Bhlhe40 mediates tissue-specific control of macrophage proliferation in homeostasis and type 2 immunity.

Most tissue-resident macrophage populations develop during embryogenesis, self-renew in the steady state and expand during type 2 immunity. Whether shared mechanisms regulate the proliferation of macrophages in homeostasis and disease is unclear. Here we found that the transcription factor Bhlhe40 was required in a cell-intrinsic manner for the self-renewal and maintenance of large peritoneal macrophages (LPMs), but not that of other tissue-resident macrophages. Bhlhe40 was necessary for the proliferation, but not the polarization, of LPMs in response to the cytokine IL-4. During infection with the helminth Heligmosomoides polygyrus bakeri, Bhlhe40 was required for cell cycling of LPMs. Bhlhe40 repressed the expression of genes encoding the transcription factors c-Maf and Mafb and directly promoted expression of transcripts encoding cell cycle-related proteins to enable the proliferation of LPMs. In LPMs, Bhlhe40 bound to genomic sites co-bound by the macrophage lineage-determining factor PU.1 and to unique sites, including Maf and loci encoding cell-cycle-related proteins. Our findings demonstrate a tissue-specific control mechanism that regulates the proliferation of resident macrophages in homeostasis and type 2 immunity.

Transcription Factor Bhlhe40 in Immunity and Autoimmunity.

The basic helix-loop-helix transcription factor (TF) Bhlhe40 is emerging as a key regulator of immunity during infection, autoimmunity, and inflammatory conditions. We describe the roles of Bhlhe40 in the circulating and tissue-resident arms of the immune system, with emphasis on recent work on the regulation of cytokine production and proliferation. We explore the mechanisms behind these functions in mouse models and human cells, including interactions with other TFs, and propose that Bhlhe40 is a central mediator of both inflammation and pathogen control, as well as a crucial regulator of a growing number of tissue-resident leukocyte populations. Finally, we suggest areas for further study that may advance our understanding of immunity and disease.

BHLHE40 Promotes TH2 Cell-Mediated Antihelminth Immunity and Reveals Cooperative CSF2RB Family Cytokines.

The transcription factor BHLHE40 is an emerging regulator of the immune system. Recent studies suggest that BHLHE40 regulates type 2 immunity, but this has not been demonstrated in vivo. We found that BHLHE40 is required in T cells for a protective TH2 cell response in mice infected with the helminth Heligmosomoides polygyrus bakeri H. polygyrus elicited changes in gene and cytokine expression by lamina propria CD4+ T cells, many of which were BHLHE40 dependent, including production of the common ß (CSF2RB) chain family cytokines GM-CSF and IL-5. In contrast to deficiency in GM-CSF or IL-5 alone, loss of both GM-CSF and IL-5 signaling impaired protection against H. polygyrus Overall, we show that BHLHE40 regulates the TH2 cell transcriptional program during helminth infection to support normal expression of Csf2, Il5, and other genes required for protection and reveal unexpected redundancy of common ß chain-dependent cytokines previously thought to possess substantially divergent functions.

BHLHE40 Mediates Cross-Talk between Pathogenic TH17 Cells and Myeloid Cells during Experimental Autoimmune Encephalomyelitis.

TH17 cells are implicated in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). We previously reported that the transcription factor basic helix-loop-helix family member e40 (BHLHE40) marks cytokine-producing pathogenic TH cells during EAE, and that its expression in T cells is required for clinical disease. In this study, using dual reporter mice, we show BHLHE40 expression within TH1/17 and ex-TH17 cells following EAE induction. Il17a-Cre-mediated deletion of BHLHE40 in TH cells led to less severe EAE with reduced TH cell cytokine production. Characterization of the leukocytes in the CNS during EAE by single-cell RNA sequencing identified differences in the infiltrating myeloid cells when BHLHE40 was present or absent in TH17 cells. Our studies highlight the importance of BHLHE40 in promoting TH17 cell encephalitogenicity and instructing myeloid cell responses during active EAE.

The ZFP36 family of RNA binding proteins regulates homeostatic and autoreactive T cell responses.

RNA binding proteins are important regulators of T cell activation, proliferation, and cytokine production. The zinc finger protein 36 (ZFP36) family genes (Zfp36, Zfp36l1, and Zfp36l2) encode RNA binding proteins that promote the degradation of transcripts containing AU-rich elements. Numerous studies have demonstrated both individual and shared functions of the ZFP36 family in immune cells, but their collective function in T cells remains unclear. Here, we found a redundant and critical role for the ZFP36 proteins in regulating T cell quiescence. T cell-specific deletion of all three ZFP36 family members in mice resulted in early lethality, immune cell activation, and multiorgan pathology characterized by inflammation of the eyes, central nervous system, kidneys, and liver. Mice with T cell-specific deletion of any two Zfp36 genes were protected from this spontaneous syndrome. Triply deficient T cells overproduced proinflammatory cytokines, including IFN-γ, TNF, and GM-CSF, due to increased mRNA stability of these transcripts. Unexpectedly, T cell-specific deletion of both Zfp36l1 and Zfp36l2 rendered mice resistant to experimental autoimmune encephalomyelitits due to failed priming of antigen-specific CD4+ T cells. ZFP36L1 and ZFP36L2 double-deficient CD4+ T cells had poor proliferation during in vitro T helper cell polarization. Thus, the ZFP36 family redundantly regulates T cell quiescence at homeostasis, but ZFP36L1 and ZFP36L2 are specifically required for antigen-specific T cell clonal expansion.

Synthesis and anti-cancer activities of a water soluble gold(III) porphyrin.

Gold(III) compounds continue to be explored for their potential utility as anticancer agents. A recognized limitation is the reactivity of gold(III), which is typically reduced to the more labile gold(I) state under physiological conditions. The use of porphyrins can overcome this problem. However, to date the stabilization provided by the use a strongly chelating porphyrin is offset by the poor solubility of the resulting complex in aqueous media. In this work, we describe the synthesis and in vitro anti-cancer activity of a gold(III)porphyrin complex with relatively good aqueous solubility. As judged from standard antiproliferation assays, this complex displays an IC50 of 9 µM for the A2780 human ovarian cancer cell line. This is a higher level of potency than displayed by two related control systems.