Macrophage uptake of ¹²⁵I-LDL is non-saturable.

<p>A. LDLR−/− macrophages were incubated with 1 mg/ml of LDL for 0–24 h and cholesterol accumulation was then assessed. B. LDLR−/− macrophages were incubated 24 h with increasing concentrations of ¹²⁵I-LDL, and then ¹²⁵I-LDL uptake was assessed. Uptake values represent the sum of cell-associated and degraded ¹²⁵I-LDL. The range of cell-associated and degraded ¹²⁵I-LDL was 7–13% and 87–93%, respectively.</p

The effect of possible inhibitors of fluid-phase pinocytosis on LDL uptake and net cholesterol accumulation in wild-type M-CSF-differentiated macrophages.

<p>Wild-type bone marrow-derived macrophages were pretreated 1 h with drug vehicle or the indicated drug. For cholesterol accumulation, macrophages then were incubated with 1 mg/ml LDL and inhibitor for 6 h. For ¹²⁵I-LDL uptake, macrophages then were incubated with 200 µg/ml ¹²⁵I-LDL and inhibitor for 6 h. All incubations were performed in serum-free medium containing 50 ng/ml M-CSF. The percent inhibition of net cholesterol accumulation compares macrophages treated with LDL alone and LDL with inhibitor (except the experiment that compares macrophages treated with LDL and dynamin peptide inhibitor with LDL and control peptide) after basal cholesterol values were subtracted from each. The percent inhibition of ¹²⁵I-LDL uptake compares macrophages treated with ¹²⁵I-LDL alone and ¹²⁵I-LDL with inhibitor. Control values for macrophages incubated with LDL alone or ¹²⁵I-LDL alone are indicated in parentheses. For cholesterol accumulation, control values are expressed as nmol net cholesterol accumulation/mg cell protein. For ¹²⁵I-LDL uptake, control values are expressed as µg ¹²⁵I-LDL uptake/mg cell protein. The range of cell-associated and degraded ¹²⁵I-LDL for all treatments except bafilomycin A1-treated macrophages was 15–19% and 82–86%, respectively. Cell-associated and degraded ¹²⁵I-LDL for bafilomycin A1-treated macrophages was 91% and 9%, respectively. * = <i>p</i><0.05. ** = <i>p</i><0.01. *** = <i>p</i><0.001. ND = not determined. “+” indicates a decrease in the number of macropinosomes and “−” indicates no effect on macropinosomes. “−” in percent inhibition columns indicates stimulation rather than inhibition.</p

Macropinosome formation is M-CSF dependent.

<p>A and B. Wild-type macrophages were differentiated with M-CSF for 7 days and visualized by phase-contrast microscopy following the treatments described below. Macrophages differentiated with M-CSF were pretreated 30 min with DMSO drug vehicle (A), or 5 µM of cFMS (i.e., M-CSF receptor) tyrosine kinase inhibitor, GW2580 (B). Pretreatment was carried out without either serum or M-CSF. Withdrawal of M-CSF caused disappearance of the macrophage vacuoles. Subsequently, these macrophage cultures were treated 30 min with fresh serum-free medium containing M-CSF (50 ng/ml) without (A) or with GW2580 (B). Macrophages treated with M-CSF without GW2580 showed numerous vacuoles shown to be macropinosomes in Video S1. In contrast, there was complete inhibition of macropinosome formation when macrophage cultures were treated with GW2580 (also see Video S2). Scale bar in B = 75 µm and also applies to A. (C) Wild-type macrophages were incubated 24 h with 1 mg/ml LDL without or with 5 µM GW2580, and then cholesterol accumulation was assessed. Macrophages incubated without LDL had 111±3 nmol cholesterol/mg protein. ** = <i>p</i><0.01.</p

LDL-derived cholesterol accumulation occurs independently of class I PI3K isoforms.

<p>Cholesterol accumulation after 24 h-incubation without or with 1 mg/ml LDL was assessed in M-CSF differentiated macrophages cultured from wild-type, PI3Kγ-KI, PI3Kβ-KI, and PI3Kδ-KI mice.</p

The effect of PI3K inhibitors and cytochalasin D on LDL uptake and net cholesterol accumulation in LDLR −/− macrophages.

<p>LDLR−/− bone marrow-derived macrophages were pretreated 1 h with either drug vehicle, 50 µM LY294002, 100 nm wortmannin, or 4 µg/ml cytochalasin D. For cholesterol accumulation, macrophages then were incubated with 1 mg/ml LDL and inhibitor for 24 h. For ¹²⁵I-LDL uptake, macrophages then were incubated 5 h with 200 µg/ml ¹²⁵I-LDL and inhibitor. All incubations were performed in serum-free medium containing 50 ng/ml M-CSF. The percent inhibition of net cholesterol accumulation compares macrophages treated with LDL alone and LDL with inhibitor after basal cholesterol values were subtracted from each. The percent inhibition of ¹²⁵I-LDL uptake compares macrophages treated with ¹²⁵I-LDL alone and ¹²⁵I-LDL with inhibitor. ** = <i>p</i><0.01. *** = <i>p</i><0.001. All inhibitors showed almost complete inhibition of macropinosome formation as assessed by phase-microscopy. For LY294002 and wortmannin experiments, control macrophages incubated with LDL or ¹²⁵I-LDL alone showed net cholesterol accumulation and ¹²⁵I-LDL uptake values of 226±8 nmole/mg cell protein and 2.7±0.1 µg/mg cell protein, respectively. For cytochalasin D experiments, control macrophages incubated with LDL or ¹²⁵I-LDL alone showed net cholesterol accumulation and ¹²⁵I-LDL uptake values of 230±2 nmole/mg cell protein and 3.4±0.1 µg/mg cell protein, respectively. The range of cell-associated and degraded ¹²⁵I-LDL for all treatments was 19–33% and 67–81%, respectively.</p

The effect of PI3K inhibitors and cytochalasin D on net cholesterol accumulation in wild-type macrophages.

<p>Wild-type bone marrow-derived macrophages were pretreated 1 h with either drug vehicle, 50 µM LY294002, 100 nm wortmannin, or 4 µg/ml cytochalasin D. Macrophages then were incubated with 1 mg/ml LDL and inhibitor for 6 h. Incubations were performed in serum-free medium containing 50 ng/ml M-CSF. The percent inhibition of net cholesterol accumulation compares macrophages treated with LDL alone and LDL with inhibitor after basal cholesterol values were subtracted from each. ** = <i>p</i><0.01. *** = <i>p</i><0.001. All inhibitors almost completely inhibited macropinosome formation as assessed by phase-microscopy. For the LY294002 experiment, control macrophages incubated with LDL alone showed net cholesterol accumulation of 31±2 nmole/mg cell protein. For the wortmannin and cytochalasin D experiments, control macrophages incubated with LDL alone showed net cholesterol accumulation of 78±2 nmole/mg cell protein.</p

Fluid-phase pinocytosis mediates LDL uptake.

<p>(A) Wild-type macrophages were incubated 6 h with either 25 µg/ml ¹²⁵I-LDL alone, or 25 µg/ml ¹²⁵I-LDL and 500 µg/ml unlabeled LDL. CD36 KO macrophages (ΔCD36) and SRA KO macrophages (ΔSRA) macrophages were incubated 6 h with 25 µg/ml ¹²⁵I-LDL alone. (B) Wild-type macrophages were incubated 6 h with either 25 µg/ml ¹²⁵I-AcLDL alone, or 25 µg/ml ¹²⁵I-AcLDL and 500 µg/ml unlabeled AcLDL. CD36 KO macrophages (ΔCD36) and SRA KO macrophages (ΔSRA) macrophages were incubated 6 h with 25 µg/ml ¹²⁵I-AcLDL alone. Incubations were performed in serum-free medium containing 50 ng/ml M-CSF. Uptake values represent the sum of cell-associated and degraded ¹²⁵I-labeled lipoprotein. The range of cell-associated and degraded ¹²⁵I-LDL was 17–21% and 79–83%, respectively. The range of cell-associated and degraded ¹²⁵I-AcLDL was 16–18% and 82–84%, respectively. ¹²⁵I-LDL uptake was not competed with excess unlabeled LDL consistent with fluid-phase pinocytosis mediating uptake. Statistical tests compare each treatment group with wild-type macrophages incubated with 25 µg/ml ¹²⁵I-AcLDL. * = <i>p</i><0.05. ** = <i>p</i><0.01. *** = <i>p</i><0.001. There was no statistical difference between macrophage groups incubated with ¹²⁵I-LDL.</p

Wild-type and LDL−/− macrophages incubated with LDL accumulate similar levels of cholesterol.

<p>Wild-type and LDLR−/− macrophages were incubated with 1 mg/ml LDL for 24 h and then total cholesterol accumulation was assessed. The baseline cholesterol levels for wild-type and LDLR−/− macrophages were 107±10 nmol cholesterol/mg protein and 122±9 nmol cholesterol/mg protein, respectively.</p

Age-related impairment of adaptive immune response to CHIKV.

<p>(A) Popliteal LNs collected and quantified from either naïve or CHIKV-infected A and O mice at day 3, 7, or 9 post-infection. The LN draining from the CHIKV-inoculated foot is indicated as dLN and from the non-inoculated foot as ndLN. Table under graph indicates the average fold-increase from naïve for each age in either the dLN or ndLN (<i>n</i> = 6–8 per group). Horizontal lines indicate the median. Statistical significance determined by student’s <i>t</i>-test. (B-C) Lymphocytes from popliteal LNs on d7 post-infection were stimulated with CHIKV peptides in the presence of protein transport inhibitor. Total number of IFNγ⁺ CD4 T cells (B) and frequency (C) for each age. Data are mean ± SEM (<i>n</i> = 10 per group). Statistical significance determined by unpaired Student’s <i>t</i>-test. (D) CHIKV-specific IgM and (E) IgG2c in serum determined by ELISA at the indicated day post-infection. Data are mean (<i>n</i> = 4–24 per group). Statistical significance was determined by two-way ANOVA with Bonferroni post-test. (F) Plaque reduction neutralizing test on serum from days 9 and 60 post-infection. Data are mean + SEM (<i>n</i> = 12 per group). Statistical significance was determined by two-way ANOVA with Bonferroni post-test. (G) Serum samples collected from patients experiencing acute CHIKV-disease were evaluated by plaque reduction neutralizing test. Data are mean + SEM (<i>n</i> = 24 young and 15 aged). Statistical significance was evaluated by unpaired student’s <i>t</i>-test. In all panels black indicates A, red indicates O; * <i>P</i>< 0.05; ** <i>P</i>< 0.01; *** <i>P</i>< 0.001.</p

Blocking TGFβ prevents acute CHIKV-induced disease in O mice.

<p>A and O B6 mice were inoculated and treated with 100ug of anti-TGFβ antibody or isotype control and swelling was measured daily as described in Methods. Data are mean ± SEM (n = 8 per group). Statistical significance was determined using mixed model, repeated measures analyses of variance (ANOVA) as detailed in Statistics. Red stars indicate reduction of swelling in O mice from αIgG1 to αTGFβ treated; black stars indicate reduction of swelling in A mice from αIgG1 to αTGFβ treated.</p