FBXL4 deficiency increases mitochondrial removal by autophagy

Area of Science:

• Cell Biology
• Genetics
• Mitochondrial Biology

Background:

• Pathogenic variants in FBXL4 gene are linked to severe encephalopathic syndromes.
• These syndromes are characterized by mitochondrial DNA (mtDNA) depletion and impaired oxidative phosphorylation.
• The exact pathophysiology of FBXL4 deficiency remains poorly understood.

Purpose of the Study:

• To investigate the role of FBXL4 in mitochondrial homeostasis.
• To elucidate the mechanisms underlying FBXL4 deficiency-induced mitochondrial dysfunction.
• To understand the link between FBXL4, autophagy, and mitochondrial disease.

Main Methods:

• Generation of homozygous Fbxl4 knockout mice.
• Analysis of mitochondrial and lysosomal protein levels in knockout mice and cells.
• Assessment of mitochondrial content and turnover using patient-derived fibroblasts and knockout cell lines.
• Pharmacological inhibition of lysosomal and proteasomal pathways.

Main Results:

• Fbxl4 knockout mice exhibit perinatal lethality and delayed-onset mitochondrial dysfunction.
• Surviving knockout animals show reduced mitochondrial proteins and mtDNA depletion.
• Lysosomal proteins are upregulated, and mitochondrial turnover is increased in Fbxl4-deficient cells.
• Inhibition of lysosomal function rescues the mitochondrial phenotype, while proteasomal inhibition has no effect.

Conclusions:

• FBXL4 functions as a negative regulator of mitochondrial autophagy.
• Loss of FBXL4 leads to excessive mitochondrial removal, causing decreased mitochondrial content.
• FBXL4 deficiency results in mitochondrial disease due to impaired mitochondrial homeostasis.