Inhibition of stearoyl-CoA desaturase 1 (SCD1) enhances the antitumor T cell response through regulating ß-catenin signaling in cancer cells and ER stress in T cells and synergizes with anti-PD-1 antibody.

BACKGROUND: Understanding the mechanisms of non-T cell inflamed tumor microenvironment (TME) and their modulation are important to improve cancer immunotherapies such as immune checkpoint inhibitors. The involvement of various immunometabolisms has recently been indicated in the formation of immunosuppressive TME. In this study, we investigated the immunological roles of stearoyl-CoA desaturase 1 (SCD1), which is essential for fatty acid metabolism, in the cancer immune response. METHODS: We investigated the roles of SCD1 by inhibition with the chemical inhibitor or genetic manipulation in antitumor T cell responses and the therapeutic effect of anti-programmed cell death protein 1 (anti-PD-1) antibody using various mouse tumor models, and their cellular and molecular mechanisms. The roles of SCD1 in human cancers were also investigated by gene expression analyses of colon cancer tissues and by evaluating the related free fatty acids in sera obtained from patients with non-small cell lung cancer who were treated with anti-PD-1 antibody. RESULTS: Systemic administration of a SCD1 inhibitor in mouse tumor models enhanced production of CCL4 by cancer cells through reduction of Wnt/ß-catenin signaling and by CD8+ effector T cells through reduction of endoplasmic reticulum stress. It in turn promoted recruitment of dendritic cells (DCs) into the tumors and enhanced the subsequent induction and tumor accumulation of antitumor CD8+ T cells. SCD1 inhibitor was also found to directly stimulate DCs and CD8+ T cells. Administration of SCD1 inhibitor or SCD1 knockout in mice synergized with an anti-PD-1 antibody for its antitumor effects in mouse tumor models. High SCD1 expression was observed in one of the non-T cell-inflamed subtypes in human colon cancer, and serum SCD1 related fatty acids were correlated with response rates and prognosis of patients with non-small lung cancer following anti-PD-1 antibody treatment. CONCLUSIONS: SCD1 expressed in cancer cells and immune cells causes immunoresistant conditions, and its inhibition augments antitumor T cells and therapeutic effects of anti-PD-1 antibody. Therefore, SCD1 is an attractive target for the development of new diagnostic and therapeutic strategies to improve current cancer immunotherapies including immune checkpoint inhibitors.

Inhibition of stearoyl-CoA desaturases suppresses follicular help T- and germinal center B- cell responses.

Stearoyl-CoA desaturases (SCD) are endoplasmic reticulum (ER)-associated enzymes that catalyze the synthesis of the monounsaturated fatty acids (MUFAs). As such, SCD play important roles in maintaining the intracellular balance between saturated fatty acid (SFAs) and MUFAs. The roles of SCD in CD4+ T-helper cell responses are currently unexplored. Here, we have found that murine and human follicular helper T (TFH ) cells express higher levels of SCD compared to non-TFH cells. Further, the expression of SCD in TFH cells is dependent on the TFH lineage-specification transcription factor BCL6. We found that the inhibition of SCD impaired TFH cell maintenance and shifted the balance between TFH and follicular regulatory T (TFR ) cells in the spleen. Consequently, SCD inhibition dampened germinal center B-cell responses following influenza immunization. Mechanistically, we found that SCD inhibition led to increased ER stress and enhanced TFH cell apoptosis in vitro and in vivo. These results reveal a possible link between fatty acid metabolism and cellular and humoral responses induced by immunization or potentially, autoimmunity.

Identification and characterization of stearoyl-CoA desaturase in Toxoplasma gondii.

Few information of the function of stearoyl-coenzyme A (CoA) desaturase (SCD) in apicomplaxan parasite has been obtained. In this study, we retrieved a putative fatty acyl-CoA desaturase (TGGT1_238950) by a protein alignment with Plasmodium falciparum SCD in ToxoDB. A typical Δ9-desaturase domain was revealed in this protein. The putative desaturase was tagged with HA endogenously in Toxoplasma gondii, and the endoplasmic reticulum localization of the putative desaturase was revealed, which was consistent with the fatty acid desaturases in other organisms. Therefore, the TGGT1_238950 was designated T. gondii SCD. Based on CRISPR/Cas9 gene editing technology, SCD conditional knockout mutants in the T. gondii TATi strain were obtained. The growth in vitro and pathogenicity in mice of the mutants suggested that SCD might be dispensable for tachyzoite growth and proliferation. The SCD-overexpressing line was constructed to further explore SCD function. The portion of palmitoleic acid and oleic acid were increased in SCD-overexpressing parasites, compared with the RH parental strain, indicating that T. gondii indeed is competent for unsaturated fatty acid synthesis. The SCD-overexpressing tachyzoites propagated slower than the parental strain, with a decreased invasion capability and weaker pathogenicity in mice. The TgIF2α phosphorylation and the expression changes of several genes demonstrated that ER stress was triggered in the SCD-overexpressing parasites, which were more apt toward autophagy and apoptosis. The function of unsaturated fatty acid synthesis of TgSCD was consistent with our hypothesis. On the other hand, SCD might also be involved in tachyzoite autophagy and apoptosis.

Loss of Stearoyl-CoA desaturase-1 attenuates adipocyte inflammation: effects of adipocyte-derived oleate.

BACKGROUND AND PURPOSE: Adipose inflammation is crucial to the pathogenesis of metabolic disorders. This study aimed at identify the effects of stearoyl-CoA desaturase-1 (SCD1) on the inflammatory response of a paracrine network involving adipocytes, macrophages, and endothelial cells. METHODS AND RESULTS: Loss of SCD1 in both genetic (Agouti) and diet-induced obesity (high-fat diet) mouse models prevented inflammation in white adipose tissue and improved its basal insulin signaling. In SCD1-deficient mice, white adipose tissue exhibited lower inflammation, with a reduced response to lipopolysaccharide in isolated adipocytes, but not in peritoneal macrophages. Mimicking the in vivo paracrine regulation of white adipose tissue inflammation, SCD1-deficient adipocyte-conditioned medium attenuated the induction of tumor necrosis factor (TNF) alpha/interleukin 1beta gene expression in RAW264.7 macrophages and reduced the adhesion response in endothelial cells. We further demonstrated that the adipocyte-derived oleate (18:1n9), but not palmitoleate (16:1n7), mediated the inflammation in macrophages and adhesion responses in endothelial cells. CONCLUSIONS: Loss of SCD1 attenuates adipocyte inflammation and its paracrine regulation of inflammation in macrophages and endothelial cells. The reduced oleate level is linked to the inflammation-modulating effects of SCD1 deficiency.

Altered expression of lipid metabolism and immune response genes in the frontal cortex of suicide completers.

BACKGROUND: Studies investigating the association between low cholesterol and suicidality have generated a range of ideas about how cholesterol might play a role in influencing suicide risk, extending studies to other aspects of lipid metabolism, as well as immune response, in relation to suicide. METHODS: We performed large-scale microarray gene expression analysis using the Affymetrix HG-U133 chipset and focused our investigation on the expression profile of genes related to lipid metabolism and immune response in post-mortem brains from suicide completers and comparison subjects. We used tissue from three regions of the frontal cortex (Brodmann areas (BA) 8/9, 11, and 47) from 22 male suicide completers, 15 of whom were diagnosed with major depressive disorder, and 13 male comparison subjects. RESULTS: Fatty acid desaturase (FADS1), leptin receptor (LEPR), phosphoinositide-3-kinase (class 2 alpha; PIK3C2A) and stearoyl-CoA desaturase (SCD) were consistently down-regulated in all three regions of the frontal cortex of depressed suicides compared to comparison subjects, and were among the genes for which significant correlations were observed between our microarray and real-time PCR data. LIMITATIONS: Given the absence of a non-suicidal depressed comparison group in this study, it cannot be ascertained whether the gene expression changes identified are associated with depression or suicide. CONCLUSIONS: Our findings suggest a role for lipid metabolism and immune response genes in depressed suicide completers and lend further support to the relationship between lipid metabolism and suicidality.

Involvement of stearoyl-CoA desaturase in the reduction of amidoxime prodrugs.

1. This study investigates the enzymatic reduction of N-hydroxylated amidines by porcine adipose tissue and the possible involvement of stearoyl-CoA desaturase (SCD). 2. The reduction of the model substrate benzamidoxime was studied with porcine adipose tissue microsomes and partially purified SCD from SCD-enriched rat liver microsomes. 3. Inhibitor studies with these microsomal preparations using various inhibitors including anti-SCD antibody, cyanide and stearoyl-CoA supported a role for SCD in the reduction of N-hydroxylated amidines in adipose tissue. The content and activity of SCD in these microsomes was established by Western blot and SCD activity determinations. Additionally, a reconstituted system of cytochrome b(5), NADH-cytochrome b(5) reductase and partially purified SCD from SCD-enriched rat liver microsomes supported benzamidoxime reductase activity that was inhibitable by an anti-SCD antibody. 4. The results support the participation of SCD in the reduction of amidoxime prodrugs and demonstrate for the first time that SCD can also accept foreign compounds (xenobiotics) as substrates.

Preparation of antiserum against rat delta6-desaturase and its use to evaluate the desaturase protein levels in rats treated with gemfibrozil, a ligand for peroxisome proliferator-activated receptor alpha.

Anti-rat delta6-desaturase serum was produced by immunizing rabbits with the 14 N-terminal amino acids (2-15) of rat delta6-desaturase. The antiserum prevented the enzymatic activity of delta6-desaturase in microsomes. Subsequently, the antiserum was used to demonstrate that gemfibrozil, a ligand for peroxisome proliferator-activated receptor alpha, is involved in activating delta6-desaturase gene expression, thereby elevating the protein level and the activity.