Local proliferation dominates lesional macrophage accumulation in atherosclerosis

During the inflammatory response that drives atherogenesis, macrophages accumulate progressively in the expanding arterial wall1,2. The observation that circulating monocytes give rise to lesional macrophages3–9 has reinforced the concept that monocyte infiltration dictates macrophage build-up. Recent work indicates, however, that macrophages do not depend on monocytes in some inflammatory contexts10. We therefore revisited the mechanism of macrophage accumulation in atherosclerosis. We show that murine atherosclerotic lesions experience a surprisingly rapid, 4-week, cell turnover. Replenishment of macrophages in these experimental atheromata depends predominantly on local macrophage proliferation rather than monocyte influx. The microenvironment orchestrates macrophage proliferation via the involvement of scavenger receptor (SR)-A. Our study reveals macrophage proliferation as a key event in atherosclerosis and identifies macrophage self-renewal as a therapeutic target for cardiovascular disease

Non-adenine based purines accelerate wound healing

Wound healing is a complex sequence of cellular and molecular processes that involves multiple cell types and biochemical mediators. Several growth factors have been identified that regulate tissue repair, including the neurotrophin nerve growth factor (NGF). As non-adenine based purines (NABPs) are known to promote cell proliferation and the release of growth factors, we investigated whether NABPs had an effect on wound healing. Full-thickness, excisional wound healing in healthy BALB/c mice was significantly accelerated by daily topical application of NABPs such as guanosine (50% closure by days 2.5′.8). Co-treatment of wounds with guanosine plus anti-NGF reversed the guanosine-promoted acceleration of wound healing, indicating that this effect of guanosine is mediated, at least in part, by NGF. Selective inhibitors of the NGF-inducible serine/threonine protein kinase (protein kinase N), such as 6-methylmercaptopurine riboside abolished the acceleration of wound healing caused by guanosine, confirming that activation of this enzyme is required for this effect of guanosine. Treatment of genetically diabetic BKS.Cg-m+/+lepr db mice, which display impaired wound healing, with guanosine led to accelerated healing of skin wounds (25% closure by days 2.8′.0). These results provide further confirmation that the NABP-mediated acceleration of cutaneous wound healing is mediated via an NGF-dependent mechanism. Thus, NABPs may offer an alternative and viable approach for the treatment of wounds in a clinical setting

Self-renewing resident arterial macrophages arise from embryonic CX3CR1+ precursors and circulating monocytes immediately after birth

Resident macrophages densely populate the normal arterial wall, yet their origins and the mechanisms that sustain them are poorly understood. Here we use gene-expression profiling to show that arterial macrophages constitute a distinct population among macrophages. Using multiple fate-mapping approaches, we show that arterial macrophages arise embryonically from CX3CR1+ precursors and postnatally from bone marrow–derived monocytes that colonize the tissue immediately after birth. In adulthood, proliferation (rather than monocyte recruitment) sustains arterial macrophages in the steady state and after severe depletion following sepsis. After infection, arterial macrophages return rapidly to functional homeostasis. Finally, survival of resident arterial macrophages depends on a CX3CR1-CX3CL1 axis within the vascular niche

Effect of dexamethasone in smoke-exposed influenza-infected mice.

<p>Female C57BL/6 mice were exposed to room air (open bars) or cigarette smoke (closed bars). One hour prior to treatment with vehicle or inoculation with influenza A virus, mice were gavaged with 3mg/kg of dexamethasone (dex). Mice were gavaged daily with 3 mg/kg of dex. (A) BAL samples were obtained at 5 days post-infection and total cells were enumerated. Mononuclear cell and neutrophil differentials were also assessed. Clinical presentation in animals at the time of sacrifice (B), and viral titres (C) were also determined. Clinical presentation (D), and viral titres (E) were also assessed in mice sacrificed at day 7 post-infection. Data are presented as the means ± SEMs for n = 4–6 animals per group.</p

Effect of a PPAR-γ agonist, pioglitazone, on antiviral responses in smoke-exposed mice.

<p>C57BL/6 mice were exposed to room air (open bars) or cigarette smoke (closed bars). Starting on the second day of smoke exposure, mice were gavaged daily with 60 mg/kg of pioglitazone (Pio). Following four days of smoke-exposure, mice were given a sterile vehicle or inoculated with influenza A virus intranasally. (A) Broncho-alveolar lavage (BAL) samples were obtained at 5 days post-infection and total cells were enumerated. Mononuclear cell and neutrophil differentials were also assessed. (B) Body weight was monitored throughout the course of the viral infection and expressed relative to body weight on the day 0 of infection. (C) Viral titres were also determined. Percentages of TNFα/iNOS producing dendritic cells (D), and activated CD4+ and CD8+ T cells (E) were obtained from the live gate of CD45+ cells. Data are presented as the means ± SEMs for n = 5–6 animals per group.</p

Influenza infection of smoke-exposed animals.

<p>C57BL/6 mice were exposed to room air (open bars) or cigarette smoke (closed bars). Subsequently, mice were given a PBS vehicle or inoculated with influenza A virus intranasally. (A) Broncho-alveolar lavage (BAL) samples were obtained and total cells were enumerated at the indicated times post-infection. Mononuclear cell and neutrophil differentials were also assessed. (B) Light photomicrographs of representative hematoxylin and eosin –stained cross sections of lung tissue were taken at 5 days post-infection. Data are presented as means ± SEMs for n = 3–12 animals per group.</p

Viral titres and type I interferon responses.

<p>C57BL/6 mice were exposed to room air (open bars) or cigarette smoke (closed bars). Mice were infected with influenza A virus. (A) Viral titres were determined in lung homogenates at the indicated times post-infection. (B) The presence of type I interferons at day 3 post-infection was also determined by plating the indicated dilutions of BAL on confluent monolayers of IRF-3 deficient mouse embryonic fibroblasts and performing a vesicular-stomatitis virus (VSV) plaque reduction assay. 100% relative intensity indicates the absence of type I interferon activity, whereas 0% relative intensity indicates sufficient levels of type I interferon to completely prevent VSV-GFP replication. Data are presented as the means ± SEMs for n = 3–17 animals (A), and n = 5 animals (B) per group.</p