Investigating the Pathological Relevance of N-acylsphingosine Amidohydrolase 2 (ASAH2) and Related Proteins in Alzheimer's Disease.

Background Alzheimer's disease (AD) is a progressive neurodegenerative disorder mainly characterized by progressive cognitive decline and memory loss. Identifying candidate biomarkers before the clinical onset of AD is crucial for enabling earlier diagnosis and timely therapeutic intervention. Among different molecular targets, N-acylsphingosine amidohydrolase 2 (ASAH2), a key enzyme in ceramide metabolism, has been linked to many neurodegenerative diseases, including AD. This study investigates ASAH2 expression in human serum and AD mouse models to explore its potential as an early biomarker and to understand its involvement in AD progression. Methods The protein levels in the serum of pre-AD, mild cognitive impairment, and control patients were measured using the SOMAscan assay platform (SomaLogic Inc., CO, USA) to identify potential candidate biomarkers for preclinical AD. ASAH2 expression at different Alzheimer's stages of triple transgenic (3x-TG) Alzheimer's mice organs and tissues was analyzed. Human serums and hepatoblastoma cells (also referred to as HepG2 cells) were stained and quantified with ASAH2, membrane, and vesicle trafficking proteins. Results We found that neutral ceramidase (ASAH2/ASAH2B) and sortilin-related VPS10 domain-containing receptor 2 (SORCS2) were significantly elevated in the serum of individuals who later developed Alzheimer's dementia. Similarly, 3x-TG AD mice showed an increased ASAH2 expression at three months, followed by a marked decline at 14 months compared to age-matched non-3x-TG controls. In non-3x-TG mice, ASAH2 was highly expressed in visceral organs such as the heart, liver, kidneys, lungs, and stomach, but was nearly absent in the brain. Ingenuity pathway analysis revealed dysregulation in lipid trafficking and inflammatory pathways. Additionally, we observed elevated lysosomal-associated membrane protein 1 (LAMP1) and reduced levels of filamin A and RAB7 (a member of the RAS oncogene family) in the pre-AD mild cognitive impairment group. Conclusion Our findings suggest that ASAH2 may play a significant role in the pathogenesis of AD, potentially contributing to early molecular changes that precede clinical symptoms. In addition, the identification of a subgroup of lipid- and membrane-associated proteins provides promising candidates for predictive biomarkers that could facilitate earlier diagnosis and offer new insights into the mechanisms underlying disease progression and possible therapeutic targets for AD prevention.