Microglial Activation in the Pathogenesis of Huntington's Disease
Hui-Ming Yang1, Su Yang2, Shan-Shan Huang3
1Department of Neurology, Xiangya Hospital, Central South UniversityChangsha, China.
Insights
Huntington's disease (HD) involves mutant huntingtin protein accumulation in microglia, impacting neurodegeneration. This review focuses on M1 and M2 microglial activation states and their roles in HD pathogenesis.
Area of Science:
- Neuroscience
- Immunology
- Genetics
Background:
- Huntington's disease (HD) is an inherited neurodegenerative disorder caused by CAG trinucleotide repeats in the HTT gene.
- Mutant huntingtin accumulation in microglia contributes to neurodegeneration in HD via cell-autonomous and non-cell-autonomous mechanisms.
- Microglia, the CNS immune cells, exhibit M1 (pro-inflammatory) and M2 (anti-inflammatory/growth factor) activation phenotypes.
Purpose of the Study:
- To review the current understanding of microglial activation in Huntington's disease pathogenesis.
- To focus on the roles of M1 and M2 microglial phenotypes in HD progression.
- To summarize the signaling pathways associated with microglial activation in HD.
Main Methods:
- Literature review of studies on Huntington's disease and microglial activation.
- Analysis of research on M1 and M2 microglial phenotypes and their functions.
- Examination of signaling pathways involved in microglial responses in the CNS.
Main Results:
- Aberrant mutant huntingtin in microglia plays a critical role in HD neurodegeneration.
- Microglial activation can be neurotoxic (M1) or neuroprotective (M2).
- Specific cytokines and growth factors are released by M1 and M2 microglia, influencing HD progression.
Conclusions:
- Microglial activation, particularly the balance between M1 and M2 phenotypes, is central to Huntington's disease pathogenesis.
- Understanding these microglial pathways is crucial for developing therapeutic strategies for HD.
- Further research into microglial signaling in HD could reveal novel targets for intervention.
Abstract:
Huntington's disease (HD) is an autosomal dominantly inherited neurodegenerative disorder caused by expanded CAG trinucleotide repeats (>36) in exon 1 of HTT gene that encodes huntingtin protein. Although HD is characterized by a predominant loss of neurons in the striatum and cortex, previous studies point to a critical role of aberrant accumulation of mutant huntingtin in microglia that contributes to the progressive neurodegeneration in HD, through both cell-autonomous and non-cell-autonomous mechanisms. Microglia are resident immune cells in the central nervous system (CNS), which function to surveil the microenvironment at a quiescent state. In response to various pro-inflammatory stimuli, microglia become activated and undergo two separate phases (M1 and M2 phenotype), which release pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), anti-inflammatory cytokines, and growth factors (TGF-β, CD206, and Arg1), respectively. Immunoregulation by microglial activation could be either neurotoxic or neuroprotective. In this review, we summarized current understanding about microglial activation in the pathogenesis and progression of HD, with a primary focus of M1 and M2 phenotype of activated microglia and their corresponding signaling pathways.
