Zhao Yan's group reveals that the pathogenic genes WDR45 and WDR45B of nervous system diseases regulate the maturation of neuronal autophagosomes

Responsible Editor | Cellular autophagy is a highly conserved lysosome-mediated degradation pathway in eukaryotic cells.
It forms autophagosomes with a double-layer membrane structure in the cell to encapsulate and remove harmful substances in the cell.
Such as toxic protein aggregates and damaged organelles [1].

As a terminally differentiated cell, neuron cannot proliferate and renew through division, so autophagy is needed to maintain its normal function and homeostasis.

The autophagy process is mediated by a series of autophagy proteins, including the key PI(3)P effector protein Atg18 (in yeast).
Atg18 has two homologous proteins WDR45 and WDR45B in mammals [2].

Human genetic studies have found that mutations in the autophagy gene WDR45 lead to the neurodegenerative disease BPAN (β-propeller protein-associated neurodegeneration), which is a neurodegeneration with brain iron accumulation (NBIA) [3] .

The main clinical manifestations of BPAN patients are static encephalopathy in infancy, sudden Parkinson's disease in adolescence with dystonia and cognitive decline, and low signal on MRI T2-weighted image, forming a typical "tiger eye" sign.

WDR45 mutations also lead to a series of diseases with similar clinical features such as Rett syndrome, West syndrome and epilepsy.

The WDR45B mutation causes cognitive decline and mental retardation in humans, and causes a neurological disease cognitive disorder (intellectual disability, ID) that is clinically manifested as mental retardation, spastic quadriplegia, epilepsy, and cerebral hypoplasia [4].

The previous study by Zhao Yan’s research group at the University of Massachusetts Medical School constructed Wdr45 and Wdr45b single-gene knockout mice, and found that the mice showed decreased motor function and cognitive dysfunction, accompanied by swelling of a large number of axons in the brain, similar to the characteristics of BPAN and ID patients The symptoms are similar [5,6].

After knocking out both Wdr45 and Wdr45b genes at the same time, the mice showed specific nervous system autophagy block, and died one day after birth.
Autophagy in other tissues was normal, indicating that these two genes compensate each other and their functions are tissue-specific.

However, the molecular mechanism of WDR45/45B regulating the autophagy pathway is still unclear.

On February 25, 2021, Yan Zhao’s team published an article titled β-propeller proteins WDR45 and WDR45B regulate autophagosome maturation into autolysosomes in neural cells on Current Biology.

This study revealed that WDR45/45B functions in the late stage of autophagy in nerve cells, mediating the fusion process of autophagosomes and lysosomes, and promoting the formation of autophagolysosomes.

In order to study the molecular mechanism of WDR45/45B, the researchers first constructed Wdr45 and Wdr45b single knock (KO) and double knock (DKO) mouse neuroblastoma cells (Neuro-2a, N2a), and discovered Wdr45/45b DKO N2a The cells have a strong autophagy defect, while Wdr45 KO and Wdr45b KO cells have no obvious autophagy defect, which verifies that the functions of WDR45 and WDR45B compensate each other.

Wild-type WDR45 and WDR45B can reverse the autophagy defect of Wdr45/45b DKO cells, but disease-related mutants WDR45 (N61K, L98P) and WDR45B (R109Q) cannot, indicating that disease-related mutations affect the autophagy of WDR45/45B Features.

Further research found that the loss of Wdr45/45b caused the autophagosomes to become smaller and did not affect the formation of autophagosomes, but caused abnormalities in the fusion process of autophagosomes and lysosomes (see Figure 1).

 Figure 1.
Compared with control cells, the co-localization of LC3-labeled autophagosomes and LAMP1-labeled lysosomes in Wdr45/45b DKO cells significantly reduces the fusion of autophagosomes and lysosomes is a complicated and delicate process , Requires the participation of tethered protein, SNARE complex and Rab protein [7].

Researchers found that WDR45 and WDR45B interact with the tethered protein EPG5 and help it locate in late endosomes/lysosomes, thereby promoting the binding of EPG5 to SNARE proteins and regulating the fusion of autophagosomes and lysosomes (see figure 2).

In Wdr45/45b DKO cells, EPG5 is abnormally localized on autophagosomes, and the interaction with Rab7 on late endosomes/lysosomes is significantly weakened.

Qa-SNARE STX17, Qbc-SNARE SNAP29 and R-SNARE VAMP8 located on autophagosomes assemble into SNARE complexes, which mediate the fusion of autophagosomes and lysosomes.

After the deletion of Wdr45/45b, the binding of EPG5 to STX17 was enhanced, the interaction with SNAP29/VAMP8 was weakened, and the assembly of the SNARE complex was significantly reduced.

The researchers also found that disease-related WDR45/45B mutants weaken the interaction with EPG5, explaining the mechanism by which these mutations affect the autophagy function of WDR45/45B.

The above results indicate that WDR45/45B regulates the fusion process of autophagosomes and lysosomes by binding to tethered protein EPG5.

O-GlcNAcylation of SNAP29 is regulated by O-GlcNAc transferase (OGT), inhibiting O-GlcNAc-SNAP29 to promote autophagy process [8].

Knockdown of Ogt promoted the assembly of the SNARE complex in Wdr45/45b DKO cells and reversed its autophagy defect (see Figure 2).

This finding suggests that improving the fusion efficiency of autophagosomes and lysosomes can be a potential treatment for WDR45/45B-related diseases.

Figure 2.
Schematic diagram of the function of WDR45/45B in autophagy.
To sum up, this study reveals the key role and molecular mechanism of human nervous system diseases BPAN and ID pathogenic genes WDR45 and WDR45B in the late stage of autophagosome maturation.
It provides a theoretical basis for elucidating the pathogenic mechanism of related human diseases.

This study also suggests that the development of methods to promote the fusion of autophagosomes and lysosomes, such as inhibition of O-glycosylation, can be used as potential targets for the treatment of BPAN and ID.

Original link: https://doi.
org/10.
1016/j.
cub.
2021.
01.
081 Ji Cuicui, a postdoctoral fellow at the Institute of Biophysics, Chinese Academy of Sciences, is the first author of this article, and Zhao Yan, a senior research scientist at the University of Massachusetts Medical School, is the corresponding author of this article.

Zhao Yan graduated from Peking University School of Medicine, and successively conducted post-doctoral research at the Institute of Biophysics, Chinese Academy of Sciences and the University of Massachusetts Medical School.
As the first author and/or corresponding author, she has published in Molecular Cell, Current Biology, JCB, Autophagy and other internationally renowned academic journals.
He has published more than ten papers and joined the School of Life Sciences of Southern University of Science and Technology as an assistant professor in November 2020.

Zhao Yan’s research group is mainly engaged in cell biology research, using cells and mouse models to explore the molecular mechanism of autophagy and its relationship with neurodegenerative diseases, as well as the molecular composition and regulation of the interaction between the endoplasmic reticulum and various organelles Mechanism and physiological function.

We sincerely invite all young talents (postdoctoral fellows, graduate students and research assistants) to join Zhao Yan's research group.
Those who are interested, please submit your resume. Resume delivery (candidates please send application materials to): https://jinshuju.
net/f/ZqXwZt or scan the QR code to deliver the resume.
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