Journal Article

Neuronal cathepsin S increases neuroinflammation and causes cognitive decline via CX3CL1‐CX3CR1 axis and JAK2‐STAT3 pathway in aging and Alzheimer's disease

Ren, Ming‐Jing, Shi, Xiao‐Qing, Liu, Pei‐Pei, Li, Ming‐Li, Ren, Kai‐Di, Huang, Bing, Yang, Yang, Cheng, Meng, Yin, Fan‐Xiang, Wang, Dian‐Dian, Guo, Yan‐Hong, Liu, Xiao‐Hui, Li, Shu‐Ang, Wu, Yue, Xin, Yong‐Juan, Kang, Jian‐Sheng, Liu, Xiao‐Tong, Yang, Run‐Zhou

2025

Overview

Aging is an intricate process involving interactions among multiple factors, which is one of the main risks for chronic diseases, including Alzheimer's disease (AD). As a member of cysteine protease, cathepsin S (CTSS) has been implicated in inflammation across various diseases. Here, we investigated the role of neuronal CTSS in aging and AD started by examining CTSS expression in hippocampus neurons of aging mice and identified a significant increase, which was negatively correlated with recognition abilities. Concurrently, we observed an elevation of CTSS concentration in the serum of elderly people. Transcriptome and fluorescence‐activated cell sorting (FACS) results revealed that CTSS overexpression in neurons aggravated brain inflammatory milieu with microglia activation to M1 pro‐inflammatory phenotype, activation of chemokine C‐X3‐C‐motif ligand 1 (CX3CL1)—chemokine C‐X3‐C‐motif receptor 1 (CX3CR1) axis and janus kinase 2 (JAK2)—signal transducer and activator of transcription 3 (STAT3) pathway. As CX3CL1 is secreted by neurons and acts on the CX3CR1 in microglia, our results revealed for the first time the role of neuron CTSS in neuron–microglia “crosstalk.” Besides, we observed elevated CTSS expression in multiple brain regions of AD patients, including the hippocampus. Utilizing CTSS selective inhibitor, LY3000328, rescued AD‐related pathological features in APP/PS1 mice. We further noticed that neuronal CTSS overexpression increased cathepsin B (CTSB) activity, but decreased cathepsin L (CTSL) activity in microglia. Overall, we provide evidence that CTSS can be used as an aging biomarker and plays regulatory roles through modulating neuroinflammation and recognition in aging and AD process. Showing the roles of neuronal CTSS in the process of aging and Alzheimer's disease (AD). As a cysteine protease cathepsin family member, CTSS degrades proteins along the endocytic pathway in young and healthy mice. In aging and AD model mice, the expression level of neuronal CTSS is significantly elevated in neurons, which increases neuroinflammation and causes cognitive decline via CX3CL1‐CX3CR1 axis and JAK2‐STAT3 pathway. LY 3000328, the selective inhibitor of CTSS, LY3000328, significantly rescues AD‐related pathological features in APP/PS1 mice.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc
• Subject: Adult / Aged / Aging / Aging - metabolism / Alzheimer Disease - etiology / Alzheimer Disease - metabolism / Alzheimer Disease - prevention & control / Alzheimer's disease / Amyotrophic lateral sclerosis / Animals / Benzopyrans / Biomarkers - metabolism / Carbamates / Cathepsin B / Cathepsin L / Cathepsin S / Cathepsins - antagonists & inhibitors / Cathepsins - metabolism / Cell activation / Chemokine CX3CL1 - metabolism / Chemokines / Cognitive ability / CX3C Chemokine Receptor 1 - metabolism / CX3CR1 protein / Cysteine proteinase / Female / Flow cytometry / Geriatrics / Hippocampus / Hippocampus - enzymology / Humans / Huntingtons disease / Inflammation / Janus kinase / Janus Kinase 2 / Male / Memory - physiology / Mice / Mice, Inbred C57BL / Mice, Transgenic / Microglia / Microglia - enzymology / Middle Aged / Morris Water Maze Test / neurodegenerative disease / Neurodegenerative diseases / neuroinflammation / Neuroinflammatory Diseases - etiology / Neuroinflammatory Diseases - metabolism / Neurons / Neurons - enzymology / Open Field Test / Parkinson's disease / Phenotypes / Presenilin 1 / Primary Cell Culture / recognition / Signal Transduction / Stat3 protein / STAT3 Transcription Factor / Transcriptomes / Tumor necrosis factor-TNF / Up-Regulation