The maintenance of regulatory T (T reg ) cells critically prevents autoimmunity. Pre–B cell leukemia transcription factor 1 ( Pbx1 ) variants are associated with lupus susceptibility, particularly through the expression of a dominant negative isoform Pbx1-d in CD4 + T cells. Pbx1-d overexpression impaired T reg cell homeostasis and promoted inflammatory CD4 + T cells. Here, we showed a high expression of Pbx1 in human and murine T reg cells, which is decreased in lupus patients and mice. Pbx1 deficiency or Pbx1-d overexpression reduced the number, stability, and suppressive activity of T reg cells, which increased murine responses to immunization and autoimmune induction. Mechanistically, Pbx1 deficiency altered the expression of genes implicated in cell cycle and apoptosis in T reg cells. Intriguingly, Rtkn2 , a Rho-GTPase previously associated with T reg homeostasis, was directly transactivated by Pbx1. Our results suggest that the maintenance of T reg cell homeostasis and stability by Pbx1 through cell cycle progression prevent the expansion of inflammatory T cells that otherwise exacerbates lupus progression in the hosts.

Pre-B cell leukemia homeobox 1 (PBX1) controls chromatin accessibility to a large number of genes in various cell types. Its dominant negative splice isoform, PBX1D, which lacks the DNA and Hox-binding domains, is expressed more frequently in the CD4+ T cells from lupus-prone mice and patients with systemic lupus erythematosus than healthy control subjects. PBX1D overexpression in CD4+ T cells impaired regulatory T cell homeostasis and expanded inflammatory CD4+ T cells. In this study, we showed that PBX1 message expression is downregulated by activation in CD4+ T cells as well as in B cells. PBX1D protein was less stable than the normal isoform, PBX1B, and it is degraded through the ubiquitin-proteasome-dependent pathway. The DNA binding domain lacking in PBX1D has two putative ubiquitin binding sites, K292 and K293, that are predicted to be in direct contact with DNA. Mutation of K292-293 reduced PBX1B stability to a level similar to PBX1D and abrogated DNA binding. In addition, contrary to PBX1B, PBX1D is retained in the cytoplasm without the help of the cofactors MEIS or PREP1, indicating a different requirement for nuclear translocation. Overall, these findings suggest that multiple post-transcriptional mechanisms are responsible for PBX1D loss of function and induction of CD4+ T cell inflammatory phenotypes in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease in which poorly characterized genetic factors lead to the production of proinflammatory or autoreactive T cells. Pre-B cell leukemia homeobox 1 (PBX1) is a transcription factor whose dominant negative isoform (PBX1-D) is overexpressed in the CD4+ T cells of SLE patients and lupus-prone mice. Pbx1-D overexpression favors the expansion of proinflammatory T cells and impairs regulatory T (Treg) cell development. Here we show that Pbx1 deficiency and Pbx1-D overexpression decreased STAT3 expression and activation in T cells. Accordingly, Pbx1 deficiency in T cells and Pbx1-D overexpression reduced STAT3-dependent TH17 cell polarization in vitro, but it had no effect in vivo at steady state. STAT3-dependent follicular helper T (TFH) cell polarization in vitro and splenic TFH cell frequency were not affected by either Pbx1 deficiency or Pbx1-D overexpression. Pbx1 deficiency also increased the expression of cell cycle arrest and pro-apoptotic genes, with an increased apoptosis in T cells. Our results suggest a complex interplay between PBX1 and STAT3, which may contribute to lupus pathogenesis through dysregulation of the cell cycle and apoptosis.

The pre-B cell leukemia homeobox1 (Pbx1) controls chromatin accessibility to a large number of genes in various cell types. Its dominant negative splice isoform, Pbx1-d that lacks the DNA and Hox-binding domains, is expressed more frequently in the CD4 +T cells from lupus-prone mice and SLE patients than healthy controls. We have shown that overexpression of Pbx1-d in CD4 +T cells impaired Treg cell homeostasis and expanded inflammatory CD4 +T cells. Here, we investigated the molecular mechanisms by which PBX1 regulates T cells. We showed that PBX1 is preferentially expressed in Treg cells over other CD4+ T cell subsets, and that it is negatively regulated by TCR activation. Furthermore, PBX1-D protein was less stable than the normal isoform, PBX1-B, in a pulse chase experiment. PBX1-B but not PBX1-D has two predictive ubiquitin binding sites, K292 and K293, located in the DNA binding domain. Mutation of these two sites reduced PBX1-B stability to a level similar to PBX1-D, suggesting that a loss of function in the lupus associated allele through the ubiquitin-proteasome dependent pathway. In addition, contrary to PBX1-B, PBX1-D is retained in the cytoplasm without the help of the MEIS or PREP1 co-factors, indicating different requirements for nuclear translocation. Overall, these findings suggest that multiple transcriptional and post-transcriptional mechanisms are responsible for PBX1-D loss of function and induction of CD4 +T cell inflammatory phenotypes in SLE. This work was supported by National Institutes of Health Grants AI045050

Systemic Lupus Erythematosus (SLE) is an autoimmune disease in which poorly characterized genetic factors lead to the production of autoreactive or inflammatory T cells. Pre-B cell leukemia homeobox 1 (Pbx1) is a transcription factor whose dominant negative splice isoform (Pbx1-D) is overexpressed in CD4 T cells of lupus patients and lupus-prone mice as compared to the normal isoform (Pbx1-B). Pbx1-D overexpression impairs Treg cell development and function while favoring the production of follicular helper T cells. Based on previous studies showing that Pbx1 promotes cell proliferation via JAK2/STAT3 signaling pathway in a renal cell carcinoma, we hypothesized that Pbx1-D decreases T cell proliferation and viability by attenuating the JAK2/STAT3 signaling pathway. U3A STAT3 reporter cells transfected with Pbx1-B plasmid have a greater luciferase expression, and hence pSTAT3 transcriptional activity in comparison to cells transfected with Pbx1-D or control plasmids. We also observed that Jurkat T cells stably overexpressing Pbx1-B increases STAT3 gene expression as compared to Pbx1-D. Furthermore, Pbx1 silencing in Jurkat T cells leads to the attenuation of STAT3 message. These results suggest a mechanism by which Pbx1 contributes to impaired T cells in lupus pathogenesis is via the JAK2/STAT3 pathway. Current studies are conducted to dissect the mechanism by which Pbx1 regulates this pathway in primary T cells. Supported by a grant from the NIH (R01 AI045050) to LM.

Pre-B cell leukemia transcription factor 1 (Pbx1) regulates multiple processes in various cell types. The Pbx1 gene is located in the Sle1a1 lupus susceptibility locus in the NZM2410 lupus-prone mouse model. The Pbx1-d dominant negative isoform lacking the DNA binding domain is more frequent in the CD4+ T cells from NZM240 mice as well as lupus patients as compared to healthy controls. In addition, the transgenic expression of Pbx1-d in CD4+ T cells reproduced the phenotypes of Sle1a1 mice, with impaired Foxp3+ Treg cell homeostasis as well as increased inflammatory CD4+ T cells. To study the role of Pbx1 in Treg cells, we generated Foxp3-specific Pbx1 knock-out mice (Foxp3-Pbx1 KO), which were bred to CD4-Pbx1-d-Tg mice to generate Pbx1-d Tg-KO mice that have Treg cells solely expressing Pbx1-d. Foxp3-Pbx1 KO mice showed reduced numbers of Treg cells with impaired suppressive activity. The numbers of natural Treg (nTrg) cells are decreased in thymus but not in spleen of Foxp3-Pbx1 KO mice, while the number of induced Treg (iTreg) cells are increased in the thymus and decreased in the periphery, suggesting that Pbx1 regulates Treg cell development and stability. The results were enhanced in Pbx1-d Tg-KO mice compared with Foxp3-Pbx1 KO mice, leading to autoimmune phenotypes, suggesting that the expression of Pbx1 functional isoform is necessary for the maintenance and function of Treg cells. RNAseq analyses with Pbx1-KO Treg cells indicated that Pbx1 regulates cell cycle, apoptosis and migration. Overall, our results suggest that Pbx1 regulates Treg cell homeostasis, stability and their suppressive functions and that Pbx1-d promotes lupus development by decreasing Treg cell development and functions. Supported by a grant from the NIH (R01 AI045050)

Immune homeostasis is a constant balancing act between effector T cells and regulatory T cells defined by Foxp3 expression, the transcription factor that drives their differentiation and immunosuppressive activity. Immune homeostasis is altered when Treg cells are not generated or maintained in sufficient numbers. Treg cells rendered unstable by loss of Foxp3 expression, known as ex-Treg cells, gain pro-inflammatory functions. Treg cells may also become dysfunctional and lose their suppressive capabilities. These alterations can cause an imbalance between effector and regulatory subsets, which may ultimately lead to autoimmunity. This review discusses recent studies that identified genetic factors that maintain Treg cell stability as well as preserve their suppressive function. We focus on studies associated with systemic lupus erythematosus and highlight their findings in the context of potential therapeutic gene targeting in Treg cells to reverse the phenotypic changes and functional dysregulation inducing autoimmunity.

Systemic lupus erythematosus (SLE) is an autoimmune disease in which the overactivation of the immune system has been associated with metabolic alterations. Targeting the altered immunometabolism has been proposed to treat SLE patients based on their results obtained and mouse models of the disease. Here, we review the recent literature to discuss the possible origins of the alterations in the metabolism of immune cells in lupus, the dominant role of mitochondrial defects, technological advances that may move the field forward, as well as how targeting lupus immunometabolism may have therapeutic potential.

Background Lupus progression is driven by the aberrant activation of T and B lymphocytes which promote a dysregulated cytokine milieu and produce pathogenic antibodies. Many cytokines, including interferon gamma (IFN-γ), utilize the janus kinase/signal transduction and activation of transcription (JAK/STAT) pathway for signal propagation. Suppressor of Cytokine Signaling-1 (SOCS-1) is an inducible, intracellular protein which regulates the JAK/STAT pathway and IFNγ signaling. We have previously shown that a peptide mimicking the kinase inhibitory region of SOCS1 (SOCS1-KIR) inhibited IFN-γ signaling and inflammation-mediated disease progression. Using MRL/lpr mice, which spontaneously develop SLE-like disease, we test the hypothesis that SOCS1-KIR administration inhibits T and B lymphocyte activation leading to an amelioration in lupus pathology. Methods Female MRL/lpr mice received intraperitoneal injections of SOCS1-KIR peptide, or PBS carrier, 3 times per week and were monitored for lupus-like disease progression. Disease progression was based on the presence of skin lesions, lymphadenopathy, overall body score, and proteinuria. Peripheral blood, lymph nodes, and spleen was evaluated for peptide-mediated changes in lymphocyte populations by flow cytometry and qPCR. ELISA and western blot analysis were also employed to assess changes in lymphocyte activation. Finally, peptide mediated changes in renal pathology were analyzed. Results We show that intraperitoneal administration of SOCS1-KIR reduced the frequency, activation, and cytokine production of memory CD8+ and CD4+ T lymphocytes within the peripheral blood, spleen, and lymph nodes of treated mice. In addition, administration of SOCS1-KIR mimetic peptide treatment reduced lymphadenopathy, delayed the development and severity of skin lesions, reduced autoantibody production, and lupus associated kidney destruction. On a cellular level, SOCS1-KIR administration enhanced Foxp3 expression in both total splenic Tregs and follicular Tregs (figure 1). In addition, SOCS1-KIR treatment reduced the frequency of GL7+ germinal center enriched B cells and CD80+ leukocytes, which may potentially activate T lymphocytes. Conclusion Together, these data show that SOCS1-KIR treatment was effective in reducing auto-reactive lymphocyte effector functions and suggest that therapeutic targeting of the SOCS1 pathway through peptide administration may have efficacy in mitigating lupus progression. Acknowledgement We thank Mr. Benson and Dr. Moneypenny for flow cytometry assistance, UF animal care, and Drs. Hoffman and Wilson for technical expertise. This study was supported by the Lupus Research Institute, National Psoriasis Foundation, a BD Biosciences Research Grant, NIH/NCATS Clinical and Translational Science Awards TL1 TR000066 and UL1TR000064, NIH/NIAID subaward U01AI101990 and The Mcknight Fellowship Foundation.

Autoimmune diseases are driven largely by a pathogenic cytokine milieu produced by aberrantly activated lymphocytes. Many cytokines, including interferon gamma (IFN-γ), utilize the JAK/STAT pathway for signal propagation. Suppressor of Cytokine Signaling-1 (SOCS1) is an inducible, intracellular protein that regulates IFN-γ signaling by dampening JAK/STAT signaling. Using Fas deficient, MRL/MpJ-Fas lpr /J (MRL/lpr) mice, which develop lupus-like disease spontaneously, we tested the hypothesis that a peptide mimic of the SOCS1 kinase inhibitory region (SOCS1-KIR) would inhibit lymphocyte activation and modulate lupus-associated pathologies. Consistent with in vitro studies, SOCS1-KIR intraperitoneal administration reduced the frequency, activation, and cytokine production of memory CD8 + and CD4 + T lymphocytes within the peripheral blood, spleen, and lymph nodes. In addition, SOCS1-KIR administration reduced lymphadenopathy, severity of skin lesions, autoantibody production, and modestly reduced kidney pathology. On a cellular level, peritoneal SOCS1-KIR administration enhanced Foxp3 expression in total splenic and follicular regulatory T cells, reduced the effector memory/naïve T lymphocyte ratio for both CD4 + and CD8 + cells, and reduced the frequency of GL7 + germinal center enriched B cells. Together, these data show that SOCS1-KIR treatment reduced auto-reactive lymphocyte effector functions and suggest that therapeutic targeting of the SOCS1 pathway through peptide administration may have efficacy in mitigating autoimmune pathologies.

Systemic Lupus Erythematosus (SLE) is an autoimmune disease in which poorly characterized genetic factors lead to the production of autoreactive or inflammatory T cells. Pre-B cell leukemia homeobox 1 (Pbx1) is a transcription factor whose dominant negative splice isoform (Pbx1-D) is overexpressed in CD4 T cells of lupus patients and lupus-prone mice as compared to the normal isoform (Pbx1-B). Pbx1-D overexpression impairs Treg cell development and function while favoring the production of follicular helper T cells. Based on previous studies showing that Pbx1 promotes cell proliferation via JAK2/STAT3 signaling pathway in a renal cell carcinoma, we hypothesized that Pbx1-D decreases T cell proliferation and viability by attenuating the JAK2/STAT3 signaling pathway. Pbx1-B or Pbx1-D expression plasmids increased pSTAT3 protein levels but there was no difference between the two isoforms in 293T cells. U3A STAT3 reporter cells transfected with Pbx1-B plasmid have greater luciferase expression, and hence pSTAT3 transcriptional activity in comparison to cells transfected with Pbx1-D or control plasmids. We also observed that Pbx1-B increases the expression of Jak2 and Stat3 message as compared to Pbx1-D. These results suggest a mechanism by which Pbx1 contributes to impaired T cells in lupus pathogenesis is via the JAK2/STAT3 pathway. Current studies are conducted to dissect the mechanism by which Pbx1 regulates this pathway in primary T cells. Supported by a grant from the NIH (RO1AI04505021) to LM

Systemic Lupus Erythematosus (SLE) is an autoimmune disease that affects many organ systems. Poorly characterized genetic factors contribute to SLE, in part through the production of autoreactive or inflammatory T cells. Pre-B cell leukemia homeobox 1 (Pbx1) is a transcription factor whose Pbx1-d dominant negative splice isoform is overexpressed in CD4T cells of lupus patients as well as in the NZM2410 lupus-prone mouse as compared to the normal Pbx1-b isoform. Based on gene expression studies comparing murine CD4 T cells overexpressing Pbx1-d to controls, we hypothesize that Pbx1-d enhances cellular metabolism in T cells through the HIF1α and mTORc1 pathways. CD4 T cells expressing Pbx1-d present a higher cellular metabolism and show a higher mTORc1 activation than normal control T cells. Using mesenchymal stem cells, we showed that transfection of Pbx1-d was sufficient to increase glycolysis, a pathway linked to T cell activation. We found that Ddit4, an mTORc1 inhibitor, shows a lower expression in the Pbx1-d-expressing CD4 T cells than in normal T cells. We also discovered that Pbx1-d preferentially binds to the promoter of Ddit4, as well as Egln1 and Egln3, two HIF1a inhibitors. These results suggest that a mechanism by which the Pbx1-d allele contributes to lupus pathogenesis is to enhance CD4 T cell metabolism. Future work will define how Pbx1 controls the immune system and how the function of this transcription factor is linked to cellular metabolism.

Background Ocular abnormalities present in microcephalic infants with presumed Zika virus (ZIKV) congenital disease includes focal pigment mottling of the retina, chorioretinal atrophy, optic nerve abnormalities, and lens dislocation. Target cells in the ocular compartment for ZIKV infectivity are unknown. The cellular response of ocular cells to ZIKV infection has not been described. Mechanisms for viral dissemination in the ocular compartment of ZIKV-infected infants and adults have not been reported. Here, we identify target cells for ZIKV infectivity in both the inner and outer blood-retinal barriers (IBRB and OBRB), describe the cytokine expression profile in the IBRB after ZIKV exposure, and propose a mechanism for viral dissemination in the retina. Methods We expose primary cellular components of the IBRB including human retinal microvascular endothelial cells, retinal pericytes, and Müller cells as well as retinal pigmented epithelial cells of the OBRB to the PRVABC56 strain of ZIKV. Viral infectivity was analyzed by microscopy, immunofluorescence, and reverse transcription polymerase chain reaction (RT-PCR and qRT-PCR). Angiogenic and proinflammatory cytokines were measured by Luminex assays. Results We find by immunofluorescent staining using the Flavivirus 4G2 monoclonal antibody that retinal endothelial cells and pericytes of the IBRB and retinal pigmented epithelial cells of the OBRB are fully permissive for ZIKV infection but not Müller cells when compared to mock-infected controls. We confirmed ZIKV infectivity in retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells by RT-PCR and qRT-PCR using ZIKV-specific oligonucleotide primers. Expression profiles by Luminex assays in retinal endothelial cells infected with ZIKV revealed a marginal increase in levels of beta-2 microglobulin (β2-m), granulocyte macrophage colony-stimulating factor (GMCSF), intercellular adhesion molecule 1 (ICAM-1), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP1), and vascular cell adhesion molecule 1 (VCAM-1) and higher levels of regulated upon activation, normal T cell expressed and presumably secreted (RANTES) but lower levels of interleukin-4 (IL-4) compared to controls. Conclusions Retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells are fully permissive for ZIKV lytic replication and are primary target cells in the retinal barriers for infection. ZIKV infection of retinal endothelial cells and retinal pericytes induces significantly higher levels of RANTES that likely contributes to ocular inflammation.