Repurposing SGLT2 inhibitors for autoimmune diseases? YES, WE MAY!

T cells play a key role in driving autoimmunity, with alterations in metabolism powering their effector function. In the July 11 issue of Cell Metabolism, Jenkins et al.1 describe how a type 2 diabetes drug, canagliflozin, can be repurposed for the treatment of autoimmune disorders through metabolic reprogramming of the T cell response.

Omega-3 polyunsaturated fatty acids reverse the impact of western diets on regulatory T cell responses through averting ceramide-mediated pathways.

Western diet (WD), high in sugar and fat, promotes obesity and associated chronic low-grade pro-inflammatory environment, leading to impaired immune function, reprogramming of innate and adaptive immune cells, and development of chronic degenerative diseases, including cardiovascular disease. Increased concentrations of circulating and tissue ceramides contribute to inflammation and cellular dysfunction common in immune metabolic and cardiometabolic disease. Therefore, ceramide-lowering interventions have been considered as strategies to improve adipose tissue health. Here, we report the ability of omega-3 polyunsaturated fatty acids (n-3PUFA) to attenuate inflammatory phenotypes promoted by WD, through ceramide-dependent pathways. Using an animal model, we show that enrichment of WD diet with n-3PUFA, reduced the expression of ceramide synthase 2 (CerS2), and lowered the concentration of long-chain ceramides (C23-C26) in plasma and adipose tissues. N-3PUFA also increased prevalence of the anti-inflammatory CD4+Foxp3+ and CD4+Foxp3+CD25+ Treg subtypes in lymphoid organs. The CerS inhibitor FTY720 mirrored the effect of n-3PUFA. Treatment of animal and human T cells with ceramide C24 in vitro, reduced CD4+Foxp3+ Treg polarisation and IL-10 production, and increased IL-17, while it decreased Erk and Akt phosphorylation downstream of T cell antigen receptors (TCR). These findings suggest that molecular mechanisms mediating the adverse effect of ceramides on regulatory T lymphocytes, progress through reduced TCR signalling. Our findings suggest that nutritional enrichment of WD with fish oil n-3PUFA can partially mitigate its detrimental effects, potentially improving the low-grade inflammation associated with immune metabolic disease. Compared to pharmacological interventions, n-3PUFA offer a simpler approach that can be accommodated as lifestyle choice.

Macroautophagy in lymphatic endothelial cells inhibits T cell-mediated autoimmunity.

Lymphatic endothelial cells (LECs) present peripheral tissue antigens to induce T cell tolerance. In addition, LECs are the main source of sphingosine-1-phosphate (S1P), promoting naive T cell survival and effector T cell exit from lymph nodes (LNs). Autophagy is a physiological process essential for cellular homeostasis. We investigated whether autophagy in LECs modulates T cell activation in experimental arthritis. Whereas genetic abrogation of autophagy in LECs does not alter immune homeostasis, it induces alterations of the regulatory T cell (T reg cell) population in LNs from arthritic mice, which might be linked to MHCII-mediated antigen presentation by LECs. Furthermore, inflammation-induced autophagy in LECs promotes the degradation of Sphingosine kinase 1 (SphK1), resulting in decreased S1P production. Consequently, in arthritic mice lacking autophagy in LECs, pathogenic Th17 cell migration toward LEC-derived S1P gradients and egress from LNs are enhanced, as well as infiltration of inflamed joints, resulting in exacerbated arthritis. Our results highlight the autophagy pathway as an important regulator of LEC immunomodulatory functions in inflammatory conditions.

Unwrapping the mechanisms of ceramide and fatty acid-initiated signals leading to immune-inflammatory responses in obesity.

Obesity is considered a global epidemic developed in part as a consequence of the overconsumption of high fat diets. One of the main negative outcomes of obesity is the development of low-grade chronic systemic inflammation, induced by dysregulated immune responses, which can lead to multiple obesity-related diseases. Ceramides are a group of bioactive lipids known to be elevated in obesity and obesity-associated conditions, including cardiovascular disease and type II diabetes. Ceramides may be key players in promoting an obesity-induced inflammatory environment due to their ability to activate key pathways such as Toll-like receptor 4 (TLR4) and NLR pyrin domain containing receptor 3 (Nlrp3), while studies have shown that inhibition of ceramide synthesis gives rise to an anti-inflammatory environment. N-3 polyunsaturated fatty acids (n-3 PUFA) have been of interest due to their anti-inflammatory actions and shown to have beneficial effects in obesity-related diseases. This review will highlight the impact of ceramides in promoting an obesity-induced inflammatory microenvironment and discuss how n-3 PUFA could potentially counteract these responses and have a regulatory effect promoting immune homeostasis.

Omega-3 polyunsaturated fatty acids impinge on CD4+ T cell motility and adipose tissue distribution via direct and lipid mediator-dependent effects.

AIMS: Adaptive immunity contributes to the pathogenesis of cardiovascular metabolic disorders (CVMD). The omega-3 polyunsaturated fatty acids (n-3PUFA) are beneficial for cardiovascular health, with potential to improve the dysregulated adaptive immune responses associated with metabolic imbalance. We aimed to explore the mechanisms through which n-3PUFA may alter T cell motility and tissue distribution to promote a less inflammatory environment and improve lymphocyte function in CVMD. METHODS AND RESULTS: Using mass spectrometry lipidomics, cellular, biochemical, and in vivo and ex vivo analyses, we investigated how eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the main n-3PUFA, modify the trafficking patterns of activated CD4+ T cells. In mice subjected to allogeneic immunization, a 3-week n-3PUFA-enriched diet reduced the number of effector memory CD4+ T cells found in adipose tissue, and changed the profiles of eicosanoids, octadecanoids, docosanoids, endocannabinoids, 2-monoacylglycerols, N-acyl ethanolamines, and ceramides, in plasma, lymphoid organs, and fat tissues. These bioactive lipids exhibited differing chemotactic properties when tested in chemotaxis assays with activated CD4+ T cells in vitro. Furthermore, CD4+ T cells treated with EPA and DHA showed a significant reduction in chemokinesis, as assessed by trans-endothelial migration assays, and, when implanted in recipient mice, demonstrated less efficient migration to the inflamed peritoneum. Finally, EPA and DHA treatments reduced the number of polarized CD4+ T cells in vitro, altered the phospholipid composition of membrane microdomains and decreased the activity of small Rho GTPases, Rhoα, and Rac1 instrumental in cytoskeletal dynamics. CONCLUSIONS: Our findings suggest that EPA and DHA affect the motility of CD4+ T cells and modify their ability to reach target tissues by interfering with the cytoskeletal rearrangements required for cell migration. This can explain, at least in part, the anti-inflammatory effects of n-3PUFA supporting their potential use in interventions aiming to address adipocyte low-grade inflammation associated with cardiovascular metabolic disease.

Macroautophagy in Dendritic Cells Controls the Homeostasis and Stability of Regulatory T Cells.

Regulatory T cells (Tregs) play a crucial role in controlling autoimmune and inflammatory responses. Recent studies have demonstrated that dendritic cells (DCs) contribute to the homeostasis of peripheral Tregs. Autophagy, a critical pathway for cellular homeostasis, is active in DCs and is upregulated in different inflammatory conditions. We have shown that Tregs are expanded and have phenotypic alterations and impaired suppressive functions in mice with autophagy-deficient DCs. RNA profiling of Tregs revealed that autophagy in DCs is required to stabilize Treg expression signatures. This phenotype is linked to the downregulation of ICOS-Ligand expression in autophagy-deficient DCs, a consequence of the accumulation of ADAM10, the metalloproteinase responsible for its cleavage. Upon inflammation, in antigen-induced arthritis, mice with autophagy-deficient DCs exhibit increased synovial inflammation and cartilage and bone erosion correlating with Treg-to-Th17 conversion. Our data reveal a mechanism that couples autophagy deficiency in DCs to the function, homeostasis, and stability of Tregs.

Macroautophagy Proteins Control MHC Class I Levels on Dendritic Cells and Shape Anti-viral CD8(+) T Cell Responses.

The macroautophagy machinery has been implicated in MHC class II restricted antigen presentation. Here, we report that this machinery assists in the internalization of MHC class I molecules. In the absence of the autophagy factors Atg5 and Atg7, MHC class I surface levels are elevated due to decreased endocytosis and degradation. Internalization of MHC class I molecules occurs less efficiently if AAK1 cannot be recruited via Atg8/LC3B. In the absence of Atg-dependent MHC class I internalization, dendritic cells stimulate CD8(+) T cell responses more efficiently in vitro and in vivo. During viral infections, lack of Atg5 results in enhanced influenza- and LCMV-specific CD8(+) T cell responses in vivo. Elevated influenza-specific CD8(+) T cell responses are associated with better immune control of this infection. Thus, the macroautophagy machinery orchestrates T cell immunity by supporting MHC class II but compromises MHC class I restricted antigen presentation.

Retinal Pigment Epithelial Cell Apoptosis is Influenced by a Combination of Macrophages and Soluble Mediators Present in Age-Related Macular Degeneration.

PURPOSE: Age-related macular degeneration (AMD) is one of the leading causes of blindness in the elderly population aged ≥60 years. Previous studies have shown that retinal pigment epithelial cell (RPE) degeneration is one of the early and crucial stages in AMD. It has been suggested that microglia and macrophages may be involved in the impairment of RPE, but how they and RPE are influenced by other factors present as AMD develops is unclear. Therefore the purpose of this study was to determine the role of macrophages in RPE degeneration in the presence of cytokines and oxidative stress likely to be present as AMD develops. METHODS: A co-culture model system was set up using bone marrow-derived macrophages and brain or retinal microglia cultured with RPE. Cytokines (IL-1ß, TNF-α, IFN-γ, and IL-6) and oxidized low-density lipoprotein were included in the culture at concentrations estimated to be likely during AMD, and apoptosis of RPE cells determined using flow cytometry to detect annexin V. RESULTS: Macrophages were shown capable of enhancing the apoptosis of RPE cells in a contact-dependent manner. IL-1ß, IFN-γ, IL-6, TNF-α, and oxLDL increased apoptosis; they increased RPE cell apoptosis directly, increased the susceptibility of RPE to subsequent apoptosis in the presence of microglia/macrophages, and increased the ability of microglia/macrophages to cause apoptosis. CONCLUSIONS: These findings indicate that microglia and macrophages are capable of enhancing the degeneration of RPE, which are crucial in AMD development. However this is dependent on the microenvironment present as AMD develops.

Macroautophagy in Endogenous Processing of Self- and Pathogen-Derived Antigens for MHC Class II Presentation.

Although autophagy is a process that has been studied for several years its link with antigen presentation and T cell immunity has only recently emerged. Autophagy, which means "self-eating," is important to maintain cell homeostasis and refers to a collection of mechanisms that delivers intracellular material for degradation into lysosomes. Among them, macroautophagy pathway has many implications in different biological processes, including innate and adaptive immunity. In particular, macroautophagy can provide a substantial source of intracellular antigens for loading onto MHC class II molecules using the alternative MHC class II pathway. Through autophagosomes, endogenous self-antigens as well as antigens derived from intracellular pathogens can be delivered to MHC class II compartment and presented to CD4(+) T cells. The pathway will, therefore, impact both peripheral T cell tolerance and the pathogen specific immune response. This review will describe the contribution of autophagy to intracellular presentation of endogenous self- or pathogen-derived antigens via MHC class II and its consequences on CD4(+) T cell responses.

S100B Up-Regulates Macrophage Production of IL1ß and CCL22 and Influences Severity of Retinal Inflammation.

S100B is a Ca2+ binding protein and is typically associated with brain and CNS disorders. However, the role of S100B in an inflammatory situation is not clear. The aim of the study was to determine whether S100B is likely to influence inflammation through its effect on macrophages. A murine macrophage cell line (RAW 264.7) and primary bone marrow derived macrophages were used for in vitro studies and a model of retinal inflammatory disease in which pathogenesis is highly dependent on macrophage infiltration, Experimental Autoimmune Uveoretinitis, for in vitro study. Experimental Autoimmune Uveoretinitis is a model for the human disease posterior endogenous uveoretinitis, a potentially blinding condition, with an autoimmune aetiology, that mainly affects the working age group. To date the involvement of S100B in autoimmune uveoretinitis has not been investigated. Real-time PCR array analysis on RAW 246.7 cells indicated up-regulation of gene expression for various cytokines/chemokines in response to S100B, IL-1ß and CCL22 in particular and this was confirmed by real-time PCR. In addition flow cytometry and ELISA confirmed up-regulation of protein production in response to S100B for pro-IL-1ß and CCL22 respectively. This was the case for both RAW 264.7 cells and bone marrow derived macrophages. Induction of EAU with retinal antigen in mice in which S100B had been deleted resulted in a significantly reduced level of disease compared to wild-type mice, as determined by topical endoscopic fundus imaging and histology grading. Macrophage infiltration was also significantly reduced in S100B deleted mice. Real-time PCR analysis indicated that this was associated with reduction in CCL22 and IL-1ß in retinas from S100B knock-out mice. In conclusion S100B augments the inflammatory response in uveoretinitis and this is likely to be, at least in part, via a direct effect on macrophages.

Pomalidomide is nonteratogenic in chicken and zebrafish embryos and nonneurotoxic in vitro.

Thalidomide and its analog, Lenalidomide, are in current use clinically for treatment of multiple myeloma, complications of leprosy and cancers. An additional analog, Pomalidomide, has recently been licensed for treatment of multiple myeloma, and is purported to be clinically more potent than either Thalidomide or Lenalidomide. Using a combination of zebrafish and chicken embryos together with in vitro assays we have determined the relative anti-inflammatory activity of each compound. We demonstrate that in vivo embryonic assays Pomalidomide is a significantly more potent anti-inflammatory agent than either Thalidomide or Lenalidomide. We tested the effect of Pomalidomide and Lenalidomide on angiogenesis, teratogenesis, and neurite outgrowth, known detrimental effects of Thalidomide. We found that Pomalidomide, displays a high degree of cell specificity, and has no detectable teratogenic, antiangiogenic or neurotoxic effects at potent anti-inflammatory concentrations. This is in marked contrast to Thalidomide and Lenalidomide, which had detrimental effects on blood vessels, nerves, and embryonic development at anti-inflammatory concentrations. This work has implications for Pomalidomide as a treatment for conditions Thalidomide and Lenalidomide treat currently.