Restoration of aged liver regeneration by youthful systemic factors via LTβ-driven hepatocyte reprogramming.

BACKGROUND & AIMS: The regenerative capacity of the liver decreases with age, limiting surgical options for elderly patients. While youthful systemic factors can reverse liver aging, the underlying mediators remain unclear. This study aimed to investigate the systemic factors and cellular mechanisms that promote aged liver regeneration.

METHODS

We retrospectively analyzed a split liver transplantation (SLT) cohort (n=36 pairs) to evaluate human graft regeneration. In animal models, 18-month-old and 2-month-old mice were subjected to heterochronic parabiosis, a procedure in which two animals of different ages were surgically connected to share a common circulation, followed by 70% partial hepatectomy. Single-cell transcriptomic profiling and lineage tracing were used to map hepatocyte dynamics. To elucidate the underlying mechanisms, hepatocyte-specific lymphotoxin β receptor (Ltbr) knockout and in vivo B-cell manipulations were employed to validate the key effectors and downstream signaling.

RESULTS

In the SLT cohort, grafts in young recipients exhibited a significantly higher liver regeneration ratio than those in aged recipients. In murine experiments, heterochronic parabiosis significantly accelerated regeneration in aged mice. Single-cell transcriptomic profiling and lineage-tracing analyses revealed that aged periportal hepatocytes underwent transient somatic reprogramming to aid hepatocyte repopulation. Mechanistically, we discovered that this reprogramming was driven by young parabiont-derived lymphotoxin β (LTβ)/LTBR signaling. Further analysis identified young B cells as critical effectors, as these cells exhibited increased liver infiltration and elevated LTβ expression to promote hepatocyte reprogramming. Moreover, agonistic LTBR antibody administration successfully induced periportal reprogramming and accelerated aged liver regeneration.

CONCLUSIONS

Young B-cell-derived LTβ promotes aged liver regeneration by promoting the transient somatic reprogramming of periportal hepatocytes via LTβ/LTBR signaling. Our study highlights the therapeutic potential of LTβ-based strategies to increase regeneration in aging populations.

IMPACT AND IMPLICATIONS: The regenerative capacity of the liver decreases with age, limiting the utilization of elderly grafts. This study demonstrates that youthful systemic circulation rejuvenates aged liver regeneration through young B-cell-derived lymphotoxin β (LTβ), which induces the transient somatic reprogramming of periportal hepatocytes via LTβ/LTBR signaling. These findings are highly relevant to transplant surgeons, hepatologists, and aging researchers. Practically, short-term pharmacological LTBR agonism could be utilized by clinicians to therapeutically "pre-condition" elderly donor livers or enhance post-hepatectomy regeneration in older patients. Furthermore, our work establishes heterochronic transplantation as a powerful clinical research platform to investigate anti-aging mechanisms and rejuvenation strategies across solid organs.