Evolutionarily conserved role of Telomerase reverse transcriptase (TERT) in programming the microenvironment via regulation of cGAS/STING pathway
Telomerase holoenzyme plays a critical role in maintaining telomere length, and thus in regulating inflammation caused by telomeric DNA damage. However, beyond its role in telomere maintenance, the molecular function of telomerase in directly regulating inflammation remains unclear. Here, we show that the reverse transcriptase component of telomerase, TERT, has a cell-type-specific role in directly regulating inflammation via the cytoplasmic cGAS-STING nucleic acid-sensing pathway. Analyses of murine and zebrafish models of gut inflammation and human colitis/Crohn's patients document that this function of TERT is evolutionarily conserved. Using our novel knock-in TERTVAA mouse model where reverse-transcriptase-inactive TERT is driven by its endogenous loci, and molecular, pharmacological and single-cell approaches we identify the myeloid subpopulation, termed T-MAC, wherein TERT enhances STING activation and initiates type-1 interferon responses independent of reverse transcriptase activity or telomere length. We highlight a hitherto unappreciated role of TERT in directly regulating inflammation and provide a therapeutic rationale for targeting TERT beyond cancers. Overall design: To understand the canonical and non-canonical role of TERT in programming the microenvironment, we have generated an enzymatically inactive TERT mouse model (TERT-VAA). Additionally, we utilized TERT WT and  TERT KO mouse models. We employed an experimental colitis model using Dextran Sulfate Sodium (DSS). Mice were treated with 3% DSS for 4 days, followed by 4 days of normal water. Colon tissues were harvested on day 8. RNA was isolated by Trizol and column purification. Bulk RNA Sequencing was performed for DSS untreated and treated mice of TERT WT, TERT VAA and TERT KO. The library was prepared using the Illumina Truseq Total RNA sequencing kit according to the manufacturer's guidelines. Paired-end sequencing was performed using Illumina Nextseq 2x76bp.