Abstract 2121: Gene expression and functional characterization of obesity-induced MDSC to uncover the link between obesity and cancer risk

Strong epidemiologic evidence suggests that excess body weight gain is a major risk of at least 13 different types of cancers. One of the mechanisms explaining the increased cancer incidence in obese patients is associated with the chronic low-grade inflammatory condition. Myeloid cells including macrophages and Myeloid-derived suppressor cells (MDSC) are increased in advanced adiposity. Previous studies in mouse models have shown that obesity-induced MDSC play a protective role on metabolic control; however, in the presence of malignant cells, MDSC facilitates tumor growth and metastasis. Our data show that compared to non-obese individuals, patients with severe obesity (body mass index [BMI] > 40) have a significant increase of circulating granulocytic cells displaying a gene signature resembling tumor-MDSC. Intriguingly, obesity-induced MDSC lacked the potent immunosuppressive function; and therefore, we called them obesity-induced G-MDSC-like cells (Ob-MDSC). The mechanisms underlying the regulation of MDSC phenotype in obesity and obesity-related cancer are unclear. We found that LDL, one altered obesity-related factor, and LPS differentially impact the expression of several genes including the immunosuppressive MDSC markers, arginase-1 and iNOS, when comparing mouse bone marrow-derived MDSC from high-fat fed mice with low-fat fed mice. This finding indicates that the responsiveness of MDSC may be regulated by their long-lasting exposure to the obese microenvironment. Therefore, we propose that long-term adaptation of MDSC is induced by dysfunctional metabolic factors in obesity that modulate their response to subsequent triggers, such as signals derived by the tumor microenvironment (TMA) in the context of obesity-associated cancer. Our data from obese mice with Diethylnitrosamine (DEN)-induced hepatocellular carcinoma and genetically altered hepatic lipid and lipoprotein metabolism show an increased infiltration of G-MDSC associated with enhanced tissue chemokine signaling pathway, ECM remodeling/metastasis, inflammation, and epigenetic and transcriptional regulation. Together our data suggest that chronic exposure to an obesity-related environment establishes a phenotype prone to become pro-tumor MDSC. The identification of key regulators of the gene expression driving the immunosuppressive phenotype of MDSC in obesity is critical for the discovery of therapeutical targets to reduce the risk of obesity-associated cancers.

Citation Format: Maria D. Sanchez-Pino, Ramesh Thylur Puttalingaiah, Jone Garai, Jovanny Zabaleta, Randall L. Mynatt, William Richardson, Augusto Ochoa. Gene expression and functional characterization of obesity-induced MDSC to uncover the link between obesity and cancer risk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2121.

Herpes Simplex Virus-1 Induced Serotonin-Associated Metabolic Pathways Correlate With Severity of Virus- and Inflammation-Associated Ocular Disease

Herpes simplex virus-associated diseases are a complex interaction between cytolytic viral replication and inflammation. Within the normally avascular and immunoprivileged cornea, HSV ocular infection can result in vision-threatening immune-mediated herpetic keratitis, the leading infectious cause of corneal blindness in the industrialized world. Viral replicative processes are entirely dependent upon numerous cellular biosynthetic and metabolic pathways. Consistent with this premise, HSV infection was shown to profoundly alter gene expression associated with cellular amino acid biosynthetic pathways, including key tryptophan metabolism genes. The essential amino acid tryptophan is crucial for pathogen replication, the generation of host immune responses, and the synthesis of neurotransmitters, such as serotonin. Intriguingly, Tryptophan hydroxylase 2 (TPH2), the neuronal specific rate-limiting enzyme for serotonin synthesis, was the most significantly upregulated gene by HSV in an amino acid metabolism PCR array. Despite the well-defined effects of serotonin in the nervous system, the association of peripheral serotonin in disease-promoting inflammation has only recently begun to be elucidated. Likewise, the impact of serotonin on viral replication and ocular disease is also largely unknown. We therefore examined the effect of HSV-induced serotonin-associated synthesis and transport pathways on HSV-1 replication, as well as the correlation between HSV-induced ocular serotonin levels and disease severity. HSV infection induced expression of the critical serotonin synthesis enzymes TPH-1, TPH-2, and DOPA decarboxylase (DDC), as well as the serotonin transporter, SERT. Concordantly, HSV-infected cells upregulated serotonin synthesis and its intracellular uptake. Increased serotonin synthesis and uptake was shown to influence HSV replication. Exogenous addition of serotonin increased HSV-1 yield, while both TPH-1/2 and SERT pharmacological inhibition reduced viral yield. Congruent with these in vitro findings, rabbits intraocularly infected with HSV-1 exhibited significantly higher aqueous humor serotonin concentrations that positively and strongly correlated with viral load and ocular disease severity. Collectively, our findings indicate that HSV-1 promotes serotonin synthesis and cellular uptake to facilitate viral replication and consequently, serotonin's proinflammatory effects may enhance the development of ocular disease.

Changes in Chronic Inflammatory Cells by Bariatric Weight Loss Surgery

Obesity is characterized by chronic low grade systemic inflammation, where myeloid cells play a critical role. Myeloid-derived suppressor cells (MDSC; Monocytic [M-MDSC] and Granulocytic [PMN-MDSC] subsets) have been identified in cancer and other chronic inflammatory diseases. A few studies have shown a significant accumulation of MDSC in blood and different tissues in diet-induced obese mice and we also observed a significant accumulation of MDSC in mice made obese by a high fat-high sucrose diet compared with lean animals. The mechanisms linking obesity and MDSC activation or the effects of weight loss are unknown. We have compared the frequency of MDSC in blood and omental adipose tissue in obese patients (BMI≥40) with non-obese controls (BMI≤25), and evaluated the effect of bariatric surgery over time (3, 6 and 12 months). Our preliminary data shows that PMN-MDSC are significantly increased in patients prior to surgery, but drastically decrease 3 months after bariatric surgery, associated with improvement of obesity-related metabolic dysfunction. These data support the hypothesis that increased caloric intake and obesity stimulate the induction of MDSC, which promote a chronic inflammatory environment, while weight loss intervention reduces MDSC, eliminating the inflammation and controlling the metabolic dysfunction condition. Furthermore, our in vitro studies demonstrated that the uptake of lipoproteins transforms normal myeloid cells into highly immunosuppressive MDSC by inducing the expression of Arginase I. Thus understanding the cellular and molecular mechanisms by which obesity leads to the induction of MDSC is essential to understand the role of those MDSC in the obesity-related pathologies.

Fuelling the mechanisms of asthma: Increased fatty acid oxidation in inflammatory immune cells may represent a novel therapeutic target

BACKGROUND

Increasing evidence has shown the close link between energy metabolism and the differentiation, function, and longevity of immune cells. Chronic inflammatory conditions such as parasitic infections and cancer trigger a metabolic reprogramming from the preferential use of glucose to the up-regulation of fatty acid oxidation (FAO) in myeloid cells, including macrophages and granulocytic and monocytic myeloid-derived suppressor cells. Asthma is a chronic inflammatory condition where macrophages, eosinophils, and polymorphonuclear cells play an important role in its pathophysiology.

OBJECTIVE

We tested whether FAO might play a role in the development of asthma-like traits and whether the inhibition of this metabolic pathway could represent a novel therapeutic approach.

METHODS

OVA- and house dust mite (HDM)-induced murine asthma models were used in this study.

RESULTS

Key FAO enzymes were significantly increased in the bronchial epithelium and inflammatory immune cells infiltrating the respiratory epithelium of mice exposed to OVA or HDM. Pharmacologic inhibition of FAO significantly decreased allergen-induced airway hyperresponsiveness, decreased the number of inflammatory cells, and reduced the production of cytokines and chemokines associated with asthma.

CONCLUSIONS AND CLINICAL RELEVANCE

These novel observations suggest that allergic airway inflammation increases FAO in inflammatory cells to support the production of cytokines, chemokines, and other factors important in the development of asthma. Inhibition of FAO by re-purposing existing drugs approved for the treatment of heart disease may provide a novel therapeutic approach for the treatment of asthma.