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A lysosomal regulatory circuit essential for the development and function of microglia
Harini Iyer1, Kimberle Shen1, Ana M Meireles1
1Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Abstract:
As the primary phagocytic cells of the central nervous system, microglia exquisitely regulate their lysosomal activity to facilitate brain development and homeostasis. However, mechanisms that coordinate lysosomal activity with microglia development, chemotaxis, and function remain unclear. Here, we show that embryonic macrophages require the lysosomal guanosine triphosphatase (GTPase) RagA and the GTPase-activating protein Folliculin to colonize the brain in zebrafish. We demonstrate that embryonic macrophages in rraga mutants show increased expression of lysosomal genes but display significant down-regulation of immune- and chemotaxis-related genes. Furthermore, we find that RagA and Folliculin repress the key lysosomal transcription factor Tfeb and its homologs Tfe3a and Tfe3b in the macrophage lineage. Using RNA sequencing, we establish that Tfeb and Tfe3 are required for activation of lysosomal target genes under conditions of stress but not for basal expression of lysosomal pathways. Collectively, our data define a lysosomal regulatory circuit essential for macrophage development and function in vivo.
Insights
Embryonic brain macrophages need RagA and Folliculin for development. These proteins regulate lysosomal pathways and immune genes, ensuring proper brain colonization and function.
Area of Science:
- Neuroscience
- Cell Biology
- Immunology
Background:
- Microglia, the brain's immune cells, rely on lysosomes for development and function.
- The coordination between lysosomal activity and microglial development, migration, and immune responses is not well understood.
Purpose of the Study:
- To investigate the molecular mechanisms controlling lysosomal activity in developing brain macrophages.
- To identify key regulators of lysosomal function essential for macrophage colonization and immune gene expression in the brain.
Main Methods:
- Utilized zebrafish as a model organism to study embryonic macrophage development.
- Employed genetic manipulation (rraga mutants) and RNA sequencing to analyze gene expression.
- Investigated the role of RagA, Folliculin, Tfeb, and Tfe3 in lysosomal regulation and macrophage function.
Main Results:
- RagA (lysosomal GTPase) and Folliculin are crucial for embryonic macrophage brain colonization in zebrafish.
- Macrophages lacking RagA showed increased lysosomal gene expression but decreased immune and chemotaxis gene expression.
- RagA and Folliculin were found to repress the transcription factors Tfeb and Tfe3 in macrophages.
- Tfeb and Tfe3 are essential for stress-induced lysosomal gene activation, not basal levels.
Conclusions:
- A novel lysosomal regulatory circuit involving RagA, Folliculin, Tfeb, and Tfe3 is defined.
- This circuit is critical for regulating macrophage development, brain colonization, and immune function.
- The findings provide insights into the intricate mechanisms governing microglial biology and CNS homeostasis.
