*Purpose: CEACAM1 (CC1) is a transmembrane glycoprotein that undergoes extensive alternative splicing (AS) to generate CC1-S and CC1-L. It is currently unclear which of these two cytoplasmic isoforms is involved at the interface of immune liver injury and metabolic homeostasis.

*Methods: Murine studies used warm liver IRI (wIRI) for 6 h or 7 days to assess RNA splicing in CC1. Primary hepatocytes were cultured under hypoxia-reoxygenation (H/R) stress conditions to mimic liver wIRI. Antisense oligomer morpholinos, targeting CC1 exon 7, were used to induce “cytoprotective” hepatocyte CC1-S signaling under hypoxic conditions in hepatocyte cultures and orthotopic liver transplant (OLT) settings. Human liver biopsies were obtained 2 h after reperfusion and analyzed by qRT-PCR-assisted detection of CC1-S and HIF-1α.

*Results: Longitudinal CC1 AS mRNA isoform profiles were analyzed in a wIRI model. The peak of CC1-S occurred at 6 h (P<0.0009) and 7d (P<0.0007), reflecting combinatorial interactions at the CC1 variable exon 7. We addressed next how CC1 is regulated by oxidative stress by investigating the role of HIF-1α. Notably, in the presence of HIF-1α, under cold stimuli, CC1 responded to hepatocyte damage by dramatically upregulating its expression (P<0.001). This correlated with a decrease of p38 MAPK levels (P<0.001), a negative regulator of hepatic autophagy pathways. As proof-of-principle, wild-type mice treated with antisense morpholinos targeting CC1 exon 7 and subjected to warm IR-stress showed marked improvement of liver function, increased CC1-S in the liver, and spleen (P<0.0001). To clinically validate the murine findings, we retrospectively analyzed hepatic biopsies from fifty-five human OLT patients. We found a positive correlation between CC1 and HIF-1α levels in post-transplant donor liver biopsies (P<0.0128). Human OLTs divided into “low” (n=20) vs. “high” (n=20) CC1-S expression groups (n=40) showed high CC1-S levels were accompanied by improved pre-OLT hepatocellular function.

*Conclusions: This novel translational study identifies oxidative stress and hepatic tissue injury as catalytic drivers of CEACAM1 AS. The uncovered HIF-1α – CC1-S cytoprotective axis points toward its function in alleviating hepatic IRI and improving OLT survival/outcomes.

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