Prostaglandin J2 (PGJ2) is a metabolite of PGD2 and an agonist of the prostaglandin D2 (PGD2) receptor subtypes DP1 and DP2/CRTH.^1,2 It is formed from PGD2 by spontaneous dehydration.³ PGJ2 binds to DP1 and DP2/CRTH receptors (Kis = 0.9 and 6.6 nM, respectively) and either increases or inhibits the production of cAMP (EC50s = 1.2 and 13.1 nM, respectively, in HEK293 cells expressing the human receptors).^1,2 PGJ2 is neurotoxic and induces apoptosis, oxidative stress, and the accumulation of ubiquitinated proteins in the brain.⁴ It promotes the cleavage of amyloid precursor protein (APP) by α- and β-secretase in primary rat cerebral cortical neurons when used at a concentration of 10 µM.³ The levels of PGJ2 increase in the brain after stroke or traumatic brain injury (TBI) in rodents and it accumulates in the spinal cord of patients with sporadic amyotrophic lateral sclerosis (ALS).