Modulation of PKM activity affects the differentiation of TH17 cells

Small molecules that promote the metabolic activity of the pyruvate kinase isoform PKM2, such as TEPP-46 and DASA-58, limit tumorigenesis and inflammation. To understand how these compounds alter T cell function, we assessed their therapeutic activity in a mouse model of T cell-mediated autoimmunity that mimics multiple sclerosis (MS). TH17 cells are believed to orchestrate MS pathology, in part, through the production of two proinflammatory cytokines: interleukin-17 (IL-17) and GM-CSF. We found that both TEPP-46 and DASA-58 suppressed the development of IL-17-producing TH17 cells but increased the generation of those producing GM-CSF. This switch redirected disease pathology from the spinal cord to the brain. In addition, we found that activation of PKM2 interfered with TGF-β1 signaling, which is necessary for the development of TH17 and regulatory T cells. Collectively, our data clarify the therapeutic potential of PKM2 activators in MS-like disease and how these agents alter T cell function.

The active contribution of OPCs to neuroinflammation is mediated by LRP1

Oligodendrocyte progenitor cells (OPCs) account for about 5% of total brain and spinal cord cells, giving rise to myelinating oligodendrocytes that provide electrical insulation to neurons of the CNS. OPCs have also recently been shown to regulate inflammatory responses and glial scar formation, suggesting functions that extend beyond myelination. Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifaceted phagocytic receptor that is highly expressed in several CNS cell types, including OPCs. Here, we have generated an oligodendroglia-specific knockout of LRP1, which presents with normal myelin development, but is associated with better outcomes in two animal models of demyelination (EAE and cuprizone). At a mechanistic level, LRP1 did not directly affect OPC differentiation into mature oligodendrocytes. Instead, animals lacking LRP1 in OPCs in the demyelinating CNS were characterized by a robust dampening of inflammation. In particular, LRP1-deficient OPCs presented with impaired antigen cross-presentation machinery, suggesting a failure to propagate the inflammatory response and thus promoting faster myelin repair and neuroprotection. Our study places OPCs as major regulators of neuroinflammation in an LRP1-dependent fashion.

Modulation of the sigma-1 receptor-IRE1 pathway is beneficial in preclinical models of inflammation and sepsis

Sepsis is an often deadly complication of infection in which systemic inflammation damages the vasculature, leading to tissue hypoperfusion and multiple organ failure. Currently, the standard of care for sepsis is predominantly supportive, with few therapeutic options available. Because of increased sepsis incidence worldwide, there is an urgent need for discovery of novel therapeutic targets and development of new treatments. The recently discovered function of the endoplasmic reticulum (ER) in regulation of inflammation offers a potential avenue for sepsis control. Here, we identify the ER-resident protein sigma-1 receptor (S1R) as an essential inhibitor of cytokine production in a preclinical model of septic shock. Mice lacking S1R succumb quickly to hypercytokinemia induced by a sublethal challenge in two models of acute inflammation. Mechanistically, we find that S1R restricts the endonuclease activity of the ER stress sensor IRE1 and cytokine expression but does not inhibit the classical inflammatory signaling pathways. These findings could have substantial clinical implications, as we further find that fluvoxamine, an antidepressant therapeutic with high affinity for S1R, protects mice from lethal septic shock and dampens the inflammatory response in human blood leukocytes. Our data reveal the contribution of S1R to the restraint of the inflammatory response and place S1R as a possible therapeutic target to treat bacterial-derived inflammatory pathology.

Exploring Non-Metabolic Functions of Glycolytic Enzymes in Immunity

At the beginning of the twentieth century, discoveries in cancer research began to elucidate the idiosyncratic metabolic proclivities of tumor cells (1). Investigators postulated that revealing the distinct nutritional requirements of cells with unchecked growth potential would reveal targetable metabolic vulnerabilities by which their survival could be selectively curtailed. Soon thereafter, researchers in the field of immunology began drawing parallels between the metabolic characteristics of highly proliferative cancer cells and those of immune cells that respond to perceived threats to host physiology by invading tissues, clonally expanding, and generating vast amounts of pro-inflammatory effector molecules to provide the host with protection. Throughout the past decade, increasing effort has gone into elucidating the biosynthetic and bioenergetic requirements of immune cells during inflammatory responses. It is now well established that, like tumor cells, immune cells must undergo metabolic adaptations to fulfill their effector functions (2, 3). Unraveling the metabolic adaptations that license inflammatory immune responses may lead to the development of novel classes of therapeutics for pathologies with prominent inflammatory components (e.g., autoimmunity). However, the translational potential of discoveries made toward this end is currently limited by the ubiquitous nature of the "pathologic" process being targeted: metabolism. Recent works have started to unravel unexpected non-metabolic functions for metabolic enzymes in the context of inflammation, including signaling and gene regulation. One way information gained through the study of immunometabolism may be leveraged for therapeutic benefit is by exploiting these non-canonical features of metabolic machinery, modulating their contribution to the immune response without impacting their basal metabolic functions. The focus of this review is to discuss the metabolically independent functions of glycolytic enzymes and how these could impact T cells, agents of the immune system that are commonly considered as orchestrators of auto-inflammatory processes.

Lineage-Specific Metabolic Properties and Vulnerabilities of T Cells in the Demyelinating Central Nervous System

Multiple sclerosis (MS) is a disease that is characterized by immune-mediated destruction of CNS myelin. Current MS therapies aim to block peripheral immune cells from entering the CNS. Although these treatments limit new inflammatory activity in the CNS, no treatment effectively prevents long-term disease progression and disability accumulation in MS patients. One explanation for this paradox is that current therapies are ineffective at targeting immune responses already present in the CNS. To this end, we sought to understand the metabolic properties of T cells that mediate ongoing inflammation in the demyelinating CNS. Using experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice, a well-studied model of MS, we showed that the CD4⁺ and CD8⁺ T cells that invade the EAE CNS are highly glycolytic. Elevated glycolytic rates in T cells isolated from the EAE CNS correlate with upregulated expression of glycolytic machinery and is essential for inflammatory responses to myelin. Surprisingly, we found that an inhibitor of GAPDH, 3-bromopyruvic acid (3-BrPa), blocks IFN-γ, but not IL-17A, production in immune cells isolated from the EAE CNS. Indeed, in vitro studies confirmed that the production of IFN-γ by differentiated Th1 cells is more sensitive to 3-BrPa than is the production of IL-17A by Th17 cells. Finally, in transfer models of EAE, 3-BrPa robustly attenuates the encephalitogenic potential of EAE-driving immune cells. To our knowledge, these data are among the first to demonstrate the metabolic properties of T cells in the demyelinating CNS in vivo.

LRP1 expression in microglia is protective during CNS autoimmunity

Multiple sclerosis is a devastating neurological disorder characterized by the autoimmune destruction of the central nervous system myelin. While T cells are known orchestrators of the immune response leading to MS pathology, the precise contribution of CNS resident and peripheral infiltrating myeloid cells is less well described. Here, we explore the myeloid cell function of Low-density lipoprotein receptor-related protein-1 (LRP1), a scavenger receptor involved in myelin clearance and the inflammatory response, in the context of Multiple sclerosis. Supporting its central role in Multiple sclerosis pathology, we find that LRP1 expression is increased in Multiple sclerosis lesions in comparison to the surrounding healthy tissue. Using two genetic mouse models, we show that deletion of LRP1 in microglia, but not in peripheral macrophages, negatively impacts the progression of experimental autoimmune encephalomyelitis, an animal model of Multiple sclerosis. We further show that the increased disease severity in experimental autoimmune encephalomyelitis is not due to haplodeficiency of the Cx3cr1 locus. At the cellular level, microglia lacking LRP1 adopt a pro-inflammatory phenotype characterized by amoeboid morphology and increased production of the inflammatory mediator TNF-α. We also show that LRP1 functions as a robust inhibitor of NF-kB activation in myeloid cells via a MyD88 dependent pathway, potentially explaining the increase in disease severity observed in mice lacking LRP1 expression in microglia. Taken together, our data suggest that the function of LRP1 in microglia is to keep these cells in an anti-inflammatory and neuroprotective status during inflammatory insult, including experimental autoimmune encephalomyelitis and potentially in Multiple sclerosis.