Sentinel cells in the basement membrane form a reparative niche in the lung.

We engineered an ultrasensitive reporter of , a biomarker of cellular senescence. Our reporter detected -expressing fibroblasts with certain senescent characteristics that appeared shortly after birth in the basement membrane adjacent to epithelial stem cells in the lung. Furthermore, these fibroblasts had enhanced capacity to sense tissue inflammation and respond through their increased secretory capacity to promote epithelial regeneration. In addition, expression was required in fibroblasts to enhance epithelial regeneration. This study highlights a role for fibroblasts as tissue-resident sentinels in the stem cell niche that monitor barrier integrity and rapidly respond to inflammation to promote tissue regeneration.