Transcription factor ABF-1 suppresses plasma cell differentiation but facilitates memory B cell formation.

Ag-primed B cells that result from an immune response can form either memory B cells or Ab-secreting plasma cells; however, the molecular machinery that controls this cellular fate is poorly understood. In this study, we show that activated B cell factor-1 (ABF-1), which encodes a basic helix-loop-helix transcriptional repressor, participates in this regulation. ABF-1 was prevalently expressed in purified memory B cells and induced by T follicular helper cell-mediated signals. ABF-1 expression declined by the direct repression of B lymphocyte-induced maturation protein-1 during differentiation. Ectopic expression of ABF-1 reduced the formation of Ab-secreting cells in an in vitro differentiation system of human memory B cells. Accordingly, knockdown of ABF-1 potentiates the formation of Ab-secreting cells. A transgenic mouse that expresses inducible ABF-1 in a B cell-specific manner was generated to demonstrate that the formation of germinal center and memory B cells was augmented by induced ABF-1 in an immune response, whereas the Ag-specific plasma cell response was dampened. This effect was associated with the ability of ABF-1 to limit cell proliferation. Together, our results demonstrate that ABF-1 facilitates formation of memory B cells but prevents plasma cell differentiation.

Inducible deletion of the Blimp-1 gene in adult epidermis causes granulocyte-dominated chronic skin inflammation in mice.

B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor important for the differentiation and function of several types of immune cells. Because skin serves as a physical barrier and acts as an immune sentinel, we investigated whether Blimp-1 is involved in epidermal immune function. We show that Blimp-1 expression is reduced in skin lesions of some human eczema samples and in stimulated primary keratinocytes. Epidermal-specific deletion of PR domain containing 1, with ZNF domain (Prdm1), the gene encoding Blimp-1, in adult mice caused spontaneously inflamed skin characterized by massive dermal infiltration of neutrophils/macrophages and development of chronic inflammation associated with higher levels of cytokines/chemokines, including granulocyte colony-stimulating factor (G-CSF), and enhanced myelopoiesis in bone marrow. Deletion of Prdm1 in the epidermis of adult mice also led to stronger inflammatory reactions in a tape-stripping test and in a disease model of contact dermatitis. The elevated G-CSF produced by keratinocytes after deletion of Prdm1 in vitro was mediated by the transcriptional activation of FBJ osteosarcoma oncogene (Fos) and fos-like antigen 1 (Fosl1). Systemic increases in G-CSF contributed to the inflammatory responses, because deletion of the G-CSF gene [colony stimulating factor 3, (Csf3)] prevented neutrophilia and partially ameliorated the inflamed skin in Prdm1-deficient mice. Our findings indicate a previously unreported function for Blimp-1 in restraining steady-state epidermal barrier immunity.

SENP2 restrains the generation of pathogenic Th17 cells in mouse models of colitis.

The molecular mechanisms contributing to the regulation of Th17-mediated inflammation remain underexplored. We here report a SUMO-specific protease (SENP)2-mediated pathway induced in pathogenic Th17 cells that restricts the pathogenesis of inflammatory colitis. SENP2 regulates the maturation of small ubiquitin-like modifiers (SUMO) and recycles SUMO from the substrate proteins. We find higher levels of SENP2 in pathogenic Th17 cells. By deleting Senp2 in T-cell lineages in mice, we demonstrate that the lack of Senp2 exacerbates the severity of experimental colitis, which is linked to elevated levels of GM-CSF+IL-17A+ pathogenic Th17 cells and more severe dysbiosis of the intestinal microbiome. Adoptive transfer experiments demonstrate the cell-autonomous effect of Senp2 in restraining Th17 differentiation and colitis. The enzymatic activity of SENP2 is important for deSUMOylation of Smad4, which reduces Smad4 nuclear entry and Rorc expression. Our findings reveal a SENP2-mediated regulatory axis in the pathogenicity of Th17 cells.

Aberrant distribution and function of plasmacytoid dendritic cells in patients with ankylosing spondylitis are associated with unfolded protein response.

Although human leucocyte antigen (HLA)-B27 is strongly associated with ankylosing spondylitis (AS), the association of unfolded protein response (UPR) induced by HLA-B27 misfolding in AS remains controversial. Since dendritic cells (DCs) are crucial in induction of AS in HLA-B27-transgenic rats, and plasmacytoid DCs (pDCs) belong to one type of DCs, we here aim to study the relevance of pDCs and UPR in AS. Peripheral pDCs were isolated from 27 HLA-B27(+) AS patients and 37 controls. The bone marrow (BM) and synovium of inflamed hips from AS patients and controls were obtained. We found a significantly higher frequency of pDCs in the peripheral blood, BM, or inflamed synovium of hips, which is associated with the enhanced expression of pDC trafficking molecules, CCR6 and CCL20 in the synovium of AS patients. Functional analysis further revealed that several inflammatory cytokines, including TNFα, IL-6, and IL-23, secreted by pDCs were significantly increased in AS patients as compared with those in controls. Remarkably, protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway in UPR was up-regulated in pDCs of AS patients. Notably, PERK inhibitor treatment significantly inhibited the enhanced cytokine production by pDCs of AS patients. Further, the extent of PERK activation was significantly associated with the increased disease severity of AS patients. Our data uncover the aberrant distribution and function of pDCs in AS patients. The up-regulated PERK pathway in UPR of pDCs not only contributes to enhanced cytokine production of pDCs, but also is associated with increased disease activity of AS patients.

HLA-B27-mediated activation of TNAP phosphatase promotes pathogenic syndesmophyte formation in ankylosing spondylitis.

Ankylosing spondylitis (AS) is a type of axial inflammation. Over time, some patients develop spinal ankylosis and permanent disability; however, current treatment strategies cannot arrest syndesmophyte formation completely. Here, we used mesenchymal stem cells (MSCs) from AS patients (AS MSCs) within the enthesis involved in spinal ankylosis to delineate that the HLA-B27-mediated spliced X-box-binding protein 1 (sXBP1)/retinoic acid receptor-ß (RARB)/tissue-nonspecific alkaline phosphatase (TNAP) axis accelerated the mineralization of AS MSCs, which was independent of Runt-related transcription factor 2 (Runx2). An animal model mimicking AS pathological bony appositions was established by implantation of AS MSCs into the lumbar spine of NOD-SCID mice. We found that TNAP inhibitors, including levamisole and pamidronate, inhibited AS MSC mineralization in vitro and blocked bony appositions in vivo. Furthermore, we demonstrated that the serum bone-specific TNAP (BAP) level was a potential prognostic biomarker to predict AS patients with a high risk for radiographic progression. Our study highlights the importance of the HLA-B27-mediated activation of the sXBP1/RARB/TNAP axis in AS syndesmophyte pathogenesis and provides a new strategy for the diagnosis and prevention of radiographic progression of AS.

Suppression of the SOX2 neural effector gene by PRDM1 promotes human germ cell fate in embryonic stem cells.

The mechanisms of transcriptional regulation underlying human primordial germ cell (PGC) differentiation are largely unknown. The transcriptional repressor Prdm1/Blimp-1 is known to play a critical role in controlling germ cell specification in mice. Here, we show that PRDM1 is expressed in developing human gonads and contributes to the determination of germline versus neural fate in early development. We show that knockdown of PRDM1 in human embryonic stem cells (hESCs) impairs germline potential and upregulates neural genes. Conversely, ectopic expression of PRDM1 in hESCs promotes the generation of cells that exhibit phenotypic and transcriptomic features of early PGCs. Furthermore, PRDM1 suppresses transcription of SOX2. Overexpression of SOX2 in hESCs under conditions favoring germline differentiation skews cell fate from the germline to the neural lineage. Collectively, our results demonstrate that PRDM1 serves as a molecular switch to modulate the divergence of neural or germline fates through repression of SOX2 during human development.

The effects of glycine transporter I inhibitor, N-methylglycine (sarcosine), on ketamine-induced alterations in sensorimotor gating and regional brain c-Fos expression in rats.

Reduced N-methyl-D-aspartate receptor (NMDAR) function may contribute to the pathogenesis of schizophrenia. Sarcosine, a potent glycine transporter inhibitor, can increase synaptic glycine and then promote NMDAR function. We assessed the antipsychotic potential of sarcosine by comparing the abilities of sarcosine and clozapine to restore the prepulse inhibition (PPI) deficit, hyperlocomotion and regional brain c-Fos expression changes caused by an NMDAR antagonist, ketamine. Four groups of rats were given acute injections, including saline+saline, saline+30 mg/kg ketamine, 100mg/kg sarcosine+30 mg/kg ketamine, and 15 mg/kg clozapine+30 mg/kg ketamine. Both sarcosine and clozapine reversed the ketamine-induced PPI deficit and hyperlocomotion. They both did not change ketamine-induced increase in c-Fos expression in the prefrontal cortex and nucleus accumbens. However, in the olfactory bulb, sarcosine, but not clozapine, significantly reduced the ketamine-induced increase in c-Fos expression. Our animal study demonstrated that sarcosine may have antipsychotic potential.