Ceramide mediates age-associated increase in macrophage cyclooxygenase-2 expression

Immunosenescence and inflammaging: Conspiracies against alveolar bone turnover

OBJECTIVE

Inflammaging and immunosenescence are characteristics of senescent immune system alterations. This review provides insights into inflammaging and immunosenescence in periodontitis and focuses on the innerlink of inflammaging and immunosenescence in alveolar bone turnover from a perspective of cell-cell interaction.

METHODS

This review is conducted by a narrative approach to discuss the effect of inflammaging and immunosenescence in aging-related alveolar bone loss. A comprehensive literature research in PubMed and Google was applied to identify reports in English.

RESULTS

Inflammaging is concerned with abnormal M1 polarization and increasing circulating inflammatory cytokines, while immunosenescence involves reduced infection and vaccine responses, depressed antimicrobial function, and infiltration of aged B cells and memory T cells. TLR-mediated inflammaging and altered adaptive immunity significantly affect alveolar bone turnover and aggravate aging-related alveolar bone loss. Besides, energy consumption also plays a vital role in aged immune and skeletal system of periodontitis.

CONCLUSIONS

Senescent immune system exerts a significant function in aging-related alveolar bone loss. Inflammaging and immunosenescence interact functionally and mechanistically, which affects alveolar bone turnover. Therefore, further clinical treatment strategies targeting alveolar bone loss could be based on the specific molecular mechanism connecting inflammaging, immunosenescence, and alveolar bone turnover.

The guardians of pulmonary harmony: alveolar macrophages orchestrating the symphony of lung inflammation and tissue homeostasis

Recent breakthroughs in single-cell sequencing, advancements in cellular and tissue imaging techniques, innovations in cell lineage tracing, and insights into the epigenome collectively illuminate the enigmatic landscape of alveolar macrophages in the lung under homeostasis and disease conditions. Our current knowledge reveals the cellular and functional diversity of alveolar macrophages within the respiratory system, emphasising their remarkable adaptability. By synthesising insights from classical cell and developmental biology studies, we provide a comprehensive perspective on alveolar macrophage functional plasticity. This includes an examination of their ontology-related features, their role in maintaining tissue homeostasis under steady-state conditions and the distinct contribution of bone marrow-derived macrophages (BMDMs) in promoting tissue regeneration and restoring respiratory system homeostasis in response to injuries. Elucidating the signalling pathways within inflammatory conditions, the impact of various triggers on tissue-resident alveolar macrophages (TR-AMs), as well as the recruitment and polarisation of macrophages originating from the bone marrow, presents an opportunity to propose innovative therapeutic approaches aimed at modulating the equilibrium between phenotypes to induce programmes associated with a pro-regenerative or homeostasis phenotype of BMDMs or TR-AMs. This, in turn, can lead to the amelioration of disease outcomes and the attenuation of detrimental inflammation. This review comprehensively addresses the pivotal role of macrophages in the orchestration of inflammation and resolution phases after lung injury, as well as ageing-related shifts and the influence of clonal haematopoiesis of indeterminate potential mutations on alveolar macrophages, exploring altered signalling pathways and transcriptional profiles, with implications for respiratory homeostasis.

Vitamin D as a Shield against Aging

Aging can be seen as a physiological progression of biomolecular damage and the accumulation of defective cellular components, which trigger and amplify the process, toward whole-body function weakening. Senescence initiates at the cellular level and consists in an inability to maintain homeostasis, characterized by the overexpression/aberrant expression of inflammatory/immune/stress responses. Aging is associated with significant modifications in immune system cells, toward a decline in immunosurveillance, which, in turn, leads to chronic elevation of inflammation/oxidative stress, increasing the risk of (co)morbidities. Albeit aging is a natural and unavoidable process, it can be regulated by some factors, like lifestyle and diet. Nutrition, indeed, tackles the mechanisms underlying molecular/cellular aging. Many micronutrients, i.e., vitamins and elements, can impact cell function. This review focuses on the role exerted by vitamin D in geroprotection, based on its ability to shape cellular/intracellular processes and drive the immune response toward immune protection against infections and age-related diseases. To this aim, the main biomolecular paths underlying immunosenescence and inflammaging are identified as biotargets of vitamin D. Topics such as heart and skeletal muscle cell function/dysfunction, depending on vitamin D status, are addressed, with comments on hypovitaminosis D correction by food and supplementation. Albeit research has progressed, still limitations exist in translating knowledge into clinical practice, making it necessary to focus attention on the role of vitamin D in aging, especially considering the growing number of older individuals.

Age-associated alterations in immune function and inflammation

Immunosenescence is a term used to describe the age-related changes in the immune system. Immunosenescence is associated with complex alterations and dysregulation of immune function and inflammatory processes. Age-related changes in innate immune responses including alterations in chemotactic, phagocytic, and natural killing functions, impaired antigen presenting capacity, and dysregulated inflammatory response have been described. The most striking and best characterized feature of immunosenescence is the decline in both number and function of T cells. With age there is decreased proliferation, decreased number of antigen-naïve T cells, and increased number of antigen-experienced memory T cells. This decline in naïve T cell population is associated with impaired immunity and reduced response to new or mutated pathogens. While the absolute number of peripheral B cells appears constant with age, changes in B cell functions including reduced antibody production and response and cell memory have been described. However, the main alteration in cell-mediated function that has been reported across all species with aging is those observed in in T cell. These T cell mediated changes have been shown to contribute to increased susceptibility to infection and cancer in older adults. In addition to functional and phenotype alterations in immune cells, studies demonstrate that circulating concentrations of inflammatory mediators in older adults are higher than those of young. This low grade, chronic inflammatory state that occurs in the context of aging has been termed "inflammaging". This review will focus on age-related changes in the immune system including immunosenescence and inflammation as well as the functional consequences of these age-related alterations for the aged.

The promising roles of macrophages in geriatric hip fracture

As aging becomes a global burden, the incidence of hip fracture (HF), which is the most common fracture in the elderly population and can be fatal, is rapidly increasing, and its extremely high fatality rate places significant medical and financial burdens on patients. Fractures trigger a complex set of immune responses, and recent studies have shown that with aging, the immune system shows decreased activity or malfunctions in a process known as immune senescence, leading to disease and death. These phenomena are the reasons why elderly individuals typically exhibit chronically low levels of inflammation and increased rates of infection and chronic disease. Macrophages, which are key players in the inflammatory response, are critical in initiating the inflammatory response, clearing pathogens, controlling the innate and adaptive immune responses and repairing damaged tissues. Tissue-resident macrophages (TRMs) are widely present in tissues and perform immune sentinel and homeostatic functions. TRMs are combinations of macrophages with different functions and phenotypes that can be directly influenced by neighboring cells and the microenvironment. They form a critical component of the first line of defense in all tissues of the body. Immune system disorders caused by aging could affect the biology of macrophages and thus the cascaded immune response after fracture in various ways. In this review, we outline recent studies and discuss the potential link between monocytes and macrophages and their potential roles in HF in elderly individuals.

Understanding the role of host metabolites in the induction of immune senescence: Future strategies for keeping the ageing population healthy

Advancing age is accompanied by significant remodelling of the immune system, termed immune senescence, and increased systemic inflammation, termed inflammageing, both of which contribute towards an increased risk of developing chronic diseases in old age. Age-associated alterations in metabolic homeostasis have been linked with changes in a range of physiological functions, but their effects on immune senescence remains poorly understood. In this article, we review the recent literature to formulate hypotheses as to how an age-associated dysfunctional metabolism, driven by an accumulation of key host metabolites (saturated fatty acids, cholesterol, ceramides and lactate) and loss of other metabolites (glutamine, tryptophan and short-chain fatty acids), might play a role in driving immune senescence and inflammageing, ultimately leading to diseases of old age. We also highlight the potential use of metabolic immunotherapeutic strategies targeting these processes in counteracting immune senescence and restoring immune homeostasis in older adults. LINKED ARTICLES: This article is part of a themed issue on Inflammation, Repair and Ageing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.9/issuetoc.

Ceramide signaling in the gut

Sphingolipids are essential lipid components in the intestinal epithelial cells (IEC) along the intestinal tract. They play crucial roles in maintaining barrier integrity, regulating nutrient absorption, and acting as signaling molecules to regulate regeneration and differentiation of intestinal mucosa (Kurek et al., 2012). Ceramide is the central sphingolipid species and the precursor of all complex sphingolipids and other downstream simple intermediates like sphingosine (SPH), ceramide-1-phosphate (C-1-P), and sphingosine-1-phosphate (S-1-P). It is also a critical signaling molecule regulating numerous physiologic and pathologic processes. This review will summarize the metabolism of ceramides in the gut and their regulation in inflammatory bowel diseases and colorectal cancer.

The impact of ageing on monocytes and macrophages

Ageing is a global burden. Increasing age is associated with increased incidence of infections and cancer and decreased vaccine efficacy. This increased morbidity observed with age, is believed to be due in part to a decline in adaptive immunity, termed immunosenescence. However not all aspects of immunity decrease with age as ageing presents with systemic low grade chronic inflammation, characterised by elevated concentrations of mediators such as IL-6, TNFα and C Reactive protein (CRP). Inflammation is a strong predictor of morbidity and mortality, and chronic inflammation is known to be detrimental to a functioning immune system. Although the source of the inflammation is much discussed, the key cells which are believed to facilitate the inflammageing phenomenon are the monocytes and macrophages. In this review we detail how macrophage and monocyte phenotype and function change with age. The impact of ageing on macrophages includes decreased phagocytosis and immune resolution, increased senescent-associated markers, increased inflammatory cytokine production, reduced autophagy, and a decrease in TLR expression. With monocytes there is an increase in circulating CD16⁺ monocytes, decreased type I IFN production, and decreased efferocytosis. In conclusion, we believe that monocytes and macrophages contribute to immunosenescence and inflammageing and as a result have an important role in defective immunity with age.

TET2-Loss-of-Function-Driven Clonal Hematopoiesis Exacerbates Experimental Insulin Resistance in Aging and Obesity

Human aging is frequently accompanied by the acquisition of somatic mutations in the hematopoietic system that induce clonal hematopoiesis, leading to the development of a mutant clone of hematopoietic progenitors and leukocytes. This somatic-mutation-driven clonal hematopoiesis has been associated with an increased incidence of cardiovascular disease and type 2 diabetes, but whether this epidemiological association reflects a direct, causal contribution of mutant hematopoietic and immune cells to age-related metabolic abnormalities remains unexplored. Here, we show that inactivating mutations in the epigenetic regulator TET2, which lead to clonal hematopoiesis, aggravate age- and obesity-related insulin resistance in mice. This metabolic dysfunction is paralleled by increased expression of the pro-inflammatory cytokine IL-1β in white adipose tissue, and it is suppressed by pharmacological inhibition of NLRP3 inflammasome-mediated IL-1β production. These findings support a causal contribution of somatic TET2 mutations to insulin resistance and type 2 diabetes.

Association between Cyclooxygenase-2 and Indoleamine 2,3-Dioxygenase Expression in Breast Cancer Patients from Pakistan

Background:

Tumors use several immunosuppressive mechanisms to evade immune destruction. Cyclooxygenase-2 (COX-2) expression may be a driver of immunosuppression in breast cancer, but the mechanisms involved remain elusive. COX-2 expression induces the expression of indoleamine 2,3 dioxygenase (IDO) in tumor cells. IDO is an immunosuppressive enzyme which is involved in tumor immune escape mechanisms in breast cancer. Our aim was to evaluate the association between COX-2 and IDO expression to find evidence of immunosuppression in Pakistani breast cancer patients.

Methods:

Immunohistochemical analysis was performed to evaluate the expression of COX-2, IDO, estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) on formalin-fixed paraffin-embedded breast cancer tissues of 100 patients. Univariable and multivariable logistic regression model was used to identify the independent risk factors of COX-2.

Results:

A total of 100 patients were included with a mean age and standard deviation of 48.28 ± 11.83. A significant association was observed among COX-2, IDO, ER, PR and tumor grade. In multivariable analysis, three variables were identified as significant independent risk factors for high COX-2: IDO expression high; [adjusted odds ratio (AOR) 6.51; 95% confidence interval (CI) (2.00-21.20), p=0.001], ER; [AOR 5.62; 95% CI (1.80-17.84), p=0.002] and age [AOR 1.04; 95% CI (1.00-1.10), p=0.05] respectively.

Conclusion:

Our data showed that high IDO expression is associated with high COX-2 expression in Pakistani breast cancer patients. The co-expression of both enzymes may suggest their role in disease pathogenesis. Hence the concurrent targeting of COX-2 and IDO may be a promising therapy for breast cancer.

Sphingolipidomic Profiling of Rat Serum by UPLC-Q-TOF-MS: Application to Rheumatoid Arthritis Study

Sphingolipids (SPLs) are biologically important molecules, but the structural diversity and complexity of SPLs brings significant analytical challenges for their study. In this paper, we have developed an UPLC-Q-TOF-MS-based sphingolipidomic approach for the comprehensive identification and quantification of SPLs in rat serum. A total of 120 SPLs covering seven subcategories were identified for the first time. Method validations including linearity, sensitivity, reproducibility, and recovery were also evaluated. This method was exemplarily applied to characterize the SPL alterations in rheumatoid arthritis (RA) rats and the intervention effects of indomethacin (IDM). Partial least squares-discriminant analysis (PLS-DA) showed that the model group was well separated from the control group, whereas the IDM-treated group exhibited a trend to recover the controls. Twenty-six significantly changed SPL markers were explored, and the levels of ceramides (Cers) and their metabolites were found to be reversed by IDM treatment. These results indicate that IDM exerts anti-arthritic effects through the suppression of Cer-mediated COX-2 activation and resulting PEG₂ liberation. The present study demonstrates a promising potential of this method for the understanding of RA and the anti-arthritic mechanisms of relevant drugs.

Nutritional modulation of age-related changes in the immune system and risk of infection

The immune system undergoes some adverse alterations during aging, many of which have been implicated in the increased morbidity and mortality associated with infection in the elderly. In addition to intrinsic changes to the immune system with aging, the elderly are more likely to have poor nutritional status, which further impacts the already impaired immune function. Although the elderly often have low zinc serum levels, several manifestations commonly observed during zinc deficiency are similar to the changes in immune function with aging. In the case of vitamin E, although its deficiency is rare, the intake above recommended levels is shown to enhance immune functions in the elderly and to reduce the risk of acquiring upper respiratory infections in nursing home residents. Vitamin D is a critical vitamin in bone metabolism, and its deficiency is far more common, which has been linked to increased risk of infection as demonstrated in a number of observational studies including those in the elderly. In this review, we focus on zinc, vitamin E, and vitamin D, the 3 nutrients which are relatively well documented for their roles in impacting immune function and infection in the elderly, to discuss the findings in this context reported in both the observational studies and interventional clinical trials. A perspective will be provided based on the analysis of information under review.

Sphingolipids as Mediators in the Crosstalk between Microbiota and Intestinal Cells: Implications for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) describes different illnesses characterized by chronic inflammation of the gastrointestinal tract. Although the pathogenic mechanisms leading to IBD are poorly understood, immune system disturbances likely underlie its development. Sphingolipids (SLs) have been identified as important players and promising therapeutic targets to control inflammation in IBD. Interestingly, it seems that microorganisms of the normal gut microbiota and probiotics are involved in sphingolipid function. However, there is a great need to investigate the role of SLs as intermediates in the crosstalk between intestinal immunity and microorganisms. This review focuses on recent investigations that describe some mechanisms involved in the regulation of cytokine profiles by SLs. We also describe the importance of gut microbiota in providing signaling molecules that favor the communication between resident bacteria and intestinal cells. This, in turn, modulates the immune response in the bowel and likely in other peripheral organs. The potential of SLs and gut microbiota as targets or therapeutic agents for IBD is also discussed.

Ageing, adipose tissue, fatty acids and inflammation

A common feature of ageing is the alteration in tissue distribution and composition, with a shift in fat away from lower body and subcutaneous depots to visceral and ectopic sites. Redistribution of adipose tissue towards an ectopic site can have dramatic effects on metabolic function. In skeletal muscle, increased ectopic adiposity is linked to insulin resistance through lipid mediators such as ceramide or DAG, inhibiting the insulin receptor signalling pathway. Additionally, the risk of developing cardiovascular disease is increased with elevated visceral adipose distribution. In ageing, adipose tissue becomes dysfunctional, with the pathway of differentiation of preadipocytes to mature adipocytes becoming impaired; this results in dysfunctional adipocytes less able to store fat and subsequent fat redistribution to ectopic sites. Low grade systemic inflammation is commonly observed in ageing, and may drive the adipose tissue dysfunction, as proinflammatory cytokines are capable of inhibiting adipocyte differentiation. Beyond increased ectopic adiposity, the effect of impaired adipose tissue function is an elevation in systemic free fatty acids (FFA), a common feature of many metabolic disorders. Saturated fatty acids can be regarded as the most detrimental of FFA, being capable of inducing insulin resistance and inflammation through lipid mediators such as ceramide, which can increase risk of developing atherosclerosis. Elevated FFA, in particular saturated fatty acids, maybe a driving factor for both the increased insulin resistance, cardiovascular disease risk and inflammation in older adults.

Sphingomyelin and phosphatidylcholine contrarily affect the induction of apoptosis in intestinal epithelial cells

SCOPE

The major alimentary sources for the plasma membrane lipid sphingomyelin (SM) are dairy products, eggs, and meat. We recently reported that the SM metabolite ceramide induces cathepsin D mediated apoptosis in murine intestinal epithelial cells (IECs) and increases inflammation in acute colitis. We investigated the impact of SM and phosphatidylcholine on apoptosis in human IECs and point out BH3-interacting death agonist (BID) as link between cathepsin D and apoptosis.

METHODS AND RESULTS

HT-29 and isolated human IECs were stimulated with SM or phosphatidylcholine. SM treatment resulted in increased apoptosis. Phosphatidylcholine showed contrary effects. Western revealed higher amounts of cathepsin D and BID activation upon lipid stimulation. Western blotting revealed BID activation through SM in both an induced and a spontaneous mouse model of colitis.

CONCLUSION

Dietary phospholipids may induce or abolish apoptosis in IECs and seem to play a role in the pathogenesis of inflammatory bowel diseases. This nutritional factor might be considered when evaluating the pathogenesis of inflammatory bowel diseases. Effects of SMase- and SM treatment on inflammation in dextran sulfate sodium induced animal models of colitis and in vitro experiments are discussed as controversial. Variable sources of SM, feeding techniques, and mouse strains might play a role.

Diet-induced obesity has a differential effect on adipose tissue and macrophage inflammatory responses of young and old mice

Obesity and aging are both associated with increased inflammation in adipose tissue. In this study, we investigated effect of diet-induced obesity on inflammatory status in young and old mice. Young (2 months) and old (19 months) C57BL/6 mice were fed a low-fat (10%, LF) or high-fat (60%, HF) diet for 4.5 months. Adipose tissue from old/LF mice expressed higher levels of IL-1β, IL-6, TNFα, and cyclooxygenase-2 mRNA compared with young/LF mice. HF diet upregulated expression of all these inflammatory markers in young mice to the levels seen in the aged. Adipocytes, but not stromal vascular cells, from old/LF mice produced more IL-6, TNFα, and prostaglandin (PG)E2 than those from young/LF mice. HF diet resulted in an increase of all these markers produced by adipocytes in young, but only TNFα in old mice. PGE2 produced by peritoneal macrophages (Mϕ's) was upregulated with aging, and HF diet induced more IL-6, TNFα, and PGE2 production in young but not in old mice. Thus, HF diet/obesity induces an inflammatory state in both visceral fat cells and peritoneal Mϕ's of young mice, but not so in old mice. Together, these results suggest that HF diet-induced obesity may speed up the aging process as characterized by inflammatory status. This study also indicates that animals have a differential response, depending on their ages, to HF diet-induced obesity and inflammation. This age-related difference in response to HF diet should be considered when using inflammation status as a marker in investigating adverse health impacts of HF diet and obesity.

Avenanthramides inhibit proliferation of human colon cancer cell lines in vitro

A high intake of whole grain foods is associated with reduced risk of colon cancer, but the mechanism underlying this protection has yet to be elucidated. Chronic inflammation and associated cyclooxygenase-2 (COX-2) expression in the colon epithelium are causally related to epithelial carcinogenesis, proliferation, and tumor growth. We examined the effect of avenanthramides (Avns), unique polyphenols from oats with anti-inflammatory properties, on COX-2 expression in macrophages, colon cancer cell lines, and on proliferation of human colon cancer cell lines. We found that Avns-enriched extract of oats (AvExO) had no effect on COX-2 expression, but it did inhibit COX enzyme activity and prostaglandin E(2) (PGE(2)) production in lipopolysaccharide-stimulated mouse peritoneal macrophages. Avns (AvExO, Avn-C, and the methylated form of Avn-C (CH3-Avn-C)) significantly inhibited cell proliferation of both COX-2-positive HT29, Caco-2, and LS174T, and COX-2-negative HCT116 human colon cancer cell lines, CH3-Avn-C being the most potent. However, Avns had no effect on COX-2 expression and PGE(2) production in Caco-2 and HT29 colon cancer cells. These results indicate that the inhibitory effect of Avns on colon cancer cell proliferation may be independent of COX-2 expression and PGE(2) production. Thus, Avns might reduce colon cancer risk through inhibition of macrophage PGE(2) production and non-COX-related antiproliferative effects in colon cancer cells. Interestingly, Avns had no effect on cell viability of confluence-induced differentiated Caco-2 cells, which display the characteristics of normal colonic epithelial cells. Our results suggest that the consumption of oats and oat bran may reduce the risk of colon cancer not only because of their high fiber content but also due to Avns, which attenuate proliferation of colonic cancer cells.

Suppression of intestinal inflammation and inflammation-driven colon cancer in mice by dietary sphingomyelin: importance of peroxisome proliferator-activated receptor γ expression

Inflammation of the gastrointestinal tract increases the risk of developing colon cancer especially in younger adults. Dietary compounds are not only associated with the etiology of inflammation and colon cancer but also in their prevention. Sphingolipid metabolites have been shown to play a role in the initiation and perpetuation of inflammatory responses. In the present study, we investigated the suppression of dextran sodium sulfate-induced colitis and azoxymethane-induced colon cancer by dietary sphingomyelin (SM) in mice that lack functional peroxisome proliferator-activated receptor γ (PPAR-γ) in intestinal epithelial and immune cells. Dietary SM decreased disease activity and colonic inflammatory lesions in mice of both genotypes but more efficiently in mice expressing PPAR-γ. The increased survival and suppression of tumor formation in the SM-fed mice appeared to be independent of PPAR-γ expression in immune and epithelial cells. Using a real-time polymerase chain reaction array, we detected an up-regulation in genes involved in Th1 (interferon γ) and Th17 (interleukin [IL]-17 and IL-23) responses despite the reduced inflammation scores. However, the genes involved in Th2 (IL-4, IL-13 and IL-13ra2) and Treg (IL-10rb) anti-inflammatory responses were up-regulated in a PPAR-γ-dependent manner. In line with the PPAR-γ dependency of our in vivo findings, treatment of RAW macrophages with sphingosine increased the PPAR-γ reporter activity. In conclusion, dietary SM modulated inflammatory responses at the early stages of the disease by activating PPAR-γ, but its anticarcinogenic effects followed a PPAR-γ-independent pattern.

Ceramide in stress response

Evidence has consistently indicated that activation of sphingomyelinases and/or ceramide synthases and the resulting accumulation of ceramide mediate cellular responses to stressors such as lipopolysaccharide, interleukin 1beta, tumor necrosis factor alpha, serum deprivation, irradiation and various antitumor treatments. Recent studies had identified the genes encoding most of the enzymes responsible for the generation of ceramide and ongoing research is aimed at characterizing their individual functions in cellular response to stress. This chapter discusses the seminal and more recent discoveries in regards to the pathways responsible for the accumulation of ceramide during stress and the mechanisms by which ceramide affects cell functions. The former group includes the roles of neutral sphingomyelinase 2, serine palmitoyltransferase, ceramide synthases, as well as the secretory and endosomal/lysosomal forms of acid sphingomyelinase. The latter summarizes the mechanisms by which ceramide activate its direct targets, PKCzeta, PP2A and cathepsin D. The ability of ceramide to affect membrane organization is discussed in the light of its relevance to cell signaling. Emerging evidence to support the previously assumed notion that ceramide acts in a strictly structure-specific manner are also included. These findings are described in the context of several physiological and pathophysiological conditions, namely septic shock, obesity-induced insulin resistance, aging and apoptosis of tumor cells in response to radiation and chemotherapy.

Calorie restriction enhances T-cell-mediated immune response in adult overweight men and women

Calorie restriction (CR) enhances immune response and prolongs life span in animals. However, information on the applicability of these results to humans is limited. T-cell function declines with age. We examined effects of CR on T-cell function in humans. Forty-six overweight, nonobese participants aged 20-42 years were randomly assigned to 30% or 10% CR group for 6 months. Delayed-type hypersensitivity (DTH), T-cell proliferation (TP), and prostaglandin E(2) (PGE(2)) productions were determined before and after CR. DTH and TP to T-cell mitogens were increased in both groups over baseline (p < or = .019). However, number of positive responses to DTH antigens (p = .016) and TP to anti-CD3 reached statistical significance only after 30% CR (p = .001). Lipopolysaccharide-stimulated PGE(2) was reduced in both groups but reached statistical significance after 30% CR (p < or = .029). These results, for the first time, show that 6-month CR in humans improves T-cell function.

Nutrition and age-associated inflammation: implications for disease prevention

Accumulating evidence suggests that aging is associated with dysregulated immune and inflammatory responses. Investigation into the cellular and molecular mechanisms underlying this phenomenon suggests that an up-regulated cyclooxygenase (COX)-2 expression, and resulting increase in production of prostaglandin E(2) (PGE(2)), is a critical factor. Macrophages from old mice have significantly higher levels of PGE(2) production compared with those from young mice, a result of increased COX-2 expression and protein levels leading to increased COX enzyme activity. Furthermore, studies suggest that the age-associated increase in macrophage PGE(2) production is due to ceramide-induced up-regulation of nuclear factor-kappa B activation. Such processes may also occur in cell types other than macrophages, lending further insight into potential mechanisms of age-related diseases. Moreover, the excess PGE(2) induces harmful effects in other cell types such as T cells and adipocytes through the negative crosstalk between macrophages with other cells, resulting in further increased susceptibility to diseases. Nutrient/dietary medications, such as antioxidants and certain lipids have suggested a promising route to reduce the age-related increase in COX activity and PGE(2) production that is associated with several disease states.

Role of neutral sphingomyelinases in aging and inflammation

Aging is characterized by changes in the organism's immune functions and stress response, which in the elderly leads to increased incidence of complications and mortality following inflammatory stress. Alterations in the neuro-endocrine axes and overall decline in the immune system play an essential role in this process. Overwhelming evidence however suggests that many cellular cytokine signaling pathways are also affected, thus underscoring the idea that both, "cellular" and "systemic" changes contribute to aging. IL-1beta for example, induces more potent cellular responses in hepatocytes isolated from aged animals then in hepatocytes from young rats. This phenomenon is referred to as IL-1b hyperresponsiveness and is linked to abnormal regulation of various acute phase proteins during aging.Evidence has consistently indicated that activation of neutral sphingomyelinase and the resulting accumulation of ceramide mediate cellular responses to LPS, IL-1beta, and TNFalpha in young animals. More recent studies identified the cytokine-inducible neutral sphingomyelinase with nSMase2 (smpd3) that is localized in the plasma membrane and mediates cellular responses to IL-1beta and TNFalpha. Intriguingly, constitutive up-regulation of nSMase2 occurs in aging and it underlies the hepatic IL-1b hyperresponsiveness. The increased activity of nSMases2 in aging is caused by a substantial decline in hepatic GSH content linking thereby oxidative stress to the onset of pro-inflammatory state in liver. nSMase2 apparently follows a pattern of regulation consisting with "developmental-aging" continuum, since in animal models of delayed aging, like calorie-restricted animals, the aging-associated changes in NSMase activity and function are reversed.

Age-associated changes in immune and inflammatory responses: impact of vitamin E intervention

Aging is associated with dysregulated immune and inflammatory responses. Declining T cell function is the most significant and best-characterized feature of immunosenescence. Intrinsic changes within T cells and extrinsic factors contribute to the age-associated decline in T cell function. T cell defect seen in aging involves multiple stages from early receptor activation events to clonal expansion. Among extrinsic factors, increased production of T cell-suppressive factor PGE(2) by macrophages (Mphi) is most recognized. Vitamin E reverses an age-associated defect in T cells, particularly naïve T cells. This effect of vitamin E is also reflected in a reduced rate of upper respiratory tract infection in the elderly and enhanced clearance of influenza infection in a rodent model. The T cell-enhancing effect of vitamin E is accomplished via its direct effect on T cells and indirectly by inhibiting PGE(2) production in Mphi. Up-regulated inflammation with aging has attracted increasing attention as a result of its implications in the pathogenesis of diseases. Increased PGE(2) production in old Mphi is a result of increased cyclooxygenase 2 (COX-2) expression, leading to higher COX enzyme activity, which in turn, is associated with the ceramide-induced up-regulation of NF-kappaB. Similar to Mphi, adipocytes from old mice have a higher expression of COX-2 as well as inflammatory cytokines IL-1beta, IL-6, and TNF-alpha, which might also be related to elevated levels of ceramide and NF-kappaB activation. This review will discuss the above age-related immune and inflammatory changes and the effect of vitamin E as nutritional intervention with a focus on the work conducted in our laboratory.

Age-associated inflammatory changes: role of nutritional intervention

Accumulating evidence suggests that aging is associated with dysregulated immune and inflammatory responses. Investigation into the cellular and molecular mechanisms underlying this phenomenon suggests that an up-regulated cyclooxygenase (COX)-2 expression, and resulting increase in production of prostaglandin E2 (PGE2), is a critical factor. Macrophages from old mice have significantly higher levels of PGE2 production compared with those from young mice, a result of increased COX-2 expression and protein levels leading to increased COX enzyme activity. Further, it is possible that the age-associated increase in macrophage PGE2 production is due to ceramide-induced up-regulation of nuclear factor-kappa B activation. Such processes may also occur in cell types other than macrophages, lending further insight into potential mechanisms of age-related disease. More research is necessary to determine the efficacy of nutrient/dietary modifications, such as antioxidants and lipids, for reducing the age-related increase in COX activity and PGE2 production that are associated with several disease states.

Aging up-regulates expression of inflammatory mediators in mouse adipose tissue

Obesity is a leading risk factor for type 2 diabetes (T2D). Aging is associated with an increase in T2D incidence, which is not totally explained by the much lower prevalence of obesity in the elderly. Low-grade inflammation in adipose tissue (AT) contributes to insulin resistance and T2D. Thus, we determined whether inflammatory responses are up-regulated with age in AT. The results showed that visceral AT from old C57BL mice had significantly higher mRNA expression of the proinflammatory cytokines IL-1beta, IL-6, TNF-alpha, and COX-2 and lower expression of anti-inflammatory PPAR-gamma than those of young mice. We further showed that adipocytes (AD) and not stromal vascular cells including macrophages (Mphi) were the cells responsible for this higher inflammatory state of the aged AT, suggesting that the age-associated increase in AT inflammation is distinguished from that seen in obesity, in which Mphi are the main contributors. However, peritoneal Mphi of either age (young or old) produced more TNF-alpha and IL-6 after incubation in old AD-conditioned medium compared with young AD-conditioned medium. This suggests that in addition to producing more inflammatory cytokines, AD from old mice induce a higher inflammatory response in other cells. Sphingolipid ceramide was higher in old compared with young AD. Reducing ceramide levels or inhibiting NF-kappaB activation decreased cytokine production, whereas the addition of ceramide increased cytokine production in young AD to a level comparable to that seen in old AD, suggesting that ceramide-induced activation of NF-kappaB plays a key role in AT inflammation.

Aging in rat causes hepatic hyperresposiveness to interleukin-1beta which is mediated by neutral sphingomyelinase-2

The process of aging has recently been shown to substantially affect the ability of cells to respond to inflammatory challenges. We demonstrate that aging leads to hepatic hyperresponsiveness to interleukin 1beta (IL-1beta), and we examine the factors that could be responsible for this phenomenon. IL-1beta-induced phosphorylation of c-jun N-terminal kinase (JNK) in hepatocytes isolated from aged rats was 3 times more potent than that in hepatocytes from young rats. Moreover, JNK was activated by substantially lower doses of IL-1beta. These age-related changes in JNK phosphorylation correlated with diminished IL-1beta-induced degradation of interleukin-1 receptor-associated kinase-1 (IRAK-1). Expression levels of IL1beta receptor I, total JNK, IRAK-1, and transforming growth factor-beta-activated kinase-1 (TAK-1) were not affected by aging. However, increased neutral sphingomyelinase activity was observed in hepatocytes from old animals, which we show is caused by induction of the plasma membrane localized neutral sphingomyelinase-2 (NSMase-2). We provide evidence that NSMase-2 is both required and sufficient for the onset of IL-1beta hyperresponsiveness during aging. Overexpression of NSMase-2 in hepatocytes from young rats leads both to a reduction in IRAK-1 degradation and potentiation of JNK phosphorylation, mimicking that seen in hepatocytes from old animals. More importantly, inhibition of NSMase activity in hepatocytes from aged rats using either scyphostatin or short interfering ribonucleic acid (siRNA) leads to reversion to the "young" phenotype of IL-1beta response.

CONCLUSION

These results show that the process of aging causes increased basal NSMase-2 activity in hepatocytes, which in turn leads to IRAK-1 stabilization, JNK potentiation, and ultimately IL-1beta hyperresponsiveness.

Regulation of neutral sphingomyelinase-2 by GSH: a new insight to the role of oxidative stress in aging-associated inflammation

Oxidative stress and inflammation are fundamental for the onset of aging and appear to be causatively linked. Previously, we reported that hepatocytes from aged rats, compared with young rats, are hyperresponsive to interleukin-1beta (IL-1beta) stimulation and exhibit more potent c-Jun N-terminal kinase (JNK) activation and attenuated interleukin-1 receptor-associated kinase-1 (IRAK-1) degradation. An age-related increase in the activity of neutral sphingomyelinase-2 (NSMase-2), a plasma membrane enzyme, was found to be responsible for the IL-1beta hyperresponsiveness. The results reported here show that increased NSMase activity during aging is caused by a 60-70% decrease in hepatocyte GSH levels. GSH, at concentrations typically found in hepatocytes from young animals, inhibits NSMase activity in a biphasic dose-dependent manner. Inhibition of GSH synthesis in young hepatocytes activates NSMase, causing increased JNK activation and IRAK-1 stabilization in response to IL-1beta, mimicking the hyperresponsiveness typical for aged hepatocytes. Vice versa, increased GSH content in hepatocytes from aged animals by treatment with N-acetylcysteine inhibits NSMase activity and restores normal IL-1beta response. Importantly, the GSH decline, NSMase activation, and IL-1beta hyperresponsiveness are not observed in aged, calorie-restricted rats. In summary, this report demonstrates that depletion of cellular GSH during aging plays an important role in regulating the hepatic response to IL-1beta by inducing NSMase-2 activity.

Ceramide attenuates hypoxic cell death via reactive oxygen species signaling

We have previously demonstrated that tumor necrosis factor alpha (TNFalpha), a cytokine known to be induced by ischemia, independently promotes preconditioning in part via ceramide generation. As reactive oxygen species (ROS) signaling is evoked by ischemic preconditioning, by TNFalpha and by ceramide we reasoned that ceramide-induced preconditioning is ROS-mediated. Fibroblastic L-cells were subjected to 8 hours simulated ischemia and were preconditioned by pretreatment with cell permeable c2 ceramide (1 microM) with or without the antioxidant N-mercaptopropionyl glycine (MPG; 1 mM). Pretreatment with ceramide reduced lactate dehydrogenase release at the end of the simulated ischemia but this cytoprotective effect was lost in the presence of MPG. Concurrent temporal ROS generation was measured using confocal microscopy on cells stained with dichlorofluorescein diacetate (DCF-DA). Ceramide increased ROS production after 30 minutes and this induction was decreased by MPG. Incubation of ceramide with cyclooxygenase-2 inhibitor, NS 398 (10 microM), or with a mitochondrial respiratory chain inhibitor, rotenone (10 microM) reduced the cytoprotective effect of ceramide in parallel with a partial diminution in ROS generation. In contrast, inhibition of other ROS-producing systems including nitric oxide synthase, xanthine oxidase, or NADPH oxidase failed to modulate ceramide-induced cytoprotection. Collectively, these data demonstrate that ceramide induces a cell survival program through ROS signaling activated, in part, via cyclooxygenase and the mitochondrial respiratory chain.

The molecular inflammatory process in aging

Emerging pathological evidence indicates that major chronic aging-related diseases such as atherosclerosis, arthritis, dementia, osteoporosis, and cardiovascular diseases, are inflammation-related. In this review, inflammation is examined as a possible underlying basis for the molecular alterations that link aging and age-related pathological processes. A proposal for the molecular inflammation hypothesis of the aging views the redox derangement that occurs during aging as the major factor for increased risk for age-related inflammation. Accumulated data strongly indicate the activation of redox-sensitive transcription factors and dysregulated gene expression under the age-related oxidative stress seems to be the major culprits. Key players involved in the inflammatory process are the age-related upregulation of NF-kappaB, IL-1beta, IL-6, TNFalpha, cyclooxygenase-2, adhesion molecules, and inducible NO synthase. Furthermore, data are presented on the molecular events involved in age-related NF-kappaB activation and phosphorylation by IkappaB kinase/NIK and MAPKs. Experimental data on anti-aging calorie restriction (CR) for its antiinflammatory efficacy by suppressing the upregulated proinflammatory mediators will be reviewed. Also, the involvement of another super family of transcription factors, PPARs (PPARalpha, gamma) as regulators of proinflammatory responses and NF-kappaB signaling pathway is described as well as a discussion on the physiological significance of a well-maintained balance between NF-kappaB and PPARs.

Vitamin E and immune response in the aged: molecular mechanisms and clinical implications

Nutritional status has been indicated as a contributing factor to age-related dysregulation of the immune response. Vitamin E, a lipid-soluble antioxidant vitamin, is important for normal function of the immune cells. The elderly are at a greater risk for vitamin E intake that is lower than recommended levels. Vitamin E supplementation above currently recommended levels has been shown to improve immune functions in the aged including delayed-type hypersensitivity skin response and antibody production in response to vaccination, which was shown to be mediated through increased production of interleukin (IL)-2, leading to enhanced proliferation of T cells, and through reduced production of prostaglandin E(2), a T-cell suppressive factor, as a result of a decreased peroxynitrite formation. Vitamin E increased both cell-dividing and IL-producing capacities of naive T cells, but not memory T cells. The vitamin E-induced enhancement of immune functions in the aged was associated with significant improvement in resistance to influenza infection in aged mice and a reduced risk of acquiring upper respiratory infections in nursing home residents. Further studies are needed to determine the signaling mechanisms involved in the upregulation of naive T-cell function by vitamin E as well as the specific mechanisms involved in reduction of risk for upper respiratory infections.

Molecular mechanisms of tumor necrosis factor-alpha-mediated plasminogen activator inhibitor-1 expression in adipocytes

Increased expression of plasminogen activator inhibitor -1 (PAI-1) in adipose tissues is thought to contribute to both the cardiovascular and metabolic complications associated with obesity. Tumor necrosis factor alpha (TNF-alpha) is chronically elevated in adipose tissues of obese rodents and humans and has been directly implicated to induce PAI-1 in adipocytes. In this study, we used 3T3-L1 adipocytes to examine the mechanism by which TNF-alpha up-regulates PAI-1 in the adipocyte. Acute (3 h) and chronic (24 h) exposure of 3T3-L1 adipocytes to TNF-alpha induces PAI-1 mRNA by increasing the rate of transcription of the PAI-1 gene, and de novo protein synthesis is not required for this process. Although the p44/42 and PKC signaling pathways appear to be significant in the induction of PAI-1 mRNA in response to acute treatment with TNF-alpha, the more dramatic induction of PAI-1 mRNA observed in response to chronic exposure of adipocytes to TNF-alpha was mediated by these and additional signaling molecules, including p38, PI3-kinase, tyrosine kinases, and the transcription factor NF-kappaB. Moreover, the dramatic increase in PAI-1 observed after chronic exposure of adipocytes to TNF-alpha was accompanied by increased metabolic insulin resistance. Finally, we demonstrate that the PKC pathway is also central for PAI-1 induction in response to insulin and transforming growth factor-beta (TGF-beta), two additional molecules which are elevated in obesity and shown to directly induce PAI-1 in the adipocyte. The understanding of the mechanism of regulating PAI-1 expression in the adipocytes at the molecular level provides new insight to help identify novel targets in fighting the pathological complications of obesity.

Expression of COX-2 is increased with age in papillary thyroid cancer

AIMS

To study cyclooxygenase-2 (COX-2) and matrix metalloproteinase-2 (MMP-2) expression in papillary thyroid cancer (PTC). Expression of COX-2 is elevated in various human tumours and it has an important role in carcinogenesis. MMP-2 is also an important component of the metastatic potential of tumours. In PTC the most important factor affecting survival is age, but it is poorly understood why older PTC patients have a worse prognosis.

METHODS AND RESULTS

This retrospective study comprised 108 patients with PTC, and we compared patients who were either younger than 35 (n = 59) or older than 55 (n = 49). Paraffin-embedded tumour samples were analysed for COX-2 and MMP-2 protein expression using immunohistochemistry. High (scores 2-3) COX-2 immunostaining was observed in 38/108 (35%) of the tumours, and COX-2 expression was significantly (P = 0.002) higher in the older age group (25/49; 51%) than in the young one (13/59; 22%).

CONCLUSIONS

Our study shows that COX-2 expression increases with age. It is possible that the age-related increase in COX-2 expression could explain the more aggressive behaviour of PTC in the older age group compared with the young one.

Mechanism of age-associated up-regulation in macrophage PGE2 synthesis

Many physiological functions of the body change during the aging process. Dysregulated immune and inflammatory responses have been well documented in both humans and animals. The investigation into the cellular and molecular mechanism underlying these disorders has provided compelling evidence that up-regulated cyclooxygenase (COX)-2 and its product, particularly prostaglandin (PG)E2, play a critical role in the age-associated dysregulation of the immune and inflammatory responses. In particular, several studies have shown that increased PGE2 production in old macrophages (Mphi) contributes to the suppression of T cell function with aging. Furthermore, interventions targeted at decreasing PGE2 production have been shown to enhance T cell-mediated function. COX-2 and its catalytic products are also suggested to play a key role in age-related neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Administration of anti-inflammatory drugs which inhibit COX activity has been shown, by some investigators, to be beneficial in preventing and treating these diseases. It is, thus, important to understand the underlying mechanisms of age-related COX-2 up-regulation and to delineate the factors, which contribute to this age-related change. This review focuses on the regulation of PGE2 production in murine Mphi; the age-associated changes in COX-2 expression; and its implication for certain disorders observed in the aged immune system and brain. Increased PGE2 production has been shown to be mainly due to an increase in COX activity, which is, in turn, due to an increase in COX-2 protein and mRNA expression. Elevated COX-2 mRNA represents a higher transcription rate rather than an altered stability of COX-2 mRNA. Upon stimulation, Mphi from old mice generate more ceramide, a sphingolipid, than those from young mice. Ceramide has been shown to induce, by itself, and also augment, LPS-stimulated COX-2 expression and PGE2 production. Several lines of evidence indicate that the higher ceramide levels in old Mphi are an important contributor to the age-associated up-regulation of COX-2 in Mphi. Ceramide up-regulates COX-2 transcription by increasing activation of transcription factor NF-kappaB. Further understanding of molecular mechanisms involved in COX-2 up-regulation will help in delineating fundamental age-related changes, which lead to the development of immune and neurological disorders in the aged.

Expression of interleukin-6 is greater in preadipocytes than in adipocytes of 3T3-L1 cells and C57BL/6J and ob/ob mice

Inflammation plays a major role in the development of chronic diseases such as cardiovascular disease and Type 2 diabetes. Further, it was demonstrated that obese animals and humans have significantly higher levels of circulating proinflammatory cytokines, such as interleukin-6 (IL-6). The aim of this study was to determine whether adipose tissue could be a major source of circulating IL-6 in leptin-deficient obese (ob/ob) mice by comparing the expression of IL-6 in different tissues of ob/ob mice. Our secondary goal was to determine whether preadipocytes are the source of adipose tissue IL-6. The ob/ob mice had higher levels of plasma IL-6 (P < 0.05) and adipose tissue IL-6 mRNA (P < 0.05) compared with lean mice. Interestingly, IL-6 mRNA levels of liver and spleen were not different between ob/ob and lean mice, whereas adipose tissue IL-6 mRNA levels were higher in the ob/ob mice compared with lean mice (P < 0.05). In addition, we showed that IL-6 secretion from the adipose tissue stromal vascular fraction cells was higher than that from fully differentiated adipocytes (P < 0.001). We further demonstrated that 3T3-L1 preadipocytes had significantly higher levels of lipopolysaccharide (LPS)-stimulated IL-6 mRNA and IL-6 secretion than differentiated 3T3-L1 adipocytes. Taken together, these data suggest that adipose tissue and preadipocytes from the adipose tissue stromal vascular fraction may contribute significantly to the increased plasma IL-6 levels in ob/ob mice.

Evidence against the involvement of oxidative stress in fatty acid inhibition of insulin secretion

Prolonged exposure to elevated levels of fatty acids adversely affects pancreatic beta-cell function. Here we investigated 1) whether ceramide synthesis, which we reported to mediate fatty acid inhibition of insulin gene expression, also inhibits insulin secretion and 2) whether fatty acid inhibition of insulin secretion involves the generation of reactive oxygen species (ROS), nitric oxide (NO), or prostaglandin E(2) (PGE(2)). A 72-h culture of islets in the presence of palmitate or oleate resulted in a marked decrease in glucose-induced insulin release assessed in 1-h static incubations. This effect was reproduced by exogenous diacylglycerol, but not by a cell-permeable analog of ceramide. Culture in the presence of fatty acids was not associated with an increase in intracellular peroxide or NO levels, neither was insulin secretion restored by antioxidants or an inhibitor of NO production. Exposure to fatty acids led to an increase in PGE(2) release, but an inhibitor of cyclooxygenase 2 was unable to prevent fatty acid inhibition of insulin secretion. These results indicate that fatty acid inhibition of insulin secretion 1) is not mediated by de novo ceramide synthesis, ROS, NO, or PGE(2), and 2) is likely to be caused by the generation of signals or metabolites downstream of diacylglycerol.

Differential T-cell activation by B7-1 expression

T-cell receptor-mediated T-cell activation requires cosimulation signal, which can be provided by B7-1 molecule. Our previous study demonstrated that the coexpression of a covalent peptide/major histocompatibility complex class II molecule complex and costimulatory molecule B7-1 by recombinant adenovirus leads to synergy in peptide-specific T-cell activation. However, the viral antigen-specific T-cell activation is not enhanced by B7-1 expressed by the adenovirus. To verify the differential T cell activation by B7-1 and investigate its underlying mechanisms, we constructed an adenovirus coexpressing a covalent complex of hen egg lysozyme peptide/I-Ak (HEL46-61/I-Ak) and B7-1 in the present study. In vivo studies revealed that HEL46-61-specific T-cell response, but not viral antigen-specific T-cell response, was enhanced by B7-1 expression mediated by the adenovirus, suggesting that exogenous B7-1 expression may regulate T-cell response to these two different antigens through distinct mechanisms. Furthermore, our results revealed that antigen-presenting cells were not susceptible to adenovirus infection in vivo. Based on these findings, the possible mechanism of differential B7-1 costimulation on peptide-specific and viral antigen-specific T-cell activation is discussed.

Ceramide-induced and age-associated increase in macrophage COX-2 expression is mediated through up-regulation of NF-kappa B activity

We have shown that the age-associated increase in lipopolysaccharide (LPS)-stimulated macrophages (M phi) prostaglandin E(2) (PGE(2)) production is because of ceramide-induced up-regulation of cyclooxygenase (COX)-2 transcription that leads to increased COX-2 expression and enzyme activity. To determine the mechanism of the age-related and ceramide-dependent increase in COX-2 transcription, we investigated the role of various transcription factors involved in COX-2 gene expression. The results showed that LPS-initiated activations of both consensus and COX-2-specific NF-kappa B, but not AP-1 and CREB, were significantly higher in M phi from old mice than those from young mice. We further showed that the higher NF-kappa B activation in old M phi was because of greater I kappa B degradation in the cytoplasm and p65 translocation to the nucleus. An I kappa B phosphorylation inhibitor, Bay 11-7082, inhibited NF-kappa B activation, as well as PGE(2) production, COX activity, COX-2 protein, and mRNA expression in both young and old M phi. Similar results were obtained by blocking NF-kappa B binding activity using a NF-kappa B decoy. Furthermore, NF-kappa B inhibition resulted in significantly greater reduction in PGE(2) production and COX activity in old compared with young M phi. Addition of ceramide to the young M phi, in the presence or absence of LPS, increased NF-kappa B activation in parallel with PGE(2) production. Bay 11-7082 or NF-kappa B decoy prevented this ceramide-induced increase in NF-kappa B binding activity and PGE(2) production. These findings strongly suggest that the age-associated and ceramide-induced increase in COX-2 transcription is mediated through higher NF-kappa B activation, which is, in turn, because of a greater I kappa B degradation in old M phi.

Potentiation of lipopolysaccharide-inducible cyclooxygenase 2 expression by C2-ceramide via c-Jun N-terminal kinase-mediated activation of CCAAT/enhancer binding protein beta in macrophages

Ceramide, formed by sphingomyelinase, is involved in the expression of cyclooxygenase-2 (COX-2). This study examines the effect of C2-ceramide (C2), a cell-permeable ceramide analog, on the lipopolysaccharide (LPS)-inducible COX-2 expression and signaling pathways. C2 did not induce COX-2 but potentiated LPS-inducible COX-2 expression in Raw264.7 cells, whereas dihydro-C2 was inactive. Treatment of cells with C2 notably increased LPS-inducible CCAAT/enhancer binding protein (C/EBP) DNA binding. Antibody supershift experiments revealed that LPS-induced C/EBP DNA binding activity depended on C/EBP beta and C/EBP delta but not C/EBP alpha, C/EBP epsilon or CBP/p300. C/EBP beta contributed to C2-enhanced DNA binding activity. 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl) 1H-imidazole (SB203580), a p38 kinase inhibitor, completely inhibited LPS-inducible and C2-potentiated LPS-inducible COX-2 expression. Enhancement of LPS-inducible COX-2 expression and C/EBP DNA binding by C2 was abrogated in dominant-negative mutant of JNK1 [JNK1(-)] cells. 2'-Amino-3'-methoxyflavone (PD98059) or stable transfection with dominant-negative mutant of MKK1 decreased COX-2 induction by LPS but failed to inhibit C2-enhanced LPS induction of COX-2. Transfection with dominant-negative mutant of C/EBP inhibited the ability of C2 to potentiate the induction of COX-2 by LPS. In LPS-treated cells, C2 enhanced both the nuclear translocation and the expression of LPS-inducible C/EBP beta with an increase in AP-1 DNA binding activity. These enhancements were abolished by JNK1(-) transfection. AP-1 decoy oligonucleotide suppressed C2-potentiated C/EBP beta expression, indicating that AP-1 was responsible for C2-mediated C/EBP beta expression. These results demonstrate that C2 increases C/EBP beta-mediated COX-2 induction by LPS and that the pathway of JNK1 but not ERK1/2 is responsible for C/EBP beta activation involving activator protein-1-mediated enhanced C/EBP beta expression.