Purna Krishnamurthy

Increased Th2 activity and diminished skin barrier function cooperate in allergic skin inflammation.

Atopic dermatitis (AD) is a chronic inflammatory skin disease induced by a complex interaction between susceptibility genes encoding skin barrier components and environmental allergen exposure that results in type 2 cytokine production. Although genetic lesions in either component can be risk factors for disease in patients, whether these pathways interact in the development of AD is not clear. To test this, we mated mice with T‐cell specific expression of constitutively active Stat6 (Stat6VT) that spontaneously develop allergic skin inflammation with Flaky tail (Ft) mice that have mutations in Flg and Tmem79 genes that each affect skin barrier function. Our results demonstrate that over 90% of the Stat6VT transgenic mice carrying the Ft alleles (Stat6VTxFt−/−) develop severe atopic dermatitis lesions by 3–5 months of age, compared with only 40% of Stat6VT mice that develop disease by 6–7 months of age. Further, histopathological analysis of skin tissues from Stat6VTxFt−/− mice revealed extensive thickening of the dermis with increased inflammatory infiltrates as compared with Stat6VT mice. Our study suggests that skin barrier defects and altered Th2 responses independently cooperate in the pathogenesis of allergic skin inflammation, similar to effects observed in patients with AD.

Poly‐ADP‐ribosyl polymerase‐14 promotes T helper 17 and follicular T helper development

Transcription factors are critical determinants of T helper cell fate and require a variety of co‐factors to activate gene expression. We previously identified the ADP ribosyl‐transferase poly‐ADP‐ribosyl polymerase 14 (PARP‐14) as a co‐factor of signal transducer and activator of transcription (STAT) 6 that is important in B‐cell and T‐cell responses to interleukin‐4, particularly in the differentiation of T helper type 2 (Th2) cells. However, whether PARP‐14 functions during the development of other T helper subsets is not known. In this report we demonstrate that PARP‐14 is highly expressed in Th17 cells, and that PARP‐14 deficiency and pharmacological blockade of PARP activity result in diminished Th17 differentiation in vitro and in a model of allergic airway inflammation. We further show that PARP‐14 is expressed in T follicular helper (Tfh) cells and Tfh cell development is impaired in PARP‐14‐deficient mice following immunization with sheep red blood cells or inactivated influenza virus. Decreases in Th17 and Tfh development are correlated with diminished phospho‐STAT3 and decreased expression of the interleukin‐6 receptor α‐chain in T cells. Together, these studies demonstrate that PARP‐14 regulates multiple cytokine responses during inflammatory immunity.

Poly-ADP ribose polymerase-14 limits severity of allergic skin disease

Poly‐ADP ribose polymerase‐14 (PARP14 or ARTD8) was initially identified as a transcriptional co‐activator for signal transducer and activator of transcription 6 (Stat6), where the presence of interleukin‐4 (IL‐4) and activated Stat6 induces the enzymatic activity of PARP14 that promotes T helper type 2 differentiation and allergic airway disease. To further our understanding of PARP14 in allergic disease, we studied the function of PARP14 in allergic inflammation of skin using mice that express constitutively active Stat6 in T cells (Stat6VT) and develop spontaneous inflammation of the skin. We mated Stat6VT mice to Parp14−/− mice and observed that approximately 75% of the Stat6VT × Parp14−/− mice develop severe atopic dermatitis (AD)‐like lesions, compared with about 50% of Stat6VT mice, and have increased morbidity compared with Stat6VT mice. Despite this, gene expression in the skin and the cellular infiltrates was only modestly altered by the absence of PARP14. In contrast, we saw significant changes in systemic T‐cell cytokine production. Moreover, adoptive transfer experiments demonstrated that decreases in IL‐4 production reflected a cell intrinsic role for PARP14 in Th2 cytokine control. Hence, our data suggest that although PARP14 has similar effects on T‐cell cytokine production in several allergic disease models, the outcome of those effects is distinct, depending on the target organ of disease.

STAT4 deficiency reduces the development of atherosclerosis in mice

Atherosclerosis is a chronic inflammatory process that leads to plaque formation in large and medium sized vessels. T helper 1 (Th1) cells constitute the majority of plaque infiltrating pro-atherogenic T cells and are induced via IFNγ-dependent activation of T-box (Tbet) and/or IL-12-dependent activation of signal transducer and activator of transcription 4 (STAT4). We thus aimed to define a role for STAT4 in atherosclerosis. STAT4-deficiency resulted in a ∼71% reduction (p < 0.001) in plaque burden in Stat4(-/-)Apoe(-/-) vs Apoe(-/-) mice fed chow diet and significantly attenuated atherosclerosis (∼31%, p < 0.01) in western diet fed Stat4(-/-)Apoe(-/-) mice. Surprisingly, reduced atherogenesis in Stat4(-/-)Apoe(-/-) mice was not due to attenuated IFNγ production in vivo by Th1 cells, suggesting an at least partially IFNγ-independent pro-atherogenic role of STAT4. STAT4 is expressed in T cells, but also detected in macrophages (MΦs). Stat4(-/-)Apoe(-/-)in vitro differentiated M1 or M2 MΦs had reduced cytokine production compare to Apoe(-/-) M1 and M2 MΦs that was accompanied by reduced induction of CD69, I-A(b), and CD86 in response to LPS stimulation. Stat4(-/-)Apoe(-/-) MΦs expressed attenuated levels of CCR2 and demonstrated reduced migration toward CCL2 in a transwell assay. Importantly, the percentage of aortic CD11b(+)F4/80(+)Ly6C(hi) MΦs was reduced in Stat4(-/-)Apoe(-/-) vs Apoe(-/-) mice. Thus, this study identifies for the first time a pro-atherogenic role of STAT4 that is at least partially independent of Th1 cell-derived IFNγ, and primarily involving the modulation of MΦ responses.