A novel phosphoglucomutase‐deficient mouse model reveals aberrant glycosylation and early embryonic lethality

Abstract

Patients with phosphoglucomutase (PGM1) deficiency, a congenital disorder of glycosylation (CDG) suffer from multiple disease phenotypes. Midline cleft defects are present at birth. Overtime, additional clinical phenotypes, which include severe hypoglycemia, hepatopathy, growth retardation, hormonal deficiencies, hemostatic anomalies, frequently lethal, early‐onset of dilated cardiomyopathy and myopathy emerge, reflecting the central roles of the enzyme in (glycogen) metabolism and glycosylation. To delineate the pathophysiology of the tissue‐specific disease phenotypes, we constructed a constitutive Pgm2 (mouse ortholog of human PGM1)‐knockout (KO) mouse model using CRISPR‐Cas9 technology. After multiple crosses between heterozygous parents, we were unable to identify homozygous life births in 78 newborn pups (P = 1.59897E‐06), suggesting an embryonic lethality phenotype in the homozygotes. Ultrasound studies of the course of pregnancy confirmed Pgm2‐deficient pups succumb before E9.5. Oral galactose supplementation (9 mg/mL drinking water) did not rescue the lethality. Biochemical studies of tissues and skin fibroblasts harvested from heterozygous animals confirmed reduced Pgm2 enzyme activity and abundance, but no change in glycogen content. However, glycomics analyses in serum revealed an abnormal glycosylation pattern in the Pgm2+/− animals, similar to that seen in PGM1‐CDG.

Mendelian gene identification through mouse embryo viability screening

“…This somehow counterintuitive observation has been reported for other IEM disorders 44,45 . When exploring early lethality annotations in humans, up to 39% of the known biallelic IEM genes have records of lethality before or shortly after birth, showing that a considerable proportion of these conditions in humans are life threatening, leading to early death if untreated.…”

“…In fact, for the four candidate genes highlighted in our study, it is the heterozygous mouse model which is mimicking the phenotypes observed in patients carrying biallelic mutations. This somehow counterintuitive observation has been reported for other IEM disorders 44,45 .…”

DYRK3 phosphorylates SNAPIN to regulate axonal retrograde transport and neurotransmitter release

“…Moreover, zinc finger protein 350, acetyl CoA acyltransferase, membrane-associated guanylate kinase, and two members of the DnaJ heat-shock protein family were found to be novel binding proteins of DYRK3. Although PGM1 plays a fundamental role in glycolysis, glycogenesis, and glycogenolysis [ 18 ], both ADAM22 and SNAPIN are closely related to the synaptic transmission of neurotransmitters [ 19 ]. Among these proteins, SNAPIN was chosen as a target of further analysis because some reports demonstrated that proper action of SNAPIN is critical for neuronal homeostasis, which is primarily attributed to the efficient axonal retrograde transport of various molecules via the mitochondria and autophagosome, as well as by precise synaptic neurotransmitter secretion [ 9 , 20 ].…”

Systematic Review: Drug Repositioning for Congenital Disorders of Glycosylation (CDG)

“…New techniques such as clustered regularly interspaced short palindromic Repeats (CRISPR)/Cas9 or conditional knockouts [ 42 ] have made in vivo gene engineering more accessible and efficient. In the past five years, several in vivo models have been developed for CDG, allowing the identification of pathophysiologic mechanisms [ 43 , 44 , 45 ] and the pre-clinical testing of drug repositioning candidates [ 46 , 47 ]. A compilation of both in vitro and in vivo disease models reported since October 2017 is presented in Table 2 .…”