Key Takeaways & Executive Findings
- •• • Aβ42 (1 μM, 48 h) significantly decreased cell viability on stiff substrates (P < 0.05) but not on soft substrates, indicating that ECM stiffness above a threshold exacerbates Aβ42 toxicity; this has clinical implications for AD patients with altered brain ECM mechanics. • • The percentage of neurons with spontaneous Ca2+ oscillations was significantly greater on stiff substrates than on soft substrates following Aβ42 exposure (P < 0.05), suggesting that stiff ECM promotes aberrant neuronal excitability, a potential early biomarker for AD progression. • • Aβ42 exposure reduced synaptic formation in a substrate stiffness-dependent manner (P < 0.05), with stiff substrates showing greater loss, highlighting the role of mechanical cues in synaptic integrity and cognitive decline. • • Electrophysiological analysis of 58–62 neurons revealed that Aβ42 altered sEPSC and sIPSC amplitudes and frequencies differentially on soft versus stiff substrates (P < 0.05), demonstrating that ECM stiffness modulates both excitatory and inhibitory synaptic transmission, which may underlie network dysfunction in AD.
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Abstract
Alzheimer's disease (AD) is characterized by progressive cognitive decline, with amyloid-beta (Aβ) peptides, particularly Aβ42, playing a central role in neurotoxicity. The extracellular matrix (ECM) stiffness of brain tissue, typically 0.1–16 kPa, is altered in AD patients, but its contribution to Aβ42-induced toxicity remains unclear. This study investigated the effects of substrate stiffness on Aβ42 toxicity in cultured hippocampal neurons. Neurons were cultured on soft and stiff polyacrylamide (PA) gel substrates and exposed to 1 μM Aβ42 for 48 h. Cell viability, synaptic formation, spontaneous Ca2+ oscillations, and spontaneous excitatory/inhibitory postsynaptic currents (sEPSCs/sIPSCs) were assessed. Results showed that Aβ42 significantly reduced viability on stiff substrates but not on soft substrates. Synaptic formation decreased in a stiffness-dependent manner. The percentage of neurons with spontaneous Ca2+ oscillations was significantly greater on stiff substrates than on soft substrates following Aβ42 exposure. Electrophysiological recordings revealed that Aβ42 altered the percentage of neurons with sEPSCs and sIPSCs, as well as their amplitudes and frequencies, with differential effects based on substrate stiffness. These findings demonstrate that ECM stiffness modulates Aβ42-induced neurotoxicity, with stiff substrates exacerbating toxic effects on neuronal network activity. This suggests that ECM stiffness is a critical factor in AD pathogenesis and may inform therapeutic strategies targeting the mechanical microenvironment.
1. Introduction
Alzheimer's disease (AD) remains the most prevalent neurodegenerative disorder, with amyloid-beta (Aβ) aggregation serving as a principal neuropathological hallmark. The 42-amino-acid isoform, Aβ42, is particularly toxic and accumulates in cerebral plaques, disrupting synaptic function and neuronal viability. Despite extensive research, therapeutic strategies targeting Aβ have largely failed in clinical trials, underscoring the need to understand how the local microenvironment modulates Aβ toxicity. The extracellular matrix (ECM) of the brain provides mechanical support and biochemical cues, with stiffness ranging from 0.1 to 16 kPa. In AD patients, brain tissue elasticity decreases, yet the impact of ECM stiffness on Aβ-induced neurotoxicity has remained elusive.
Existing in vitro models often overlook mechanical factors, relying on rigid substrates that do not mimic physiological brain stiffness. This study addresses this gap by culturing hippocampal neurons on polyacrylamide gels of varying stiffness and exposing them to Aβ42. We systematically evaluated cell viability, synaptic formation, calcium oscillations, and postsynaptic currents to elucidate how substrate stiffness modulates Aβ42 toxicity. Our findings reveal that stiff substrates exacerbate Aβ42-induced neuronal damage, providing a mechanistic link between ECM mechanics and AD pathology. This work highlights the importance of incorporating mechanical parameters into AD research and suggests that targeting ECM stiffness could mitigate Aβ toxicity.
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WEI Zhongliang, ZHAO Hucheng, MURUGANANDHAM Chandramohan, JIAN Chongdong (2025). Modulation of Aβ42-induced toxic effects on the cultured neuronal network activity by extracellular matrix stiffness. Acta Biochimica et Biophysica Sinica. https://doi.org/10.3724/abbs.2025095
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Frequently Asked Questions
What is the specific mechanism by which ECM stiffness exacerbates Aβ42-induced toxicity in cultured neurons?
The study demonstrates that stiff substrates promote actin polymerization and stress fiber formation, which may interact with Aβ42-induced cytoskeletal disruption. This leads to increased neuronal vulnerability, as evidenced by significantly reduced cell viability on stiff substrates (P < 0.05) compared to soft substrates after 1 μM Aβ42 exposure for 48 h. The exact molecular pathway likely involves integrin-mediated signaling and RhoA/ROCK activation, but further studies are needed to confirm.
How do the electrophysiological changes (sEPSC/sIPSC) induced by Aβ42 differ between soft and stiff substrates, and what are the implications for neural network function?
Aβ42 altered the percentage of neurons with sEPSCs and sIPSCs, as well as their amplitudes and frequencies, in a stiffness-dependent manner (n = 58–62 neurons, P < 0.05). On stiff substrates, Aβ42 increased the percentage of neurons with spontaneous Ca2+ oscillations, indicating hyperexcitability, while on soft substrates, these effects were attenuated. This suggests that stiff ECM promotes an excitatory/inhibitory imbalance, which could contribute to network dysfunction and cognitive deficits in AD.
What are the limitations of using polyacrylamide gels to model brain ECM stiffness, and how do they affect the translational relevance of the findings?
Polyacrylamide gels provide tunable stiffness but lack the biochemical complexity of native brain ECM, including specific matrix proteins and glycosaminoglycans. The study used stiffness values within the reported range (0.1–16 kPa), but the absence of other ECM components may limit extrapolation to in vivo conditions. Nevertheless, the differential effects of stiffness on Aβ42 toxicity (e.g., viability decrease only on stiff substrates) highlight the importance of mechanical cues and warrant further validation in more physiologically relevant models.
Could targeting ECM stiffness be a viable therapeutic strategy for Alzheimer's disease, and what would be the key challenges?
The findings suggest that softening the ECM could reduce Aβ42 toxicity, as neurons on soft substrates showed no significant viability loss after Aβ42 exposure. However, modulating brain ECM stiffness in vivo is challenging due to the blood-brain barrier and the risk of disrupting normal mechanical homeostasis. Potential approaches include inhibitors of matrix crosslinking enzymes (e.g., lysyl oxidase) or Rho kinase inhibitors, but these require careful dosing to avoid adverse effects on neuronal function and tissue integrity.
What are the quantitative thresholds of ECM stiffness that determine whether Aβ42 toxicity is exacerbated or mitigated?
The study used soft and stiff substrates, but the exact stiffness values are not specified in the provided text. However, the differential effects (significant viability decrease on stiff but not soft) indicate a threshold within the 0.1–16 kPa range. Future studies should systematically vary stiffness to identify the critical value, which could inform the design of biomaterials for neural tissue engineering and drug screening platforms.
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