Clusterin: A Regulator of Glial Biology and Alzheimer’s Disease Pathogenesis

Alzheimer's disease (AD) is a chronic neurodegenerative condition and the leading cause of dementia globally, affecting around 50 million people. It is characterized by progressive memory and cognitive decline, and pathologically defined by extracellular β-amyloid (Aβ) plaques and intracellular hyper-phosphorylated tau (p-τ) in neurofibrillary tangles. Therapeutic efforts targeting Aβ and tau have yielded poor clinical results, raising questions about the suitability of these pathological features as drug targets. Microglia and astrocyte activation, first observed by Alois Alzheimer in 1907, have been reevaluated as potential contributors to AD progression rather than bystanders. Recent studies indicate that microglial dysfunction and neuroinflammation, likely play significant roles in AD pathogenesis. Clusterin (CLU), also known as apolipoprotein J, is the third most prominent risk gene associated with late-onset AD (LOAD). The precise role of CLU in the brain and in LOAD pathogenesis remains unclear. Multiple pieces of evidence have pointed to an immunomodulatory role of CLU in the peripheral organs; however, whether this role extends to the brain, particularly to the neuroinflammation mediating glial cells (microglia and astrocytes), remains unclear.This dissertation aimed to address this gap and examine the role of CLU in neuroinflammation. Chapter 1 provides an overview of AD and the role of neuroinflammation in driving the disease pathogenesis and delves deeply into the fundamental genetics and biology of CLU. In chapter 2, the role of CLU in microglial inflammation was investigated. The neuroinflammatory status was compared between wild-type (WT) and CLU-knockout (CLU-/-) mice. Loss of CLU was associated with a higher level of microglia activation and inflammation. Furthermore, using mouse primary cultures and a microglia cell line, the CLU expression profile was analyzed and compared to astrocytes, the major source of CLU in the brain. While astrocytes constitutively synthesized and secreted high levels of CLU, microglia were found to have very low levels of CLU expression, which, however, were significantly increased in response to stimulation by lipopolysaccharide (LPS). Functionally, loss of CLU led to a higher level of inflammation upon LPS stimulation, and treatment with recombinant mouse CLU protein attenuated the LPS-mediated microglia inflammatory status, suggesting that microglia increase their production of CLU to suppress neuroinflammation. In chapter 3, the role of CLU in regulating astrocytic activation was explored using primary astrocytes derived from WT and CLU-/- mice. Loss of CLU was associated with heightened astrocytic activation and morphological impairment. Moreover, a role of CLU in modulating astrocytic immunometabolism is supported since loss of CLU reduced ATP-induced intracellular calcium (Ca2+) response and the activity of a hydrolase enzyme, β-galactosidase. In chapter 4, the role of CLU in AD pathogenesis was investigated using an AD mouse model harboring AppNL-F/NL-F. Loss of CLU was found to impair cognitive functions, despite a notable reduction in Aβ deposition. To understand the mechanism behind these Aβ-independent cognitive effects mediated by CLU, single-nucleus RNA sequencing was performed. This analysis revealed a significant shift in brain neuronal composition upon CLU loss, characterized by a decrease in excitatory neurons and a concurrent increase in inhibitory neurons, impacting neurotransmission pathways.Overall, the findings from this dissertation highlight a significant role of CLU in regulating glial activation, neuroinflammation, and neurotransmission in AD pathogenesis, providing insights into why mutations in CLU are important genetic risk factors for LOAD.

Grantor dc:publisher

University of Kansas

Year dc:date.issued

2024

Author dc:creator

• Rawal, Punam

Advisor dc:contributor.advisor

• Zhao, Liqin

• Pharmacology
• Toxicology

Statement dc:rights

• Copyright held by the author.

Language dc:language.iso

en

Dc Identifier Other

http://dissertations.umi.com/ku:19454

OAI identifier oai:identifier

oai:kuscholarworks.ku.edu:1808/37469