Immunology: A helping hand against autoimmunity

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Retinoic acid-related Orphan Receptor γ (RORγ): connecting sterol metabolism to regulation of the immune system and autoimmune disease

Cholesterol and its metabolites are bioactive lipids that interact with and regulate the activity of various proteins and signaling pathways that are implicated in the control of a variety of physiological and pathological processes. Recent studies revealed that retinoic acid-related orphan receptors, RORα and γ, members of the ligand-dependent nuclear receptor superfamily, exhibit quite a wide binding specificity for a number of sterols. Several cholesterol intermediates and metabolites function as natural ligands of RORα and RORγ and act as agonists or inverse agonists. Changes in cholesterol homeostasis that alter the level or type of sterol metabolites in cells, can either enhance or inhibit ROR transcriptional activity that subsequently result in changes in the physiological processes regulated by RORs, including various immune responses and metabolic pathways. Consequently, this might negatively or positively impact pathologies, in which RORs are implicated, such as autoimmune disease, inflammation, metabolic syndrome, cancer, and several neurological disorders. Best studied are the links between cholesterol metabolism, RORγt activity, and their regulation of Th17 differentiation and autoimmune disease. The discovery that Th17-dependent inflammation is significantly attenuated in RORγ-deficient mice in several experimental autoimmune disease models, initiated a search for ROR modulators that led to the identification of a number of small molecular weight RORγ inverse agonists. The inverse agonists suppress Th17 differentiation and IL-17 production and protect against autoimmunity. Together, these studies suggest that RORγt may provide an attractive therapeutic target in the management of several (inflammatory) diseases.

Retinoic Acid-Related Orphan Receptors (RORs): Regulatory Functions in Immunity, Development, Circadian Rhythm, and Metabolism

In this overview, we provide an update on recent progress made in understanding the mechanisms of action, physiological functions, and roles in disease of retinoic acid related orphan receptors (RORs). We are particularly focusing on their roles in the regulation of adaptive and innate immunity, brain function, retinal development, cancer, glucose and lipid metabolism, circadian rhythm, metabolic and inflammatory diseases and neuropsychiatric disorders. We also summarize the current status of ROR agonists and inverse agonists, including their regulation of ROR activity and their therapeutic potential for management of various diseases in which RORs have been implicated.

Retinoic Acid-Related Orphan Receptors (RORs): Regulatory Functions in Immunity, Development, Circadian Rhythm, and Metabolism

In this overview, we provide an update on recent progress made in understanding the mechanisms of action, physiological functions, and roles in disease of retinoic acid related orphan receptors (RORs). We are particularly focusing on their roles in the regulation of adaptive and innate immunity, brain function, retinal development, cancer, glucose and lipid metabolism, circadian rhythm, metabolic and inflammatory diseases and neuropsychiatric disorders. We also summarize the current status of ROR agonists and inverse agonists, including their regulation of ROR activity and their therapeutic potential for management of various diseases in which RORs have been implicated.

RORγt-specific transcriptional interactomic inhibition suppresses autoimmunity associated with TH17 cells

The nuclear hormone receptor retinoic acid-related orphan receptor gamma t (RORγt) is a transcription factor (TF) specific to TH17 cells that produce interleukin (IL)-17 and have been implicated in a wide range of autoimmunity. Here, we developed a novel therapeutic strategy to modulate the functions of RORγt using cell-transducible form of transcription modulation domain of RORγt (tRORγt-TMD), which can be delivered effectively into the nucleus of cells and into the central nerve system (CNS). tRORγt-TMD specifically inhibited TH17-related cytokines induced by RORγt, thereby suppressing the differentiation of naïve T cells into TH17, but not into TH1, TH2, or Treg cells. tRORγt-TMD injected into experimental autoimmune encephalomyelitis (EAE) animal model can be delivered effectively in the splenic CD4(+) T cells and spinal cord-infiltrating CD4(+) T cells, and suppress the functions of TH17 cells. The clinical severity and incidence of EAE were ameliorated by tRORγt-TMD in preventive and therapeutic manner, and significant reduction of both infiltrating CD4(+) IL-17(+) T cells and inflammatory cells into the CNS was observed. As a result, the number of spinal cord demyelination was also reduced after tRORγt-TMD treatment. With the same proof of concept, tTbet-TMD specifically blocking TH1 differentiation improved the clinical incidence of rheumatoid arthritis (RA). Therefore, tRORγt-TMD and tTbet-TMD can be novel therapeutic reagents with the natural specificity for the treatment of inflammatory diseases associated with TH17 or TH1. This strategy can be applied to treat various diseases where a specific transcription factor has a key role in pathogenesis.

Therapeutic targeting of STAT pathways in CNS autoimmune diseases

Signal transducers and activators of transcription (STATs) transduce extracellular signals that regulate the initiation, duration and intensity of immune responses. However, unbridled activation of STATs by pro-inflammatory cytokines or growth factors contributes to pathogenic autoimmunity. In this review, we briefly discuss STAT pathways that promote the development and expansion of T cells that mediate two CNS inflammatory diseases, multiple sclerosis (MS) and uveitis. Particular focus is on animal models of MS and uveitis and new approaches to the treatment of CNS autoimmune diseases based on therapeutic targeting of Th17 cells and STAT pathways.

Prospero-related homeobox 1 (Prox1) functions as a novel modulator of retinoic acid-related orphan receptors α- and γ-mediated transactivation

In this study, we identify Prospero-related homeobox 1 (Prox1) as a novel co-repressor of the retinoic acid-related orphan receptors, RORα and RORγ. Prox1 interacts directly with RORγ and RORα and negatively regulates their transcriptional activity. The AF2 domain of RORs is essential for the interaction, whereas Prox1 interacts with RORs through either its 28 amino acids N-terminal region or its C-terminal prospero-like domain. RORγ antagonists stabilize the interaction between RORγ and Prox1. The homeodomain and the interaction through the prospero-like domain of Prox1 are critical for its repression of ROR transcriptional activity. Chromatin immunoprecipitation analysis demonstrated that in liver, Prox1 is recruited to the ROR response element sites of the clock genes, brain and muscle Arnt-like protein 1 (Bmal1), neuronal PAS domain protein 2 (Npas2) and cryptochrome 1 (Cry1), as part of the same complex as RORs. Knockdown of Prox1 by siRNAs in human hepatoma Huh-7 cells increased the expression of RORγ and several ROR-target genes, along with increased histone acetylation at these ROR response element sites. Chromatin immunoprecipitation sequencing analysis suggests that Prox1 is a potential ROR target gene in liver, which is supported by the regulation of the rhythmic expression of Prox1 by RORγ. Our data suggest that Prox1 is part of a feedback loop that negatively regulates the transcriptional control of clock and metabolic networks by RORs.

Retinoic acid-related orphan receptors α and γ: key regulators of lipid/glucose metabolism, inflammation, and insulin sensitivity

Retinoic acid-related orphan receptors RORα and RORγ play a regulatory role in lipid/glucose homeostasis and various immune functions, and have been implicated in metabolic syndrome and several inflammatory diseases. RORα-deficient mice are protected against age- and diet-induced obesity, hepatosteatosis, and insulin resistance. The resistance to hepatosteatosis in RORα-deficient mice is related to the reduced expression of several genes regulating lipid synthesis, transport, and storage. Adipose tissue-associated inflammation, which plays a critical role in the development of insulin resistance, is considerably diminished in RORα-deficient mice as indicated by the reduced infiltration of M1 macrophages and decreased expression of many proinflammatory genes. Deficiency in RORγ also protects against diet-induced insulin resistance by a mechanism that appears different from that in RORα deficiency. Recent studies indicated that RORs provide an important link between the circadian clock machinery and its regulation of metabolic genes and metabolic syndrome. As ligand-dependent transcription factors, RORs may provide novel therapeutic targets in the management of obesity and associated metabolic diseases, including hepatosteatosis, adipose tissue-associated inflammation, and insulin resistance.

Highlights of the advances in basic immunology in 2011

In this review, we summarize the major fundamental advances in immunological research reported in 2011. The highlights focus on the improved understanding of key questions in basic immunology, including the initiation and activation of innate responses as well as mechanisms for the development and function of various T-cell subsets. The research includes the identification of novel cytosolic RNA and DNA sensors as well as the identification of the novel regulators of the Toll-like receptor (TLR) and retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling pathway. Moreover, remarkable advances have been made in the developmental and functional properties of innate lymphoid cells (ILCs). Helper T cells and regulatory T (Treg) cells play indispensable roles in orchestrating adaptive immunity. There have been exciting discoveries regarding the regulatory mechanisms of the development of distinct T-cell subsets, particularly Th17 cells and Treg cells. The emerging roles of microRNAs (miRNAs) in T cell immunity are discussed, as is the recent identification of a novel T-cell subset referred to as follicular regulatory T (TFR) cells.

Therapeutic targeting of STAT3 (signal transducers and activators of transcription 3) pathway inhibits experimental autoimmune uveitis

Mice with targeted deletion of STAT3 in CD4⁺ T-cells do not develop experimental autoimmune uveitis (EAU) or experimental autoimmune encephalomyelitis (EAE), in part, because they cannot generate pathogenic Th17 cells. In this study, we have used ORLL-NIH001, a small synthetic compound that inhibits transcriptional activity of STAT3, to ameliorate EAU, an animal model of human posterior uveitis. We show that by attenuating inflammatory properties of uveitogenic lymphocytes, ORLL-NIH001 inhibited the recruitment of inflammatory cells into the retina during EAU and prevented the massive destruction of the neuroretina caused by pro-inflammatory cytokines produced by the autoreactive lymphocytes. Decrease in disease severity observed in ORLL-NIH001-treated mice, correlated with the down-regulation of α4β1 and α4β7 integrin activation and marked reduction of CCR6 and CXCR3 expression, providing a mechanism by which ORLL-NIH001 mitigated EAU. Furthermore, we show that ORLL-NIH001 inhibited the expansion of human Th17 cells, underscoring its potential as a drug for the treatment of human uveitis. Two synthetic molecules that target the Th17 lineage transcription factors, RORγt and RORα, have recently been suggested as potential drugs for inhibiting Th17 development and treating CNS inflammatory diseases. However, inhibiting STAT3 pathways completely blocks Th17 development, as well as, prevents trafficking of inflammatory cells into CNS tissues, making STAT3 a more attractive therapeutic target. Thus, use of ORLL-NIH001 to target the STAT3 transcription factor, thereby antagonizing Th17 expansion and expression of proteins that mediate T cell chemotaxis, provides an attractive new therapeutic approach for treatment of posterior uveitis and other CNS autoimmune diseases mediated by Th17 cells.