Enteric glial cells (EGCs) of the enteric nervous system are critically involved in the maintenance of intestinal epithelial barrier function (IEB). The underlying mechanisms remain undefined. Glial cell line-derived neurotrophic factor (GDNF) contributes to IEB maturation and may therefore be the predominant mediator of this process by EGCs. Using GFAP^cre x Ai14^floxed mice to isolate EGCs by Fluorescence-activated cell sorting (FACS), we confirmed that they synthesize GDNF in vivo as well as in primary cultures demonstrating that EGCs are a rich source of GDNF in vivo and in vitro. Co-culture of EGCs with Caco2 cells resulted in IEB maturation which was abrogated when GDNF was either depleted from EGC supernatants, or knocked down in EGCs or when the GDNF receptor RET was blocked. Further, TNFα-induced loss of IEB function in Caco2 cells and in organoids was attenuated by EGC supernatants or by recombinant GDNF. These barrier-protective effects were blunted when using supernatants from GDNF-deficient EGCs or by RET receptor blockade. Together, our data show that EGCs produce GDNF to maintain IEB function in vitro through the RET receptor.

Mycosis fungoides (MF) is a rare cutaneous T cell lymphoma that, in its early stages, can closely mimic eczema and psoriasis in both clinical appearance and histopathologic features, leading to frequent misdiagnosis, inappropriate treatment, and delayed care. Reliable adjunctive biomarkers are lacking, underscoring the need for improved diagnostic strategies. We developed a biomarker discovery framework based on bulk RNA sequencing of skin biopsies (19 MF, 112 psoriasis, 105 eczema), which identified seven candidate diagnostic genes. RT-PCR analysis in FFPE tissue specimens from 65 MF and 101 eczema/psoriasis samples verified LCK and HOMER1 as robust discriminator genes. A logistic regression model based on LCK and HOMER1 gene expression differentiated MF from psoriasis and eczema with 91% sensitivity and 94% specificity. Independent validation on 7 additional international cohorts (MF n=58, eczema/psoriasis n=55) confirmed robust performance. Spatial and single-cell transcriptomic analyses revealed biological underpinnings of classifier accuracy: LCK was enriched in malignant and specific T cell subsets in MF, whereas HOMER1 was confined to keratinocytes in eczema and psoriasis but nearly absent in MF. Case studies demonstrated that the classifier identified MF in routine biopsies earlier than histopathology. This molecular diagnostic approach enables earlier and more reliable distinction of MF from common inflammatory dermatoses, offering a clinically applicable tool to reduce diagnostic uncertainty, accelerate appropriate treatment, and might improve patient outcomes. One Sentence Summary: A two-gene classifier reliably distinguishes mycosis fungoides from eczema and psoriasis, enabling early and accurate diagnosis.