Inhibiting 15-PGDH blocks blood-brain barrier deterioration and protects mice from Alzheimer's disease and traumatic brain injury.

Alzheimer's disease (AD) and traumatic brain injury (TBI) are currently untreatable neurodegenerative disorders afflicting millions of people worldwide. These conditions are pathologically related, and TBI is one of the greatest risk factors for AD. Although blood-brain barrier (BBB) disruption drives progression of both AD and TBI, strategies to preserve BBB integrity have been hindered by lack of actionable targets. Here, we identify 15-hydroxyprostaglandin dehydrogenase (15-PGDH), an enzyme that catabolizes eicosanoids and other anti-inflammatory mediators, as a therapeutic candidate that protects the BBB. We demonstrate that 15-PGDH is enriched in BBB-associated myeloid cells and becomes markedly elevated in human and mouse models of AD and TBI, as well as aging, another major risk factor for AD. Pathological increase in 15-PGDH correlates with pronounced oxidative stress, neuroinflammation, and neurodegeneration, alongside profound BBB structural degeneration characterized by astrocytic endfeet swelling and functional impairment. Pharmacologic inhibition or genetic reduction of 15-PGDH in AD and TBI models strikingly mitigates oxidative damage, suppresses neuroinflammation, and restores BBB integrity. Most notably, inhibiting 15-PGDH not only halts neurodegeneration but also preserves cognitive function at levels indistinguishable from healthy controls. Remarkably, these neuroprotective effects in AD are achieved without affecting amyloid pathology, underscoring a noncanonical mechanism for treating AD. In a murine microglia cell line exposed to amyloid beta oligomer, major protection was demonstrated by multiple anti-inflammatory substrates that 15-PGDH degrades. Thus, our findings position 15-PGDH inhibition as a broad-spectrum strategy to protect the BBB and thereby preserve brain health and cognition in AD and TBI.