Modulation of hippocampal protein expression by a brain penetrant biologic TNF‐α inhibitor in the 3xTg Alzheimer’s disease mice

Abstract Background Alzheimer’s disease (AD) is a chronic neuroinflammatory condition and the proinflammatory cytokine, tumor necrosis factor alpha (TNF‐α), is a key mediator of neuroinflammation in AD. Biologic TNF‐α inhibitors (bTNFIs) can block cerebral TNF‐α if these large molecules cross the blood‐brain barrier (BBB). Thus, a model bTNFI, the extracellular domain of type II TNF‐α receptor (TNFR) which can bind to and sequester TNF‐α, has been reengineered to enable brain delivery by fusion with a mouse transferrin receptor antibody (TfRMAb). TfRMAb binds to the BBB TfR to deliver the TNFR into the brain via receptor‐mediated transcytosis. Previously, we found the TfRMAb‐TNFR to be protective in a mouse model of amyloidosis (APP/PS1) and tauopathy (PS19), and the aim of the current study was to investigate its effects in a mouse model that combines both amyloidosis and tauopathy (3xTg‐AD mice). Method Eight‐month‐old female triple transgenic 3xTg‐AD mice were injected intraperitoneally with saline (n = 11) or TfRMAb‐TNFR (3 mg/kg; n = 11) three days per week for 12 weeks. At the end of treatment, brains were processed for hippocampal immunohistochemistry and high‐resolution multiplex NanoString spatial proteomics using the GeoMx protein assays for neuroscience. Result TfRMAb‐TNFR treatment significantly reduced mature β‐sheet rich Aβ plaques and increased plaque‐associated microglial localization around larger plaques in the 3xTg mice. Further, TfRMAb‐TNFR increased plaque‐associated microglial TREM2 compared with saline‐treated 3xTg mice. From a total of 64 target proteins studied using spatial proteomics (comparing protein expression in the Aβ‐plaque bearing vs. plaque‐free regions), 39 (61%) differentially expressed proteins (DEP) were identified in the 11‐month‐old 3xTg mice, comprising of proteins related to neurodegeneration (10% of DEP), neuroinflammation (41% of DEP), amyloid (21% of DEP) and tau (10% of DEP) pathology, autophagy (10% of DEP) and other pathways (8% of DEP). TfRMAb‐TNFR treatment modulated proteins involved in Aβ clearance and processing, microglial function, RNA processing, and neurodegeneration. Majority of these proteins were relevant to microglial function (∼ 40%). Conclusion The study highlights that TfRMAb‐TNFR modulates several proteins involved in AD pathology and progression and largely suggests a microglia‐centric mechanism of action of this treatment in the 3xTg mice.