Altered endoplasmic reticulum stress response in non-infectious neuronal cytoplasmic inclusions in the brain of an aged dog

Abstract

Eosinophilic neuronal cytoplasmic inclusions in dogs are typically associated with viral infections such as rabies (Negri bodies), but may also occur as age-related, incidental findings in humans and animals, including dogs. Here, we characterize non-infectious eosinophilic neuronal cytoplasmic inclusions resembling Negri bodies in the brain of a 15-year-old female Pinscher dog that presented with disorientation, circling to the left, instability, pedaling, hypersalivation, and episodic loss of consciousness. The dog was euthanized due to the severity of its neurologic signs. Histopathology and immunohistochemistry for a panel of neurodegenerative, stress, and infectious markers (glial fibrillary acid protein [GFAP], ionized calcium binding adaptor molecule 1 [IBA-1], neurofilament, glucose-regulated protein 78 [GRP78], glucose-regulated protein 94 [GRP94], inositol-requiring enzyme 1 [IRE1], X-box binding protein [XBP1], heat shock protein 70 (HSP70), ubiquitin, alpha B-crystallin [HSPB5], microtubule-associated protein 1 A/1B-light chain [LC3], p62/SQSTM1, and rabies virus) revealed eosinophilic neuronal inclusions that immunolabelled GRP78 and GRP94, which are endoplasmic reticulum chaperones mediators of the unfolded protein response. Transmission electron microscopy identified the inclusions as aggregates of finely-granular, electron-dense material composed of packed membranes. Neuronal cytoplasmic inclusions in this dog represent accumulations of proteins and activation of endoplasmic reticulum chaperones GRP78 and GRP94, suggesting a limited or ineffective unfolded protein response, but their association with neurologic signs needs further investigation.

Keywords: Aging; Endoplasmic reticulum stress; Glucose-regulated protein; Negri body; Neuronal inclusions.