Depleting Cellular Retinoic Acid Binding Protein 1 Impairs UPR^mt

Area of Science:

• Neuroscience
• Cell Biology
• Mitochondrial Biology

Background:

• Mitochondrial dysfunction is central to neurodegenerative diseases.
• Cellular retinoic acid binding protein 1 (CRABP1) knockout mice exhibit motor neuron degeneration.
• CRABP1 is exclusively expressed in spinal motor neurons.

Purpose of the Study:

• To investigate the role of CRABP1 in mitochondrial function and stress response.
• To elucidate the mechanism by which CRABP1 deficiency leads to motor neuron defects.

Main Methods:

• Analysis of mitochondrial DNA content, gene expression, reactive oxygen species (ROS), and unfolded protein load in CKO mouse spinal cord.
• Assessment of superoxide dismutase 2 (SOD2) expression and activity.
• Evaluation of the mitochondrial unfolded protein response (UPRmt) pathway, including ATF5 mRNA and protein levels, and eukaryotic initiation factor-2α (eIF2α) phosphorylation.
• Validation in a CRABP1 knockdown motor neuron cell model (siCrabp1-MN1).

Main Results:

• CRABP1 deficiency led to reduced mitochondrial DNA and respiration gene expression.
• Elevated ROS and unfolded protein load were observed in CKO spinal cords.
• SOD2 expression/activity was reduced, and UPRmt was impaired, specifically ATF5 translation.
• Reduced eIF2α phosphorylation indicated a failure in stress response signaling.
• CRABP1 knockdown in motor neurons confirmed its cell-autonomous role in UPRmt execution.

Conclusions:

• CRABP1 deficiency causes mitochondrial dysfunction and neurodegeneration.
• CRABP1 plays a critical role in the UPRmt pathway.
• CRABP1 modulates eIF2α phosphorylation to facilitate ATF5 translation, essential for mitigating mitochondrial stress.