Characterizing Heme Signaling and Bioavailability in Neurodegeneration

Abstract

Alzheimer’s disease is a neurodegenerative condition that results in cognitive decline, impacting over 40 million people worldwide. Alzheimer’s is characterized by amyloid beta plaques, tau tangles and neuroinflammation. Recently, neuroinflammation has emerged as a major player in disease progression, impacting astrocytes, microglia, and neurons. Prior work conducted in the Wood Lab suggests that the blood-derived factors heme and hemoglobin (Hb) modulate neuroinflammation, yet little work has been done to understand their effects on cell signaling. This study aims to expand on previous work analyzing heme interactions by determining the kinetics and bioavailability of heme using ratiometric heme sensors and studying inhibition of signaling pathways to determine modulation of heme signaling. Through experiments with ratiometric heme sensors, it can be determined if these changes in signaling are due to uptake of heme and intracellular interference of signaling pathways or if heme is externally interfering with these cells via extracellular mechanism. Results of these experiments show that astrocytes uptake heme, revealing that heme intracellular interactions may play a role in regulating downstream signaling. Furthermore, cell signaling experiments were conducted using primary mouse astrocytes and treatment with various inhibitors of the PI3K/Akt pathway. Results revealed that heme signaling is partially regulated by the mTOR pathway, as treatment with rapamycin, an mTOR inhibitor, resulted in decreased HO-1 expression. Understanding how heme is internalized by these cells and the mechanism of action, as well as which pathways modulate these effects will be useful for developing future heme-based therapies.