Ectopic co-expression of canonical and LINE1 and THE1A-exonizing IL23R transcripts in sarcoid myopathy.

Sarcoidosis is a heterogenous inflammatory disease with complex genetic susceptibilities. Multi-ethnic genome-wide association studies have validated the association of sarcoidosis susceptibilities with single nucleotide variants on interleukin 23 receptor gene (IL23R), which is highly expressed in adrenal gland and testis, but not in skeletal muscle. Here we report concomitant ectopic expression of a canonical IL23R transcript and alternative polyadenylation of intron 6 of IL23R, leading to novel aberrant transcripts containing two retrotransposons, LINE1 (L1PA16) and THE1A, in the 3' untranslated region (IL23RL1-THE1A), in sarcoid myopathy (SM) compared with non-SM disease controls. RT-qPCR confirmed the expression of both transcripts in an additional sample set, including 14 SM and 29 non-SM. We also observed expression of both transcripts in T cells by single-nucleus RNA-sequencing. These findings should serve as an additional resource for investigating the role of IL23R transcript variants in the genetic background of sarcoidosis susceptibility and other inflammatory diseases.