Thaddeus Carlson

Pro-inflammatory human Th17 cells selectively express P-glycoprotein and are refractory to glucocorticoids

Inflammatory T helper 17 cells in humans are distinguished by selective expression of MDR1 and are enriched in the gut of patients with Crohn’s disease.

Pharmacologic Inhibition of RORγt Regulates Th17 Signature Gene Expression and Suppresses Cutaneous Inflammation In Vivo

IL-17–producing CD4+Th17 cells, CD8+Tc17 cells, and γδ T cells play critical roles in the pathogenesis of autoimmune psoriasis. RORγt is required for the differentiation of Th17 cells and expression of IL-17. In this article, we describe a novel, potent, and selective RORγt inverse agonist (TMP778), and its inactive diastereomer (TMP776). This chemistry, for the first time to our knowledge, provides a unique and powerful set of tools to probe RORγt-dependent functions. TMP778, but not TMP776, blocked human Th17 and Tc17 cell differentiation and also acutely modulated IL-17A production and inflammatory Th17-signature gene expression (Il17a, Il17f, Il22, Il26, Ccr6, and Il23) in mature human Th17 effector/memory T cells. In addition, TMP778, but not TMP776, inhibited IL-17A production in both human and mouse γδ T cells. IL-23–induced IL-17A production was also blocked by TMP778 treatment. In vivo targeting of RORγt in mice via TMP778 administration reduced imiquimod-induced psoriasis-like cutaneous inflammation. Further, TMP778 selectively regulated Th17-signature gene expression in mononuclear cells isolated from both the blood and affected skin of psoriasis patients. In summary, to our knowledge, we are the first to demonstrate that RORγt inverse agonists: 1) inhibit Tc17 cell differentiation, as well as IL-17 production by γδ T cells and CD8+ Tc17 cells; 2) block imiquimod-induced cutaneous inflammation; 3) inhibit Th17 signature gene expression by cells isolated from psoriatic patient samples; and 4) block IL-23–induced IL-17A expression. Thus, RORγt is a tractable drug target for the treatment of cutaneous inflammatory disorders, which may afford additional therapeutic benefit over existing modalities that target only IL-17A.

Cytokine signals through PI-3 kinase pathway modulate Th17 cytokine production by CCR6+ human memory T cells

PI-3K–mediated repression of FOXO1 and KLF2 promotes proinflammatory cytokine expression by lineage-committed human CCR6+ Th17/Th22 memory cells.

TRIL, a functional component of the TLR4 signaling complex, highly expressed in brain

TLR4 is the primary sensor of LPS. In this study, we describe for the first time TLR4 interactor with leucine-rich repeats (TRIL), which is a novel component of the TLR4 complex. TRIL is expressed in a number of tissues, most prominently in the brain but also in the spinal cord, lung, kidney, and ovary. TRIL is composed of a signal sequence, 13 leucine-rich repeats, a fibronectin domain, and a single transmembrane spanning region. TRIL is induced by LPS in the human astrocytoma cell line U373, in murine brain following i.p. injection, and in human PBMC. Endogenous TRIL interacts with TLR4 and this interaction is greatly enhanced following LPS stimulation. TRIL also interacts with the TLR4 ligand LPS. Furthermore, U373 cells stably overexpressing TRIL display enhanced cytokine production in response to LPS. Finally, knockdown of TRIL using small interfering RNA attenuates LPS signaling and cytokine production in cell lines, human PBMC, and primary murine mixed glial cells. These results demonstrate that TRIL is a novel component of the TLR4 complex which may have particular relevance for the functional role of TLR4 in the brain.

Mice lacking Tbk1 activity exhibit immune cell infiltrates in multiple tissues and increased susceptibility to LPS-induced lethality

TBK1 is critical for immunity against microbial pathogens that activate TLR4‐ and TLR3‐dependent signaling pathways. To address the role of TBK1 in inflammation, mice were generated that harbor two copies of a mutant Tbk1 allele. This Tbk1Δ allele encodes a truncated Tbk1Δ protein that is catalytically inactive and expressed at very low levels. Upon LPS stimulation, macrophages from Tbk1Δ/Δ mice produce normal levels of proinflammatory cytokines (e.g., TNF‐α), but IFN‐β and RANTES expression and IRF3 DNA‐binding activity are ablated. Three‐month‐old Tbk1Δ/Δ mice exhibit mononuclear and granulomatous cell infiltrates in multiple organs and inflammatory cell infiltrates in their skin, and they harbor a 2‐fold greater amount of circulating monocytes than their Tbk1+/+ and Tbk1+/Δ littermates. Skin from 2‐week‐old Tbk1Δ/Δ mice is characterized by reactive changes, including hyperkeratosis, hyperplasia, necrosis, inflammatory cell infiltrates, and edema. In response to LPS challenge, 3‐month‐old Tbk1Δ/Δ mice die more quickly and in greater numbers than their Tbk1+/+ and Tbk1+/Δ counterparts. This lethality is accompanied by an overproduction of several proinflammatory cytokines in the serum of Tbk1Δ/Δ mice, including TNF‐α, GM‐CSF, IL‐6, and KC. This overproduction of serum cytokines in Tbk1Δ/Δ mice following LPS challenge and their increased susceptibility to LPS‐induced lethality may result from the reactions of their larger circulating monocyte compartment and their greater numbers of extravasated immune cells.

Halofuginone-induced amino acid starvation regulates Stat3-dependent Th17 effector function and reduces established autoimmune inflammation.

The IL-23 pathway is genetically linked to autoimmune disease in humans and is required for pathogenic Th17 cell function in mice. However, because IL-23R–expressing mature Th17 cells are rare and poorly defined in mice at steady-state, little is known about IL-23 signaling. In this study, we show that the endogenous CCR6+ memory T cell compartment present in peripheral lymphoid organs of unmanipulated mice expresses Il23r ex vivo, displays marked proinflammatory responses to IL-23 stimulation in vitro, and is capable of transferring experimental autoimmune encephalomyelitis. The prolyl-tRNA synthetase inhibitor halofuginone blocks IL-23–induced Stat3 phosphorylation and IL-23–dependent proinflammatory cytokine expression in endogenous CCR6+ Th17 cells via activation of the amino acid starvation response (AAR) pathway. In vivo, halofuginone shows therapeutic efficacy in experimental autoimmune encephalomyelitis, reducing both established disease progression and local Th17 cell effector function within the CNS. Mechanistically, AAR activation impairs Stat3 responses downstream of multiple cytokine receptors via selective, posttranscriptional suppression of Stat3 protein levels. Thus, our study reveals latent pathogenic functions of endogenous Th17 cells that are regulated by both IL-23 and AAR pathways and identifies a novel regulatory pathway targeting Stat3 that may underlie selective immune regulation by the AAR.

In vivo regulation of gene expression and T helper type 17 differentiation by RORγt inverse agonists.

The orphan nuclear receptor, retinoic acid receptor‐related orphan nuclear receptor γt (RORγt), is required for the development and pathogenic function of interleukin‐17A‐secreting CD4+ T helper type 17 (Th17) cells. Whereas small molecule RORγt antagonists impair Th17 cell development and attenuate autoimmune inflammation in vivo, the broader effects of these inhibitors on RORγt‐dependent gene expression in vivo has yet to be characterized. We show that the RORγt inverse agonist TMP778 acts potently and selectively to block mouse Th17 cell differentiation in vitro and to impair Th17 cell development in vivo upon immunization with the myelin antigen MOG35–55 plus complete Freunds adjuvant. Importantly, we show that TMP778 acts in vivo to repress the expression of more than 150 genes, most of which fall outside the canonical Th17 transcriptional signature and are linked to a variety of inflammatory pathologies in humans. Interestingly, more than 30 genes are related with SMAD3, a transcription factor involved in the Th17 cell differentiation. These results reveal novel disease‐associated genes regulated by RORγt during inflammation in vivo, and provide an early read on potential disease indications and safety concerns associated with pharmacological targeting of RORγt.

TRIL Is Involved in Cytokine Production in the Brain following Escherichia coli Infection

TLR4 interactor with leucine-rich repeats (TRIL) is a brain-enriched accessory protein that is important in TLR3 and TLR4 signaling. In this study, we generated Tril−/− mice and examined TLR responses in vitro and in vivo. We found a role for TRIL in both TLR4 and TLR3 signaling in mixed glial cells, consistent with the high level of expression of TRIL in these cells. We also found that TRIL is a modulator of the innate immune response to LPS challenge and Escherichia coli infection in vivo. Tril−/− mice produce lower levels of multiple proinflammatory cytokines and chemokines specifically within the brain after E. coli and LPS challenge. Collectively, these data uncover TRIL as a mediator of innate immune responses within the brain, where it enhances neuronal cytokine responses to infection.