Anjali Desai

Aging Is Associated with an Increase in T Cells and Inflammatory Macrophages in Visceral Adipose Tissue

Age-related adiposity has been linked to chronic inflammatory diseases in late life. To date, the studies on adipose tissue leukocytes and aging have not taken into account the heterogeneity of adipose tissue macrophages (ATMs), nor have they examined how age impacts other leukocytes such as T cells in fat. Therefore, we have performed a detailed examination of ATM subtypes in young and old mice using state of the art techniques. Our results demonstrate qualitative changes in ATMs with aging that generate a decrease in resident type 2 (M2) ATMs. The profile of ATMs in old fat shifts toward a proinflammatory environment with increased numbers of CD206−CD11c− (double-negative) ATMs. The mechanism of this aging-induced shift in the phenotypic profile of ATMs was found to be related to a decrease in peroxisome proliferator-activated receptor-γ expression in ATMs and alterations in chemokine/chemokine receptor expression profiles. Furthermore, we have revealed a profound and unexpected expansion of adipose tissue T cells in visceral fat with aging that includes a significant induction of regulatory T cells in fat. Our findings demonstrate a unique inflammatory cell signature in the physiologic context of aging adipose tissue that differs from those induced in setting of diet-induced obesity.

Leukocyte function in the aging immune system.

Aging is associated with a progressive dysregulation of immune responses. Whether these changes are solely responsible for the observed increased mortality and morbidity amongst the elderly is uncertain. Recent advances have highlighted the age‐associated changes that occur beyond T and B lymphocytes. Additionally, multiple human and animal studies have identified a relationship between chronic low‐grade inflammation and geriatric syndromes, such as frailty, suggesting that the phenomenon of “inflamm‐aging” may provide a rationale for the increased vulnerability to chronic inflammatory diseases in older adults. In the present review, we broadly summarize our current understanding of age‐dependent changes in leukocyte function and their contribution to aging‐related disease processes.

Homocysteine Augments Cytokine-Induced Chemokine Expression in Human Vascular Smooth Muscle Cells: Implications for Atherogenesis

Hyperhomocysteinemia is an independent risk factor for atherosclerosis and atherothrombosis. While in vitro studies have revealed a number of homocysteine-mediated alterations in the thromboregulatory properties of endothelial cells, comparatively little is known about homocysteine-modulated smooth muscle cell function. We observed that exposure of human aortic smooth muscle cells to pathophysiologically relevant concentrations of homocysteine results in concentration-dependent increases in cytokine-induced MCP-1 and IL-8 secretion. RNase protection assays revealed that both MCP-1 and IL-8 mRNA concentrations are increased in homocysteine-treated smooth muscle cells when compared to cells activated with cytokines alone. Homocysteine treatment also increased cytosolic-to-nuclear translocation of the p65 and p50 subunits of the Rel/NF-κB family of transcription factors but had no effect on AP-1 activation. Cumulatively, these data suggest that homocysteine may increase monocyte recruitment into developing atherosclerotic lesions by upregulating MCP-1 and IL-8 expression in vascular smooth muscle cells.

Loxosceles Spider Venom Induces the Production of α and β Chemokines: Implications for the Pathogenesis of Dermonecrotic Arachnidism

Bites from the brown recluse spider and other Loxosceles arachnids result in dermonecrotic skin lesions. Neutrophils (PMN) are essential to the development of Loxosceles-induced skin lesions, but paradoxically, in vitro PMN activation is inhibited by direct exposure to Loxosceles venom. Neutrophil activation occurs in response to a myriad of soluble mediators that include members of both the α and β chemokine families. Because arachnid envenomation results in the exposure of several different cell types to venom, we investigated venom-induced expression of α and β chemokines in both endothelial cells (human umbilical vein; HUVEC) and epithelial cells (A549 pneumocytes). Chemokine-specific capture enzyme immunoassays (EIA) were used to measure Loxosceles deserta venom-induced α chemokines: interleukin-8 (IL-8), growth-related oncogene-alpha (GRO-α), and β chemokines: monocyte chemoattractant protein-1 (MCP-1), and regulated on activation, normal T cell expressed and secreted (RANTES) in cell-free conditioned media from HUVEC and A549 cell monolayers. Exposure of HUVECs (8 h) to Loxosceles venom resulted in the production of IL-8 (5.2 ± 1.30 ng/ml), MCP-1 (1.44 ± 0.11 ng/ml) and GRO-α (1.97 ± 0.15 ng/ml) in a dose and time-dependent manner. Exposure of A549 cell monolayers to venom resulted in IL-8 (7.74 ± 0.30 ng/ml), and MCP-1 (2.61 ± 0.31 ng/ml), but neither GRO-α nor RANTES accumulated during an 8-hour incubation period. Chemokines accumulated in a venom dose and time-dependent manner. Neither cell type secreted RANTES in response to Loxosceles venom. These data indicate that Loxosceles spider venom is a potent inducer of α and β chemokines in both endothelial and epithelial cell types. Based on the established roles of IL-8, MCP-1, and GRO-α, in inflammation, these observations have relevance to the pathophysiology of Loxosceles-Induced dermonecrosis.

Nitric Oxide Modulates MCP-1 Expression in Endothelial Cells: Implications for the Pathogenesis of Pulmonary Granulomatous Vasculitis

Monocyte chemoattractant protein-1 (MCP-1) is a pivotal mediator of angiocentric granuloma formation in glucan-induced pulmonary granulomatous vasculitis. Based on the rationale that mononuclear phagocytes retrieved from granulomas are rich sources of nitric oxide (NO) and that the recruitment of mononuclear phagocytes into lesions abates as granuloma formation slows, we tested the hypothesis that MCP-1 gene expression is regulated by a NO-sensitive mechanism. Preexposure of endothelial cell (EC) monolayers to NO donor compounds markedly reduced cytokine-induced MCP-1 expression and cytosolic-to-nuclear translocation of nuclear factor-kappa B (NF-κB), reversed fluctuations in endothelial reduced glutathione (GSH) pools but did not affect cGMP concentrations. The lungs of mice bearing targeted disruptions of the inducible nitric oxide synthase (iNOS) gene exhibited significantly higher concentrations of MCP-1 following glucan infusion than did those of wild-type mice. Cumulatively, these data suggest that NO suppresses MCP-1 expression by blunting the redox changes associated with cytokine-induced EC activation.

Loxosceles deserta Spider Venom Induces NF-κB-Dependent Chemokine Production by Endothelial Cells

BACKGROUND Loxosceles spider evenomation in man frequently results in disfiguring necrotic skin lesions. Recent studies suggest that several proinflammatory mediators participate in lesion development. We have observed that Loxosceles deserta venom induces production of the chemokines interleukin-8, growth-related oncogene alpha, and monocyte chemoattractant protein-I by human umbilical vein endothelial cells. Members of the Rel/Nuclear factor (NF)-kappaB family of transcription factors are important regulators of many genes involved in immune and inflammatory responses. We hypothesized that Loxosceles-venom-induced chemokine expression in human umbilical vein endothelial cells is mediated by NF-kappaB. METHODS Human umbilical vein endothelial cell monolayers were exposed to activating concentrations of Loxosceles deserta venom. Nuclear extracts of these monolayers were analyzed by electrophoretic mobility shift assay. A direct cause and effect linkage between NF-kappaB activation and chemokine expression by Loxosceles venom was established through examination of the effect of SN50 on interleukin-8 and monocyte chemoattractant protein-1 production using a whole-cell enzyme immunoassay. SN50 is a cell-permeable peptide that specifically blocks cytosolic to nuclear translocation of NF-kappaB. Furthermore, the venom-induced synthesis of chemokine mRNAs was investigated by RNase protection assays. RESULTS Loxosceles deserta venom induces the activation of NF-kappaB in human umbilical vein endothelial cells. Antibodies to p50 and p65, but not to p52, c-Rel, or Rel B, induce supershifts of the DNA-protein complexes formed by oligonucleotide probes and nuclear extracts from venom-activated human umbilical vein endothelial cells. SN50 peptide inhibits NF-kappaB translocation and interleukin-8 and monocyte chemoattractant protein-1 production in activated human umbilical vein endothelial cells. CONCLUSIONS Loxosceles deserta venom induces synthesis of interleukin8 and monocyte chemoattractant protein-1 mRNAs in human umbilical vein endothelial cells. The expression of chemokines occurs via an NF-kappaB-dependent pathway.

Loxosceles deserta Spider Venom Induces the Expression of Vascular Endothelial Growth Factor (VEGF) in Keratinocytes

Evenomation by arachnids of the genus Loxosceles frequently results in disfiguring necrotic skin lesions. The cellular and molecular mechanisms which contribute to lesion development are incompletely defined but appear to involve participation of several pro-inflammatory mediators. We have recently observed that Loxosceles deserta venom induces the production of chemokines in human umbilical vein endothelial cells (HUVECs) and human pulmonary epithelial cells. In the present study we observed that Loxosceles deserta venom induces the expression of vascular endothelial growth factor (VEGF) in human keratinocytes but little in smooth muscle cells and none in pulmonary epithelial cells. A potent endothelial cell-specific mitogen, VEGF induces angiogenesis and vascular permeability in vivo. RNase protection assay data indicate that VEGF mRNA concentrations in keratinocytes are significantly increased at 2 h following venom exposure. These data suggest that keratinocyte-derived VEGF may contribute to the vasodilation, edema and erythema which occur following Loxosceles evenomation.

Nitric oxide suppresses EPO-induced monocyte chemoattractant protein-1 in endothelial cells: implications for atherogenesis in chronic renal disease.

Patients with advanced chronic renal disease (CRD) suffer from excessive morbidity and mortality due to complications of accelerated atherosclerosis. Approximately 90% of dialysis-dependent end stage renal disease patients suffer from anemia. Recombinant human erythropoietin (EPO) in combination with iron has become widely used to treat anemic CRD patients. While treatment with EPO results in improved quality of life it may also contribute to the development of atherosclerosis. Recent studies suggest that a reduction in nitric oxide (NO) availability may be linked to EPO-induced vascular dysfunction. Furthermore, CRD per se is thought to result in a state of NO deficiency. The present study suggests that EPO may exert proatherogenic activity by augmenting the cytokine-induced expression of monocyte-chemoattractant protein-1 (MCP-1) in human umbilical vein endothelial cells (HUVECs) and by stimulating the proliferation of HUVECs and human vascular smooth muscle cells (HVSMCs). Augmentation of MCP-1 expression appears to be linked to EPO-induced downregulation of endothelial NO synthase (ecNOS). NO released from a series of synthetic donor compounds suppressed the EPO-mediated augmentation of cytokine-induced MCP-1 expression. In vitro studies revealed that EPO reduces ecNOS expression at both the protein and mRNA levels and that EPO also mediates a reduction in ecNOS enzymatic activity. These observations suggest potential mechanisms through which EPO may contribute to the development of accelerated atherosclerosis, particularly in the setting of CRD where NO availability may already be compromised.

Recombinant human erythropoietin suppresses endothelial cell apoptosis and reduces the ratio of Bax to Bcl-2 proteins in the aortas of apolipoprotein E-deficient mice.

Recent clinical trials have raised concern that therapy with recombinant human erythropoietin (EPO) may increase cardiovascular disease risk, event rate, and mortality. Endothelial cell apoptosis has been implicated in both atherogenesis and in the destabilization and rupture of atheromatous plaques. In the current study, we observed that EPO and the EPO-mimetic peptide EMP-1 markedly suppressed lipopolysaccharide-induced apoptosis in endothelial cell monolayers. Therapeutic concentrations of EPO upregulated Bcl-2 expression and concurrently diminished expression of Bax, resulting in a net decrease in the ratio of Bax to Bcl-2 protein concentrations. In vivo studies demonstrated that EPO receptor is abundantly expressed in murine aorta and that EPO treatment for 10 weeks markedly decreased the ratio of Bax to Bcl-2 protein in the aortas of apolipoprotein E-deficient mice fed a high-fat diet. To our knowledge, these data are the first to reveal a modulation of regulators of the apoptotic pathway in murine aorta by chronic EPO treatment. These observations imply that long-term administration of EPO may have the potential to affect plaque stability.

Human recombinant erythropoietin augments serum asymmetric dimethylarginine concentrations but does not compromise nitric oxide generation in mice

BACKGROUND Patients with advanced chronic renal disease (CRD) suffer from excessive morbidity and mortality due to complications of accelerated atherosclerosis. Recombinant human erythropoietin (EPO), which is routinely used to treat the anaemia present in approximately 90% of dialysis-dependent patients with end-stage renal disease, may induce vascular dysfunction by reducing nitric oxide (NO) availability. Pathophysiologic concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), are found in patients with CRD and correlate with vascular disease and cardiovascular mortality. The aim of the current study was to investigate the effect of EPO on ADMA concentrations and NO generation in vitro and in vivo. Furthermore, we wanted to study the effect of EPO on the expression of the enzymes that regulate ADMA metabolism and NO generation. METHODS Human umbilical vein endothelial cells (HUVECs) were exposed to therapeutic concentrations of EPO. The expression and metabolic activity of dimethylarginine dimethylaminohydrolase II (DDAH II), the enzyme that degrades ADMA, was evaluated. Following subcutaneous administration of EPO to Balb/c mice for 10 weeks, serum ADMA concentrations were determined. Systolic blood pressure was measured noninvasively. Urinary nitrite and nitrate (NOx) concentrations were assessed by Griess assay. Protein expression of DDAH and NOS in livers and kidneys was measured by western blotting. RESULTS EPO suppressed ADMA elaboration by HUVECs. Systolic blood pressure and serum concentrations of ADMA were significantly elevated in EPO-treated mice. The protein expression of DDAH I in the kidney and liver was upregulated while hepatic expression of DDAH II was decreased and renal DDAH II expression remained unchanged by EPO administration. However, EPO augmented urinary NOx concentrations as well as the expression of NOS 1 and NOS 2 in the kidney. CONCLUSION In spite of elevating serum ADMA concentrations, EPO does not appear to compromise overall NO generation in Balb/c mice.