Loss of Homeostatic Microglia Signature in Prion Diseases

The Role of Glial Cells in Neurobiology and Prion Neuropathology

Prion diseases are rare and neurodegenerative diseases that are characterized by the misfolding and infectious spread of the prion protein in the brain, causing progressive and irreversible neuronal loss and associated clinical and behavioral manifestations in humans and animals, ultimately leading to death. The brain has a complex network of neurons and glial cells whose crosstalk is critical for function and homeostasis. Although it is established that prion infection of neurons is necessary for clinical disease to occur, debate remains in the field as to the role played by glial cells, namely astrocytes and microglia, and whether these cells are beneficial to the host or further accelerate disease. Here, we review the current literature assessing the complex morphologies of astrocytes and microglia, and the crosstalk between these two cell types, in the prion-infected brain.

Interactions between Cytokines and the Pathogenesis of Prion Diseases: Insights and Implications

Transmissible Spongiform Encephalopathies (TSEs), including prion diseases such as Bovine Spongiform Encephalopathy (Mad Cow Disease) and variant Creutzfeldt-Jakob Disease, pose unique challenges to the scientific and medical communities due to their infectious nature, neurodegenerative effects, and the absence of a cure. Central to the progression of TSEs is the conversion of the normal cellular prion protein (PrPC) into its infectious scrapie form (PrPSc), leading to neurodegeneration through a complex interplay involving the immune system. This review elucidates the current understanding of the immune response in prion diseases, emphasizing the dual role of the immune system in both propagating and mitigating the disease through mechanisms such as glial activation, cytokine release, and blood-brain barrier dynamics. We highlight the differential cytokine profiles associated with various prion strains and stages of disease, pointing towards the potential for cytokines as biomarkers and therapeutic targets. Immunomodulatory strategies are discussed as promising avenues for mitigating neuroinflammation and delaying disease progression. This comprehensive examination of the immune response in TSEs not only advances our understanding of these enigmatic diseases but also sheds light on broader neuroinflammatory processes, offering hope for future therapeutic interventions.

Host-microbe interactions at the blood-brain barrier through the lens of induced pluripotent stem cell-derived brain-like endothelial cells

Microbe-induced meningoencephalitis/meningitis is a life-threatening infection of the central nervous system (CNS) that occurs when pathogens are able to cross the blood-brain barrier (BBB) and gain access to the CNS. The BBB consists of highly specialized brain endothelial cells that exhibit specific properties to allow tight regulation of CNS homeostasis and prevent pathogen crossing. However, during meningoencephalitis/meningitis, the BBB fails to protect the CNS. Modeling the BBB remains a challenge due to the specialized characteristics of these cells. In this review, we cover the induced pluripotent stem cell-derived, brain-like endothelial cell model during host-pathogen interaction, highlighting the strengths and recent work on various pathogens known to interact with the BBB. As stem cell technologies are becoming more prominent, the stem cell-derived, brain-like endothelial cell model has been able to reveal new insights in vitro, which remain challenging with other in vitro cell-based models consisting of primary human brain endothelial cells and immortalized human brain endothelial cell lines.

Adipose-derived mesenchymal stromal cells decrease prion-induced glial inflammation in vitro

Prion diseases are characterized by the cellular prion protein, PrP^C, misfolding and aggregating into the infectious prion protein, PrP^Sc, which leads to neurodegeneration and death. An early sign of disease is inflammation in the brain and the shift of resting glial cells to reactive astrocytes and activated microglia. Few therapeutics target this stage of disease. Mesenchymal stromal cells produce anti-inflammatory molecules when exposed to inflammatory signals and damaged tissue. Here, we show that adipose-derived mesenchymal stromal cells (AdMSCs) migrate toward prion-infected brain homogenate and produce the anti-inflammatory molecules transforming growth factor β (TGFβ) and tumor necrosis factor-stimulated gene 6 (TSG-6). In an in vitro model of prion exposure of both primary mixed glia and BV2 microglial cell line, co-culturing with AdMSCs led to a significant decrease in inflammatory cytokine mRNA and markers of reactive astrocytes and activated microglia. This protection against in vitro prion-associated inflammatory responses is independent of PrP^Sc replication. These data support a role for AdMSCs as a beneficial therapeutic for decreasing the early onset of glial inflammation and reprogramming glial cells to a protective phenotype.