Signal transduction activator of transcription 5 (STAT5) dysfunction in autoimmune monocytes and macrophages

Abstract

Autocrine granulocyte macrophage-colony stimulating factor (GM-CSF) sequentially activates intracellular components in monocyte/macrophage production of the pro-inflammatory and immunoregulatory prostanoid, prostaglandin E2 (PGE2). GM-CSF first induces STAT5 signaling protein phosphorylation, then prostaglandin synthase 2 (COX2/PGS2) gene expression, and finally IL-10 production, to downregulate the cascade. Without activation, monocytes of at-risk, type 1 diabetic (T1D), and autoimmune thyroid disease (AITD) humans, and macrophages of nonobese diabetic (NOD) mice have aberrantly high GM-CSF, PGS2, and PGE2 expression, but normal levels of IL-10. After GM-CSF stimulation, repressor STAT5A and B isoforms (80-77 kDa) in autoimmune human and NOD monocytes and activator STAT5A (96-94 kDa) and B (94-92 kDa) isoforms in NOD macrophages stay persistently tyrosine phosphorylated. This STAT5 phosphorylation persisted despite treatment in vitro with IL-10, anti-GM-CSF antibody, or the JAK2/3 inhibitor, AG490. Phosphorylated STAT5 repressor isoforms in autoimmune monocytes had diminished DNA binding capacity on GAS sequences found in the PGS2 gene enhancer. In contrast, STAT5 activator isoforms in NOD macrophages retained their DNA binding capacity on these sites much longer than in healthy control strain macrophages. These findings suggest that STAT5 dysfunction may contribute to dysregulation of GM-CSF signaling and gene activation, including PGS2, in autoimmune monocytes and macrophages.

Functional deficiencies of granulocyte-macrophage colony stimulating factor and interleukin-3 contribute to insulitis and destruction of β cells

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19] These abnormalities appear to reflect cell-intrinsic defects in myeloid cells, resulting in altered numbers or maturation of dendritic cells, macrophages, and granulocytes. However, the contribution of these defects, if any, to diabetes pathogenesis remained unclear.…”

“…The more severe pathologic condition observed in the doubly deficient mice compared with the single knockouts probably reflects some redundancy in signaling through the shared ␤c subunit. 24 Because macrophages from NOD mice and patients with T1D show increased GM-CSF production, 18,19 gene products involved in cytokine receptor signaling or downstream targets are candidates for disease susceptibility loci. Indeed, alterations in STAT5 activity have been reported in patients with T1D and NOD mice.…”

“…5 Among the phenotypic abnormalities observed in patients with T1D and NOD mice are the impaired responses of hematopoietic cells to granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Alterations in the number and/or function of dendritic cells, macrophages, and granulocytes derived from cultures of hematopoietic precursors in GM-CSF and IL-3 have been described, but the contribution of these cytokine defects to altered antigen presenting cell function in vivo and the pathogenesis of diabetes remains unclear.We previously established roles for GM-CSF and IL-3 in the maintenance of immune homeostasis through promoting the efficient phagocytosis of apoptotic cells by macrophages. 20 Consistent with other strains of mice that display an impaired uptake of dying cells, 21 aged GM-CSF and, to a greater extent, GM-CSF/IL-3 doubly deficient mice developed a systemic lupus erythematous (SLE)-like disorder characterized by anti-double-stranded DNA antibodies and immune complex-mediated glomerulonephritis.…”

Nonobese Diabetic Mouse Congenic Analysis Reveals Chromosome 11 Locus Contributing to Diabetes Susceptibility, Macrophage STAT5 Dysfunction, and Granulocyte-Macrophage Colony-Stimulating Factor Overproduction

“…We have shown that monocytes of humans with T1D and autoimmune thyroid diseases as well as NOD mouse monocytes and macrophages have three distinct, but possibly interrelated, phenotypes that can contribute to chronic inflammatory response: 1) aberrantly high expression of the key prostanoid synthesis enzyme, PGS2/cyclooxygenase 2 (COX2) (2, 3); 2) a marked elevation of autocrine GM-CSF production (23,24); and 3) persistent STAT5 phosphorylation (24). In LPS-activated myeloid cells, GM-CSF is an activator of PGS2/COX2 expression, but GM-CSF overproduction alone does not account for the high, IL-10-resistant PGS2/ COX2 expression seen in AI monocytes and NOD macrophages (23,24).…”

“…In LPS-activated myeloid cells, GM-CSF is an activator of PGS2/COX2 expression, but GM-CSF overproduction alone does not account for the high, IL-10-resistant PGS2/ COX2 expression seen in AI monocytes and NOD macrophages (23,24). Although the endogenous GM-CSF production of AI monocytes and macrophages can stimulate high levels of STAT5 phosphorylation, the persistence of phosphorylated STAT5 and its subsequent effects on STAT5 DNA binding characteristics in these cells can become independent of GM-CSF and Jak activity after induction (24). However, the resistance of STAT5 phosphorylation to suppression by IL-10 and its potential effects on IL-10-resistant PGS2/COX2 expression in monocytes and macrophages require at least a brief exposure to GM-CSF (24).…”