Autophagosome-lysosome fusion triggers a lysosomal response mediated by TLR9 and controlled by OCRL

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Phosphoinositides (PtdIns) are crucial regulators of cellular processes.
• Mutations in OCRL, a PtdIns(4,5)P2 5-phosphatase, lead to Lowe syndrome, a severe human genetic disorder.
• The role of OCRL in lysosomal responses to autophagosomal cargo has not been fully elucidated.

Purpose of the Study:

• To investigate the role of OCRL in a lysosomal response to autophagosomal cargo.
• To identify the specific cargo and receptor involved in this response.
• To understand how OCRL regulates phosphoinositide levels at the lysosome and its impact on autophagic flux.

Main Methods:

• Utilized cell-based assays to study lysosomal responses.
• Identified mitochondrial DNA and TLR9 as key cargo and receptor, respectively.
• Investigated the role of OCRL in regulating lysosomal phosphoinositide levels and mucolipin-1 activity.
• Examined autophagosome-lysosome fusion and autophagic flux in OCRL-depleted cells and Lowe syndrome patient cells.

Main Results:

• Identified a lysosomal response triggered by mitochondrial DNA and TLR9 cargo.
• Demonstrated that OCRL is essential for confining local increases in PtdIns(4,5)P2, which is critical for sustaining autophagic flux.
• Showed that OCRL depletion or inhibition leads to PtdIns(4,5)P2 accumulation, inhibiting the calcium channel mucolipin-1 and impairing autophagosome-lysosome fusion.
• Observed autophagosome accumulation in OCRL-deficient cells and Lowe syndrome patient kidneys.

Conclusions:

• OCRL plays a critical role in a specific lysosomal response to autophagosomal cargo, involving mitochondrial DNA and TLR9.
• Dysregulation of OCRL leads to impaired autophagosome-lysosome fusion due to PtdIns(4,5)P2 accumulation and mucolipin-1 inhibition, contributing to Lowe syndrome pathology.
• Targeting mucolipin-1 with selective agonists can restore autophagic flux in Lowe syndrome patient cells, offering a potential therapeutic strategy.