Alteration of Gene Expression and Protein Solubility of the PI5-Phosphatase SHIP2 are Correlated with Alzheimer’s Disease Pathology Progression

Neurology Biochemistry Genetics Basic Medical Sciences Life Sciences Immunology Medicine Cell Biology
Alzheimer’s Disease SHIP2 INPPL1 EGFR Tau Amyloid β GWAS CSF pTau

Changes in Gene Expression and Protein Insolubility in Alzheimer’s Disease Progression

Background Introduction

As the most common type of dementia, Alzheimer’s Disease (AD) is well-known for its two main neuropathological features: amyloid plaques and neurofibrillary tangles (NFTs). Amyloid plaques consist of β-amyloid (Aβ) peptide segments generated from sequential cleavage of amyloid precursor protein (APP); neurofibrillary tangles, on the other hand, are mainly composed of hyperphosphorylated paired helical filaments (PHFs)-tau protein. NFTs appear not only in Alzheimer’s Disease but also in other tauopathies such as Frontotemporal Dementia (FTD-tau), Corticobasal Degeneration (CBD), and Progressive Supranuclear Palsy (PSP).

Recent network studies have identified that upregulation of transcription levels of SHIP2 (SH2 domain-containing inositol 5-phosphatase 2, encoded by the INPPL1 gene) is significantly associated with cognitive decline and pathological changes in human AD and aging brains. Through its dephosphorylating activity, SHIP2 regulates the generation of PI(3,4)P2 from PI(3,4,5)P3 and is involved in various human diseases such as metabolic syndrome, diabetes, and breast cancer. Systematic regulation of phosphoinositides is particularly critical in AD, and SHIP2 inhibitors are seen as potential novel therapeutic targets. However, research on its expression and localization changes during the course of Alzheimer’s Disease is relatively limited.

Research Sources

The original article of this report is titled “Alteration of gene expression and protein solubility of the PI 5-Phosphatase SHIP2 are correlated with Alzheimer’s disease pathology progression,” authored by Kunie Ando et al., published in the journal Acta Neuropathologica (2024, Volume 147, Page 94). The authors are from institutions such as the Université Libre de Bruxelles (ULB), VIB Center for Molecular Neurology, University of Antwerp (UAntwerpen), and Hôpital de la Pitié-Salpêtrière. The research was supported by brain bank samples from various institutions in France and Belgium and funded by agencies such as the Belgian National Fund for Scientific Research (FNRS).

Research Process

Research Design and Methods

  1. Sample Collection and Processing:

    • Brain tissue samples were obtained from the frontal cortex (T1 isocortex) of AD patients and non-demented control individuals. The samples were subjected to graded extraction using standard RIPA and Sarkosyl buffers to obtain soluble and insoluble protein samples, respectively.

  2. Gene Expression Analysis:

    • RNA-seq data analysis of the Mayo Clinic cohort focused on the mRNA levels of EGFR and INPPL1, especially their changes during Braak stages 0-vi.

  3. Protein Level Detection:

    • Western blot (WB) analysis was used to detect the levels of soluble and insoluble proteins in the extracted samples. The expression levels of SHIP2 and EGFR in different graded samples were assessed using various antibodies, such as anti-SHIP2, anti-Aβ42, and anti-GAPDH.

  4. Immunohistochemistry and Immunofluorescence:

    • Double immunofluorescence labeling of SHIP2 with Aβ and phosphorylated tau (p-tau) was performed on brain tissue sections. Microscopic observation was used to determine the localization and distribution of SHIP2 in brain regions with or without pathological burden.

  5. Genetic Association Analysis:

    • Using a large amount of genome-wide association study (GWAS) data, the association between genetic variations in INPPL1 and AD risk, as well as AD-related cerebrospinal fluid (CSF) biomarkers such as p-tau levels, was analyzed.

Main Results

  1. Gene Expression Changes:

    • In the Mayo Clinic cohort, normalized gene expression levels of EGFR and INPPL1 were significantly upregulated in AD brain samples.

  2. Protein Levels and Distribution:

    • Although the overall brain protein levels of SHIP2 did not show significant differences between AD samples and controls, its level in the RIPA-insoluble fraction was significantly increased, suggesting mislocalization to the insoluble protein aggregates. The distribution of EGFR showed a similar trend, especially correlated with p-tau levels during pathological progression.

  3. Changes in Immunoreactivity:

    • Immunohistochemical results showed that SHIP2 immunoreactivity increased markedly with disease progression, particularly in astrocytes and degenerating neurites associated with amyloid plaques. This increase in SHIP2 was also observed in other neurodegenerative diseases with amyloid pathology such as DS/AD, CAA, and AD with LB, but not in primary tauopathies like PSP and CBD.

  4. Transgenic Mouse Model Validation:

    • Analysis of Alzheimer’s disease transgenic mouse models (such as 5XFAD and TG30) further confirmed the mechanism of SHIP2 insoluble protein reaction in mouse models, especially in the highly amyloidogenic 5XFAD mouse brain.

  5. Association of Genetic Variants with Biomarkers:

    • The INPPL1 locus variant rs11235459 was significantly associated with decreased INPPL1 gene expression in the brain and reduced CSF p-tau levels, suggesting this variant might regulate INPPL1 expression and consequently impact tau pathology in AD progression.

Research Conclusions and Significance

This study demonstrates that SHIP2 is not only upregulated at the gene expression level during AD progression but also exhibits significant RIPA-insoluble changes in AD brains. These changes are closely related to amyloid pathology, suggesting a key role of SHIP2 in linking amyloid and tau pathologies in Alzheimer’s Disease. Additionally, this research is the first to reveal the potential impact of INPPL1 gene locus variants on brain SHIP2 expression and CSF p-tau levels. Given SHIP2’s role in various human diseases, SHIP2 might not only serve as a therapeutic target for Alzheimer’s Disease but also as a novel biomarker for pathological progression, offering significant scientific research and clinical application value.

Research Highlights

  1. This study systematically investigated SHIP2 changes at the gene expression, protein level, and its localization and distribution in cells in AD samples for the first time.
  2. The main innovation is the proposal of SHIP2 as a core regulator in the EGFR signaling pathway, connecting amyloid and tau pathologies in Alzheimer’s Disease.
  3. By combining various cutting-edge experimental methods with large-scale genetic analysis, the study detailed the role of SHIP2 in Alzheimer’s Disease progression mechanisms.

Through this research, we have gained a deeper understanding of protein dynamics and their genetic regulatory mechanisms in Alzheimer’s Disease progression, providing a scientific basis for future pathological interventions targeting SHIP2.