Beyond ERAD: N‐glycanase will bring you to tears

Abstract

Patients with mutations in NGLY1 cannot make tears (alacrima), have global developmental delay, movement disorder and liver dysfunction. N‐glycanase 1 (NGLY1) de‐glycosylates misfolded N‐glycosylated proteins in the cytoplasm as part of the ERAD pathway prior to their proteasomal degradation. Surprisingly, NGLY1‐deficient patient cells do not accumulate cytoplasmic misfolded N‐glycoproteins, suggesting a more complex function. Interestingly, new studies show NGLY1 is needed for transcription factor NFE2L1/NRF1 activation and normal mitochondrial function.Using WT and NGLY1‐deficient mouse embryonic fibroblasts (MEFs) we found that NGLY1‐deficient cells were resistant to hypotonic lysis compared to WT. The same was seen in NGLY1‐patient fibroblasts. Additionally, MEFs deficient in both NGLY1 and ENGase (another deglycosylation enzyme) were even more resistant to hypotonic lysis compared to NGLY1‐deficient cells. Water influx and cell swelling precedes cell lysis. We found that NGLY1‐deficient MEFs swell slower than WT MEFs. Since aquaporins (AQP) transport water, we hypothesized that AQP levels might be disrupted in NGLY1‐deficient cells. We found both AQP1 mRNA and protein were reduced in NGLY1‐deficient MEFs. shRNA knockdown of AQP1 in WT MEFs decreased hypotonic lysis, suggesting AQP1 is associated with hypotonic lysis. NGLY1 shRNA and CRISPR studies confirmed that NGLY1 regulates AQP1 levels and hypotonic cell lysis. Preliminary studies show that complementing NGLY1‐deficient MEFs with NGLY1 increases AQP1 and restores hypotonic lysis. Current efforts are directed towards understanding whether NGLY1 enzyme activity is necessary for AQP regulation. 13 types of AQP are expressed in different cell types. Our preliminary data suggest that AQP11 levels are disrupted in NGLY1‐deficient patient cells and CRISPR cells, suggesting that NGLY1 might regulate different types of AQP.We have identified a novel function of NGLY1, i.e. to directly/indirectly regulate AQPs. This finding may relate to NGLY1‐deficient patients' inability to make tears. Future efforts will try to identify NGLY1‐dependent transcription factors responsible for regulating AQPs. This work is supported by the Bertrand Might Research Fund and NGLY1.org.Support or Funding InformationThis work is supported by the Bertrand Might Research Fund.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.