Longitudinal analysis of sarcoidosis blood transcriptomic signatures and disease outcomes.

Previously, we demonstrated concordance in differentially expressed genes in sarcoidosis blood and lung, implicating shared dysfunction of specific immune pathways. In the present study, we hypothesised that expression levels of candidate genes in sarcoidosis blood could predict and track with disease outcomes longitudinally. We applied Ingenuity Pathway Analysis to a cross-sectional derivation microarray dataset (n=38) to identify canonical pathways and candidate genes associated with sarcoidosis. In a separate longitudinal sarcoidosis cohort (n=103), we serially measured 48 candidate gene transcripts, and assessed their relation to disease chronicity and severity. In the cross-sectional derivation study, pathway analysis showed upregulation of genes related to interferon signalling and the role of pattern recognition receptors, and downregulation of T-cell receptor (TCR) signalling pathways in sarcoidosis. In the longitudinal cohort, factor analysis confirmed coregulation of genes marking these pathways and identified CXCL9 as an additional candidate pathway. CXCL9 and TCR factors discriminated between chronic versus nonprogressive disease, and CXCL9 predicted disease outcomes longitudinally. Interferon factor was similarly increased in both disease phenotypes. Factors associated with lung function decline included decreased TCR factor and increased CXCL9. These findings demonstrate blood transcriptomic signatures reflecting TCR signalling and CXCL9 predict sarcoidosis chronicity and correlate with disease severity longitudinally.

ALCAM regulates mediolateral retinotopic mapping in the superior colliculus.

ALCAM [activated leukocyte cell adhesion molecule (BEN/SC-1/DM-GRASP)] is a transmembrane recognition molecule of the Ig superfamily (IgSF) containing five Ig domains (two V-type, three C2-type). Although broadly expressed in the nervous and immune systems, few of its developmental functions have been elucidated. Because ALCAM has been suggested to interact with the IgSF adhesion molecule L1, a determinant of retinocollicular mapping, we hypothesized that ALCAM might direct topographic targeting to the superior colliculus (SC) by serving as a substrate within the SC for L1 on incoming retinal ganglion cell (RGC) axons. ALCAM was expressed in the SC during RGC axon targeting and on RGC axons as they formed the optic nerve; however, it was downregulated distally on RGC axons as they entered the SC. Axon tracing with DiI revealed pronounced mistargeting of RGC axons from the temporal retina half of ALCAM null mice to abnormally lateral sites in the contralateral SC, in which these axons formed multiple ectopic termination zones. ALCAM null mutant axons were specifically compromised in medial orientation of interstitial branches, which is known to require the ankyrin binding function of L1. As a substrate, ALCAM-Fc protein promoted L1-dependent attachment of acutely dissociated retinal cells and an L1-expressing, ALCAM-negative cell line, consistent with an ALCAM-L1 heterophilic molecular interaction. Together, these results suggest a model in which ALCAM in the SC interacts with L1 on RGC axons to promote medial extension of RGC axon branches important for mediolateral axon targeting in the formation of retinocollicular maps.