Sorensen, G. | bioRxiv Science

bioRxiv2026

Mitochondrial protein import couples proteostasis failure to mitochondrial permeabilization

Proteostasis failure is a hallmark of stress and disease, yet how it compromises mitochondrial integrity remains unclear. Here, we identify mitochondrial protein import as a critical pathway linking proteostasis failure to mitochondrial injury. We show that Raptinal, previously characterized as a rapid inducer of apoptosis, impairs the folding of newly synthesized proteins rather than directly disrupting mitochondrial membranes. The resulting proteotoxic stress drives mitochondrial outer membrane permeabilization and intrinsic apoptosis independently of BCL-2 family pore-forming proteins. VBIT4, a compound commonly used to maintain mitochondrial integrity, inhibited this pathway, and chemical proteomics with a photoaffinity analogue implicated the TIM23 import machinery. Genetic or pharmacological inhibition of the TIM23-PAM axis suppressed mitochondrial permeabilization without affecting canonical BAX-BAK-dependent apoptosis. These findings establish that mitochondrial protein import couples translation-associated proteotoxic stress to mitochondrial injury and identify regulation of import flux as a determinant of mitochondrial integrity during proteostasis failure.

cell biology↗

bioRxiv2021

Disrupted PDZ-domain binding motif of the dopamine transporter uniquely alters nanoscale distribution, dopamine homeostasis and reward motivation

The dopamine transporter (DAT) is part of a presynaptic multi-protein network involving interactions with scaffold proteins via its C-terminal PDZ-domain binding sequence. In a mouse model expressing DAT with mutated PDZ binding sequence (DAT-AAA), we previously demonstrated the importance of this binding sequence for striatal expression of DAT. Here we show by application of direct Stochastic Reconstruction Microscopy (dSTORM) not only that the striatal level of transporter is reduced in DAT-AAA mice, but also that the nanoscale distribution of the transporter is altered with a higher propensity of DAT-AAA to localize to irregular nanodomains in dopaminergic terminals. In parallel, we observe mesostriatal dopamine (DA) adaptations and changes in DA-related behaviors different from those seen in other genetic DAT mouse models. DA levels in striatum are reduced to [~]45% of wild type (WT), accompanied by elevated DA turnover. Nonetheless, Fast-Scan Cyclic Voltammetry recordings on striatal slices reveal a larger amplitude and prolonged clearance rate of evoked DA release in DAT-AAA mice compared to WT mice. Autoradiography and radioligand binding show reduced DA D2 receptor levels while immunohistochemistry and autoradiography show unchanged DA D1 receptor levels. In behavioral experiments, we observe enhanced self-administration of liquid food under both a fixed-ratio (FR1) and progressive-ratio (PR) schedule of reinforcement, but a reduction compared to WT when using cocaine as reinforcer. Summarized, our data demonstrate how disruption of PDZ-domain interactions causes changes in DAT expression and its nanoscopic distribution that in turn alter DA clearance dynamics.

neuroscience↗