The ageing systemic milieu negatively regulates neurogenesis and cognitive function.

Regenerative capacity and cognitive function decline during ageing. A study using heterochronic parabiosis, in which pairs of young and old mice are surgically joined by a shared blood supply, shows that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in ageing mice. A proteomic screen identified a subset of plasma signalling proteins that correlate with the decreased neurogenesis observed in both normal ageing and parabiosis. CCL11 (also known as eotoxin) and 2-microglobulin factors classically involved in immune responses were among the identified factors able to decrease progenitor frequency and neural differentiation.