Interplay of Impaired Cellular Bioenergetics and Autophagy in PMM2-CDG

Abstract

Congenital disorders of glycosylation (CDG) and mitochondrial disorders are multisystem disorders with overlapping symptomatology. Pathogenic variants in the PMM2 gene lead to abnormal N-linked glycosylation. This disruption in glycosylation can induce endoplasmic reticulum stress, contributing to the disease pathology. Although impaired mitochondrial dysfunction has been reported in some CDG, cellular bioenergetics has never been evaluated in detail in PMM2-CDG. This prompted us to evaluate mitochondrial function and autophagy/mitophagy in vitro in PMM2 patient-derived fibroblast lines of differing genotypes from our natural history study. We found secondary mitochondrial dysfunction in PMM2-CDG. This dysfunction was evidenced by decreased mitochondrial maximal and ATP-linked respiration, as well as decreased complex I function of the mitochondrial electron transport chain. Our study also revealed altered autophagy in PMM2-CDG patient-derived fibroblast lines. This was marked by an increased abundance of the autophagosome marker LC3-II. Additionally, changes in the abundance and glycosylation of proteins in the autophagy and mitophagy pathways further indicated dysregulation of these cellular processes. Interestingly, serum sorbitol levels (a biomarker of disease severity) and the CDG severity score showed an inverse correlation with the abundance of the autophagosome marker LC3-II. This suggests that autophagy may act as a modulator of biochemical and clinical markers of disease severity in PMM2-CDG. Overall, our research sheds light on the complex interplay between glycosylation, mitochondrial function, and autophagy/mitophagy in PMM2-CDG. Manipulating mitochondrial dysfunction and alterations in autophagy/mitophagy pathways could offer therapeutic benefits when combined with existing treatments for PMM2-CDG.

Dysregulated proteome and N‐glycoproteome in ALG1‐deficient fibroblasts

“…N‐glycoproteomic profile in ALG1‐CDG patient fibroblasts revealed significant glycosylation abnormalities. Specifically, we observed a marked reduction in mature high mannose, hybrid and complex type glycans, a pattern consistent with other type 1 CDG [14, 22, 23]. This global hypoglycosylation in patient fibroblasts is consistent with that fact that ALG1 catalyzes an early and crucial step in the N‐glycosylation machinery in endoplasmic reticulum and the defect in ALG1 disrupts the synthesis of various glycan classes.…”

“…The gene ontology analysis revealed dysregulation of several biological processes including mitochondrial functions and autophagy. Interestingly, in our previous report, we also observed dysregulated autophagy and mitochondria‐associated proteins in PMM2‐CDG fibroblasts [22]. We observed an elevation in the expression of autophagy related proteins in ALG1‐CDG fibroblasts, supporting our hypothesis that the defect in N‐glycan synthesis could lead to cellular stress.…”

“…These peptides encompassed 249 distinct N‐glycan compositions and were located on 586 glycosylation sites associated with 485 glycoproteins (Figure 4A). In our recent investigations, we have consistently observed a substantial decrease in protein glycosylation levels in other CDG such as PMM2‐CDG and PGM1‐CDG [14, 22, 23]. We hypothesized that ALG1‐CDG would likewise exhibit a decrease in N‐glycosylation of multiple cellular proteins.…”

Case report: Novel genotype of ALG2-CDG and confirmation of the heptasaccharide glycan (NeuAc-Gal-GlcNAc-Man2-GlcNAc2) as a specific diagnostic biomarker

“…frontiersin.org glycosylation that has been previously shown to decrease in CDG fibroblasts (Ligezka et al, 2023). LAMP1 abundance was decreased by 76% compared to control cells (Figure 3A).…”

“…Additionally, we evaluated the presence of ALG2 and LAMP1 in the child’s fibroblasts. LAMP1 is a common marker of cellular glycosylation that has been previously shown to decrease in CDG fibroblasts ( Ligezka et al, 2023 ). LAMP1 abundance was decreased by 76% compared to control cells ( Figure 3A ).…”