Mutations in healthy tissues: a double-edged sword for tissues homeostasis

Healthy tissues become progressively populated of clonally expanded cells that have acquired somatic mutations. Often these mutations modify cancer genes promoting cell plasticity, self-renewal, and growth, all features known to decline with ageing. Despite being pervasive across tissues and persistent throughout life, only rarely mutant cells become pathogenic. Here we hypothesise that somatic mutations enhance tissue integrity by increasing the fitness of stem/progenitor cells (SPCs) to counterbalance their age-induced decline. Increased SPC fitness at the cellular level increases the fitness at the tissue level, thus preserving the overall tissue regenerative potential. To test this hypothesis, we propose to investigate the effect of somatic mutations on SPC fitness in solid tissues and blood using complementary and synergistic approaches specific to our teams, bridging the historically distinct fields of evolutionary genetics and stem cell biology. Through the analysis of human tissues and the use of complex mouse models, we will dissect the interactions between mutant SPCs and their niche, at homeostasis and upon insults. We will determine whether the expansion of mutant SPCs over time leads to a progressive decline in SPC diversity, which eventually increases disease risk. We will adopt a progressive approach. We will first characterise the mutant clone (WP1) and its crosstalk with the niche (WP2) at homeostasis. We will then test the response of mutant clone and niche to physiological (WP3) and pathological (WP4) challenges. We will finally assess the occurrence of a multiorgan crosstalk conveyed by mutant blood on mutant solid tissues (WP5). This study will radically transform our understanding of tissue homeostasis and clarify the relationship between somatic mutations, ageing and disease. A deeper knowledge of the mechanisms that maintain the homeostatic equilibrium over time is the first step to guide intervention and disease prevention.