Figure 2. The role of the stem cell niche in stem cell performance (A) The young niche induces productive stem cell responses and, as a result, young tissues regenerate efficiently. (B) By contrast, the old niche inhibits stem cell responses. Rather than effective tissue regeneration, there is sustained inflammation and resulting fibrosis, perhaps further suppressing stem cell function and leading to apoptosis, senescence, or aberrant cell fate. (C) Promisingly, exogenous molecules that boost the regenerative responses of tissue stem cells, perhaps in part by rejuvenating the aged niche, promote effective repair of aged tissues, overriding the inhibitory influence of the old niches.