Can exosomes link the cellular and endocrine stress response? A test using the brown anole lizard ( <i>Anolis sagrei</i> ) as a model

Exosomes are nanoscale extracellular vesicles critical for intercellular communication, but their role in vertebrate stress responses remains unclear. We investigated exosome involvement in stress responses using brown anole lizards (<i>Anolis sagrei</i>), hypothesizing that acute stress would increase plasma exosome concentrations and inhibiting exosome secretion would attenuate the stress response. Using mixed-sex adult brown anoles (total <i>n</i> = 54 pairs), we conducted three experiments: a timed stress series, an adrenocorticotropic hormone (ACTH) challenge, and an exosome synthesis inhibitor (GW4869) challenge. Exosome concentrations were quantified using Nanoparticle Tracking Analysis and acetylcholinesterase (AChE) activity, while corticosterone levels were measured via enzyme-linked immunoassay (ELISA). Acute handling stress increased both plasma corticosterone and exosome concentrations, with a moderate significant correlation. ACTH injection elevated corticosterone but did not affect exosome levels. Blocking exosome synthesis with GW4869 significantly reduced corticosterone secretion, suggesting exosomes may play an indirect or concurrent role in stress regulation. This research provides the first <i>in vivo</i> evidence of exosomes' involvement in endocrine stress responses, offering a novel perspective on cellular stress signaling and potentially revealing an evolutionarily conserved mechanism of intercellular communication during stress adaptation.