Reducing INS-IGF1 signaling protects against non-cell autonomous vesicle rupture caused by SNCA spreading

ABSTRACT

Aging is associated with a gradual decline of cellular proteostasis, giving rise to devastating protein misfolding diseases, such as Alzheimer disease (AD) or Parkinson disease (PD). These diseases often exhibit a complex pathology involving non-cell autonomous proteotoxic effects, which are still poorly understood. Using Caenorhabditis elegans we investigated how local protein misfolding is affecting neighboring cells and tissues showing that misfolded PD-associated SNCA/α-synuclein is accumulating in highly dynamic endo-lysosomal vesicles. Irrespective of whether being expressed in muscle cells or dopaminergic neurons, accumulated proteins were transmitted into the hypodermis with increasing age, indicating that epithelial cells might play a role in remote degradation when the local endo-lysosomal degradation capacity is overloaded. Cell biological and genetic approaches revealed that inter-tissue dissemination of SNCA was regulated by endo- and exocytosis (neuron/muscle to hypodermis) and basement membrane remodeling (muscle to hypodermis). Transferred SNCA conformers were, however, inefficiently cleared and induced endo-lysosomal membrane permeabilization. Remarkably, reducing INS (insulin)-IGF1 (insulin-like growth factor 1) signaling provided protection by maintaining endo-lysosomal integrity. This study suggests that the degradation of lysosomal substrates is coordinated across different tissues in metazoan organisms. Because the chronic dissemination of poorly degradable disease proteins into neighboring tissues exerts a non-cell autonomous toxicity, this implies that restoring endo-lysosomal function not only in cells with pathological inclusions, but also in apparently unaffected cell types might help to halt disease progression.

Abbreviations: AD: Alzheimer disease; BM: basement membrane; BWM: body wall muscle; CEP: cephalic sensilla; CLEM: correlative light and electron microscopy; CTNS-1: cystinosin (lysosomal protein) homolog; DA: dopaminergic; DAF-2: abnormal dauer formation; ECM: extracellular matrix; FLIM: fluorescence lifetime imaging microscopy; fps: frames per second; GFP: green fluorescent protein; HPF: high pressure freezing; IGF1: insulin-like growth factor 1; INS: insulin; KD: knockdown; LMP: lysosomal membrane permeabilization; MVB: multivesicular body; NOC: nocodazole; PD: Parkinson disease; RFP: red fluorescent protein; RNAi: RNA interference; sfGFP: superfolder GFP; SNCA: synuclein alpha; TEM: transmission electron microscopy; TNTs: tunneling nanotubes; TCSPC: time correlated single photon counting; YFP: yellow fluorescent protein.

KEYWORDS:

• Alpha-synuclein
• aging
• intercellular spreading
• lysosomal homeostasis
• lysosomal membrane permeabilization
• neurodegenerative diseases
• non-cell autonomous toxicity
• proteostasis

Acknowledgments

We thank Dr. Richard I. Morimoto for his support during the early stages of this project and Dr. Olivia Casanueva and Dr. Axel Mogk for helpful discussion and constructive comments on this manuscript. The CLEM work and electron microscopy was done by Dr. Charlotta Funaya at the Electron Microscopy Core Facility (EMCF) of Heidelberg University. We would like to acknowledge the EMCF for their support. We further acknowledge the help of Nicholas Xiao with generating the WT and A53T mutant myo-3p::SNCA::RFP strains, and the help of Sonja Sinn with integrating the dat-1p::SNCA::RFP transgene. We are grateful to Dr. Claire Richardson and Dr. Kang Shen for supplying the strain TV14687 and to Dr. Harald Hutter for sharing the strain VH95. Dr. Xiaochen Wang generously provided nematodes expressing the transgenes qxIs66 and qxIs281. The strain EG6147 was kindly provided by Dr. Erik Jorgensen. The strain BIJ34 and a pPD49.26 expression plasmid coding for sfGFP::LGALS3 were a kind gift of Dr. Bin Liu and Dr. Marja Jäättelä. Some strains were provided by the Caenorhabditis Genetics Center (CGC), which is funded by NIH Office of Research Infrastructure Programs (P40 OD010440).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Material

Supplementary material for this article can be accessed here.

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft under Grant [KI-1988/3-1] and [NeuroCure Excellence Cluster] to J.K., as well as Grant [SFB1036 TP20] to C.N.K., and a Fulbright Association Scholar Award to C.V.