Positron Emission Tomography in the Inflamed Cerebellum: Addressing Novel Targets among G Protein-Coupled Receptors and Immune Receptors

Decoding NLRP3 Inflammasome Activation in Alzheimer's Disease: A Focus on Receptor Dynamics

Alzheimer's disease (AD) is a leading neurodegenerative disorder marked by progressive cognitive decline and significant neuropsychiatric disturbances. Neuroinflammation, mediated by the NLRP3 inflammasome, is increasingly recognized as a critical factor in AD pathogenesis. The NLRP3 inflammasome, a crucial component of the innate immune system, is activated in response to both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). In AD, amyloid-beta (Aβ) plaques and tau aggregates act as DAMPs, triggering NLRP3 inflammasome activation in microglia and astrocytes. This activation leads to the production of pro-inflammatory cytokines IL-1β and IL-18, contributing to chronic neuroinflammation and neuronal death. This review explores the intricate mechanisms involved in NLRP3 activation, with a particular focus on TREM-2, Msn Kinase MINK, NF-κB, Toll-like receptors, and P2X7 receptors. Understanding these mechanisms offers insight into the multifaceted regulation of the NLRP3 inflammasome and its impact on AD pathology. By elucidating the roles of TREM-2, MINK1, NF-κB, TLRs, and P2X7 receptors, this review highlights potential therapeutic targets for modulating NLRP3 activity. Targeting these pathways could offer novel strategies for mitigating neuroinflammation and slowing the progression of AD. The interplay between these receptors and signaling pathways underscores the complexity of NLRP3 inflammasome regulation and its significance in AD, providing a foundation for future research aimed at developing effective therapeutic interventions.

TREM2 signaling in Parkinson's disease: Regulation of microglial function and α-synuclein pathology

BACKGROUND

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons, abnormal accumulation of α-synuclein (α-syn), and microglial activation. Triggering receptor expressed on myeloid cells 2 (TREM2) regulates multiple functions of microglia in the brain, and several studies have shown that TREM2 variant R47H is a risk factor for PD. However, the regulation of microglia by TREM2 in PD remains poorly understood.

METHODS

We constructed PD cell and animal models using α-syn preformed fibrils. siRNA knockdown and lentiviral overexpression were used to perturb TREM2 levels in cells, and TREM2 knockout mice and lentiviral overexpression was used in animal models to investigate the effects of TREM2 on microglial function, α-syn-related pathology, and dopaminergic neuron degeneration.

RESULTS

Microglia phagocytosed α-syn preformed fibrils in a concentration- and time-dependent manner, with some capacity to degrade α-syn aggregates. TREM2 expression increased in PD. In the context of PD, TREM2 knockout mice exhibited worsened pathological α-syn spread, decreased microglial reactivity, and increased loss of TH-positive neurons in the substantia nigra compared to wild-type mice. TREM2 overexpression enhanced reactive microglial aggregation towards the pathological site. Cellular experiments revealed that reduced TREM2 impaired microglial phagocytosis and proliferation, but enhanced autophagy via the PI3K/AKT/mTOR pathway.

CONCLUSION

TREM2 signaling in PD maintains microglial phagocytosis, proliferation, and reactivity, stabilizing autophagy and proliferation via the PI3K/AKT/mTOR pathway. Regulating TREM2 levels may be beneficial in PD treatment.

Targeting TREM2 for Parkinson's Disease: Where to Go?

Parkinson’s disease (PD) is one of most common neurodegenerative disorders caused by a combination of environmental and genetic risk factors. Currently, numerous population genetic studies have shown that polymorphisms in myeloid cell-triggered receptor II (TREM2) are associated with a variety of neurodegenerative disorders. Recently, TREM2 has been verified to represent a promising candidate gene for PD susceptibility and progression. For example, the expression of TREM2 was apparently increased in the prefrontal cortex of PD patients. Moreover, the rare missense mutations in TREM2 (rs75932628, p.R47H) was confirmed to be a risk factor of PD. In addition, overexpression of TREM2 reduced dopaminergic neurodegeneration in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine mouse model of PD. Due to the complex pathogenesis of PD, there is still no effective drug treatment. Thus, TREM2 has received increasing widespread attention as a potential therapeutic target. This review focused on the variation of TREM2 in PD and roles of TREM2 in PD pathogenesis, such as excessive-immune inflammatory response, α-Synuclein aggregation and oxidative stress, to further provide evidence for new immune-related biomarkers and therapies for PD.