RNA (SiRNA) reduced FAK expression by >75% and the basal amount of phosphorylated FAK by 25% and significantly increased basal macrophage phagocytosis (P < 0.05). Pressure inhibited FAK-Y397 phosphorylation in mock-transfected or scrambled SiRNA-transfected macrophages, but phosphorylated FAK was not significantly reduced further by pressure in cells transfected with FAK SiRNA. Pressure increased phagocytosis in all three groups. However, FAK-SiRNA-transfected cells exhibited only 40% of the pressure effect on phagocytosis observed in scrambled SiRNA-transfected cells so that phagocytosis inversely paralleled FAK activation. PD-98059 (50 microM), an ERK activation inhibitor, increased basal phagocytosis (26.9 +/- 1.8 vs. 31.7 +/- 1.1%, n = 15, P < 0.05), but pressure did not further increase phagocytosis in PD-98059-treated cells. Pressure also inhibited ERK activation after mock transfection or transfection with scrambled SiRNA, but transfection of FAK SiRNA abolished ERK inhibition by pressure. Pressure did not increase phagocytosis in MonoMac-1 cells that do not express FAK. Increased extracellular pressure during infection or inflammation enhances macrophage phagocytosis by inhibiting FAK and, consequently, decreasing ERK activation.

Effects of efonidipine on platelet and monocyte activation markers in hypertensive patients with and without type 2 diabetes mellitus

We compared the levels of microparticles, platelet activation markers, soluble cell adhesion molecules, and soluble selectins between hypertensive patients with and without type 2 diabetes and control subjects. Binding of anti-glycoprotein IIb/IIIa and anti-glycoprotein Ib monoclonal antibodies to platelets did not differ significantly between the hypertensive patients and controls, but platelet expression of activation markers (CD62P, CD63, PAC-1, and annexin V) was higher in the hypertensive patients. Platelet-derived microparticle (PDMP) and monocyte-derived microparticle (MDMP) levels were significantly higher in the hypertensive patients than in the controls. Soluble ICAM-1, VCAM-1, P-selectin, and E-selectin levels were also higher in the hypertensive patients, and they were significantly higher in the hypertensive patients with diabetes. After treatment with efonidipine, the levels of PDMPs, CD62P-, CD63-, PAC-1-, and annexin V-positive platelets, sICAM-1, sVCAM-1, sP-selectin, and sE-selectin all decreased significantly. The MDMP levels decreased, and the decrease was significant in the hypertensive patients with diabetes. These findings suggest that administration of efonidipine to hypertension patients with diabetes may prevent the development of cardiovascular complications caused by cell adhesion molecules or activated platelets and monocytes.

A novel three-dimensional tissue equivalent model to study the combined effects of cyclic mechanical strain and wear particles on the osteolytic potential of primary human macrophages in vitro

The effects of cyclic mechanical strain and challenge with physiologically relevant doses of submicrometre-size polyethylene (PE) particles on the osteolytic potential of primary human mononuclear phagocytes were investigated. Cells were seeded into a three-dimensional tissue matrix and co-cultured with particles (mean size 0.21 microm) at particle volume to cell number ratios of 7.5, 15, 30 and 100 microm3/cell. Matrices were then either cultured statically or subjected to 20 per cent cyclic compressional strain in the 'ComCell' for 16 h prior to the assessment of cell viability and quantification of the pro-inflammatory cytokine tumour necrosis factor alpha (TNFalpha). The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazdium bromide) assay was shown to be too insensitive to detect changes in cell viability. However, when quantified by the adenosine triphosphate (ATP) assay, cell viability was demonstrated to be reduced following exposure to cyclic strain. Macrophages cultured in the static three-dimensional tissue equivalent model produced very high levels of TNFalpha in response to submicrometre PE particles at a ratio of 100 microm3/cell. Cyclic strain in the absence of particles gave only a small increase in TNFa production. However, the combined effects of strain and particle stimulation at a ratio of 30 microm3/cell resulted in the secretion of significantly more TNFalpha than was produced by macrophages subjected to strain alone, or the cells-only control. This synergy between cyclic strain and PE particle stimulation was only evident when the volume of particles was reduced below the volume that maximally stimulated cells. These results suggest that while cyclic strain may not be the primary factor responsible for macrophage activation and periprosthetic osteolysis, at low particle load, it may contribute significantly to the osteolytic potential of macrophages in vitro or in vivo.

Effects of increased ambient pressure on colon cancer cell adhesion

Forces such as strain modulate intestinal epithelial biology. Shear and pressure influence other cells. The effects of pressure on human colon cancer cells are poorly understood. Increasing ambient pressure for 30 min by 15 mm Hg over atmospheric stimulated adhesion to matrix proteins of four human colon cancer cell lines and primary cells from three human colon cancers, but not bovine aortic smooth-muscle cells. This effect was energy dependent and cation dependent (blocked by azide and chelation), accompanied by tyrosine phosphorylation of intracellular proteins including focal adhesion kinase, and blocked by tyrosine kinase inhibition (genistein, tyrphostin, and erbstatin) and a functional antibody to the beta1 integrin subunit. Although pressure stimulated adhesion even in a balanced salt solution, baseline and pressure-stimulated adhesion were each substantially diminished in the absence of serum. These data suggest that relatively low levels of increased pressure may stimulate malignant colonocyte adhesion by a cation-dependent beta1-integrin-mediated mechanism, perhaps via focal adhesion kinase-related tyrosine phosphorylation. In addition to elucidating another aspect of physical force regulation of colonocyte biology, these findings may be relevant to the effects of increased pressure engendered by colonic peristalsis, surgical manipulation, or laparoscopic surgery on colon cancer cell adhesion.

Angiotensin II AT1-receptor blockade inhibits monocyte activation and adherence in transgenic (mRen2)27 rats

This study investigated whether angiotensin II AT1-receptor blockade with losartan inhibits endothelium-monocyte interactions originating from long-term activation of the renin-angiotensin system in hypertensive transgenic rats [TGR(mRen2)27]. The number of circulating activated monocytes, monocytes adhered to thoracic aorta endothelium, and the extent of endothelial cell injury were compared in adult male transgenic (mRen2)27 and age-matched Hannover Sprague-Dawley (SD) rats after 12 days of continuous subcutaneous administration of saline (120 microl/24 h), losartan (10 mg/kg/24 h), or the vasodilator hydralazine (3 mg/kg/24 h). At the doses administered in this experiment, both losartan and hydralazine normalized mRen2 rat blood pressures equal to values in similarly treated SD rats. Compared with saline infusion, administration of either antihypertensive in mRen2 rats reduced (p<0.05) endothelial cell injury, but only losartan significantly (p<0.05) decreased the number of activated circulating and endothelium-adherent monocytes. Infusion of antihypertensives in SD rats had no effect on blood pressures, monocyte activity, or endothelial injury compared with saline administration. These findings suggest that the recruitment and infiltration of leukocytes into the subendothelium associated with renin-angiotensin system-induced hypertension is partly mediated by pressure-independent AT1-receptor pathways.