Disruption of Lysosomal Homeostasis Following Combined Exposure to Lead and Amyloid‐β Peptides (25–35) and (1–40) in SH‐SY5Y Cells

Environmental exposure to heavy metals, specifically to lead (Pb), remains a significant global health concern, as accumulating evidence identifies it as a potent neurotoxicant capable of disrupting neuronal homeostasis. Similarly, endogenous amyloid‐β peptides (Aβps) are recognized as neurotoxic species that impair neuronal proteostasis, thereby sensitizing neurons to environmental stressors. Given that neuronal survival critically depends on intact lysosomal homeostasis, the impairment of lysosomal acidification and structural integrity may serve as a key driver for neuronal loss. In this study, we utilized human SH‐SY5Y cells to elucidate the mechanisms by which Pb and Aβp (25–35) + Aβp (1–40), both individually and in combination, disrupt lysosomal homeostasis. Our results demonstrate that while individual exposures induce moderate stress, the comprehensive co‐exposure to Pb + Aβp (25–35) + Aβp (1–40) triggers a profound loss of lysosomal homeostasis. This is characterized by a marked impairment of lysosomal acidification, alterations in LysoTracker‐positive acidic vesicular compartments and increased lysosomal membrane permeabilization. Furthermore, co‐exposure also disrupts lysosomal Ca 2+ homeostasis and downregulates the TFEB‐mediated CLEAR gene network, including TRPML1, LAMP1, LAMP2 and Cathepsin B at both the transcriptional and translational levels. Collectively, these findings demonstrate that the combined treatment of Pb + Aβp (25–35) + Aβp (1–40) triggers a multifaceted failure of the lysosomal system. This further suggests that the failure of cellular adaptive responses induced by environmental neurotoxicants like Pb exhausts the functional reserve of neurons, sensitizing them to endogenous pathological insults and ultimately driving the progression of neurodegenerative disorders.