Stromal FGF21 Preserves Aged Thymus

Researchers asked whether they could slow age-related shrinkage of the thymus, the organ that makes new T cells, in 24-month-old mice. They raised fibroblast growth factor 21 (FGF21), a metabolic hormone, in liver cells for blood circulation or locally in thymic epithelial cells, the support cells inside the thymus. A fivefold rise in circulating FGF21 left thymus size, cell number and developing T cells unchanged. Local FGF21 preserved the cortex, medulla and their boundary, increased cellularity, and reduced lipid-filled fibroadipogenic cells, stromal cells that accumulate fat. Deleting beta-klotho, the FGF21 co-receptor on thymic epithelial cells, accelerated thymic aging. Where FGF21 was made determined whether the aged thymus retained its T-cell-making structure.