PF4 and Cognitive impairment: In addition, exercise can induce hippocampal precursor cell proliferation in aged mice by activating platelets, that is, increasing the systemic levels of the platelet-derived exerkine CXCL4/platelet factor 4 (PF4) ameliorates age-related regenerative and cognitive impairments in a hippocampal neurogenesis-dependent manner [250].