33 Oral - Physiology, Aging, and Metabolism I
Thursday April 07, 4:45 PM - 5:00 PM

Authors:
John Vaughen ¹; Emma Theisen ²; Ina Anreiter ²; Irma Magaly Rivas-Serna ³; Vera Mazurak ³; Thomas Clandinin ³; Tom Clandinin ²

Affiliations:
1) Stanford University, Department of Developmental Biology; 2) Stanford University, Department of Neurobiology; 3) University of Alberta, Department of Agriculture, Food, and Nutritional Science

Keywords:
r. proteostasis; k. glia

Lifelong brain health is sustained by macromolecule recycling through autophagy-lysosomal and proteasomal degradation pathways. How brains balance membrane recycling and intensive neurotransmission remains mysterious. To better understood the cellular underpinnings of brain membrane homeostasis, we investigated glucocerebrosidase (GBA), a critical lysosomal protein which hydrolyzes the sphingolipid glucosylceramide (GlcCer) and is commonly mutated in neurological diseases, including Parkinson’s. We show that Drosophila gba1b brains harbor widespread and heterogeneous proteostasis defects: engorged neural lysosomes appear during pupal development and persist throughout life, whereas ubiquitinated protein aggregates progressively afflict neurons and glia. Using cell-type specific Gba1b manipulations, we demonstrate that glial Gba1b is necessary and sufficient for regulating brain proteostasis. Which glia mediate GBA’s wide-ranging effects? Depleting Gba1b in individual glia subsets caused no detectable changes, while depletion in both barrier and ensheathing glia phenocopied panglial gba1b knockdown. Interestingly, although Gba1b overexpression in neurons was toxic, placing Gba1b directly under a neural promoter largely rescued gba1b null defects. Thus, Gba1b is made by glia but can function in neurons to control brain lipid metabolism and proteostasis.

Given these complex phenotypes, we hypothesized that differential lipid accumulation occurred across time and cell-type. We conducted targeted lipidomic across multiple ages and timepoints from gba1b brains. GlcCer species were immediately elevated in young mutant brains, and ectopic GlcCer staining colocalized with neural lysosomes. Additionally and unexpectedly, younger gba1b brains harbored certain GlcCer species only at a specific zeitgeber, while these species were always detectable in older brains. We thus re-examined young gba1b brains for aggregates across time and found transient aggregates prominently in glia processes in the optic lobe chiasms. We are exploring if this aggregate clearance cycle is under circadian clock control and/or driven by light and neural activity. Do gba1b mutants show other circadian-related phenotypes? Using activity assays, we demonstrate that gba1b mutants as well as glial gba1b knockout flies are hyperactive and sleep less but still retain circadian rhythms when housed in constant darkness. Intriguingly, other short sleeping mutants also harbor ectopic aggregates in optic chiasm glia, hinting at a connection between sleep and glia proteostasis. These studies reveal compartmentalization of sphingolipid lysosomal enzymes in glia and support the hypothesis that membrane recycling via glia is a molecular function of sleep.