Contributions
Type: Publication Only
Background
Severe Congenital Neutropenia type 4 (SCN4) is a rare autosomal recessive disease due to mutations in the glucose-6-phosphatase beta (G6PC3) gene. G6PC3 is a typical metabolic enzyme in the endoplasmic reticulum (ER) suggested hydrolyzing glucose-6-phopshate (G6P) in glucose and phosphate. This enzyme catalyzes the final step of glycogenolysis in non gluconeogenic tissues like neutrophils. In the lumen of ER glucose-6-phosphate can be metabolized by hexose-6-phosphate dehydrogenase (H6PD) as well, which is responsible for ER redox homeostasis. The first diagnosed patient in our country has a non-sense mutation in the first exon at position W73Term causing a lack of G6PC3. Beyond severe inborn neutropenia and consequent inflammatory episodes the phenotype comprises other anomalies including congenital heart defects, urogenital anomalies prominent superficial veins, facial dysmorphism, growth and developmental delay.
Aims
The question arises as to what kind of disturbances can cause a defect of a metabolic enzyme leading to developmental malignancies - beyond affecting neutrophils? Since data are already presented in G6PC3 KO mice, we were interested in the differences or similarities between human and rodent WBC-s.
Methods
Whole blood from healthy and patient with SCN4 was collected and purified obtaining total white blood cell (WBC) fraction. Enzymatic and Western-blot measurements were made on these protein samples.
Results
Neutrophils from G6PC3-deficient WBC-s proved the lack of G6PC3 on Western blot, and also on the enzymatic level. Surprisingly we could not identify any metabolic aberrations in G6PC3-deficient WBC-s. G6PC3 deficient cells showed increased level of Grp78 and phosphorylated eIF2-α compared to the control one. Other ER stress enzymes are still under investigation. Interestingly H6PD was also decreased in the mutant cells vs. control cells.
Summary
Lack of G6P reduction or hydrolysis suggests that endoplasmic reticulum stress can be responsible for increased apoptosis in G6PC3-deficient neutrophils. However, the involvement of the PERK-eIF2α-ATF4 signaling pathway in SCN4 is still unclear, these alterations may at least in part be responsible for the phenotype of G6PC3 deficiency. Our results suggest that trying to maintain the ER redox environment with small molecules, like ascorbic acid, may help in neutrophil granulocyte surviving. We continue our investigations towards this direction.
This work was supported by the Hungarian Scientific Research Fund OTKA 101226
Keyword(s): Apoptosis, Inherited disease, Neutrophil function
Session topic: Publication Only
Type: Publication Only
Background
Severe Congenital Neutropenia type 4 (SCN4) is a rare autosomal recessive disease due to mutations in the glucose-6-phosphatase beta (G6PC3) gene. G6PC3 is a typical metabolic enzyme in the endoplasmic reticulum (ER) suggested hydrolyzing glucose-6-phopshate (G6P) in glucose and phosphate. This enzyme catalyzes the final step of glycogenolysis in non gluconeogenic tissues like neutrophils. In the lumen of ER glucose-6-phosphate can be metabolized by hexose-6-phosphate dehydrogenase (H6PD) as well, which is responsible for ER redox homeostasis. The first diagnosed patient in our country has a non-sense mutation in the first exon at position W73Term causing a lack of G6PC3. Beyond severe inborn neutropenia and consequent inflammatory episodes the phenotype comprises other anomalies including congenital heart defects, urogenital anomalies prominent superficial veins, facial dysmorphism, growth and developmental delay.
Aims
The question arises as to what kind of disturbances can cause a defect of a metabolic enzyme leading to developmental malignancies - beyond affecting neutrophils? Since data are already presented in G6PC3 KO mice, we were interested in the differences or similarities between human and rodent WBC-s.
Methods
Whole blood from healthy and patient with SCN4 was collected and purified obtaining total white blood cell (WBC) fraction. Enzymatic and Western-blot measurements were made on these protein samples.
Results
Neutrophils from G6PC3-deficient WBC-s proved the lack of G6PC3 on Western blot, and also on the enzymatic level. Surprisingly we could not identify any metabolic aberrations in G6PC3-deficient WBC-s. G6PC3 deficient cells showed increased level of Grp78 and phosphorylated eIF2-α compared to the control one. Other ER stress enzymes are still under investigation. Interestingly H6PD was also decreased in the mutant cells vs. control cells.
Summary
Lack of G6P reduction or hydrolysis suggests that endoplasmic reticulum stress can be responsible for increased apoptosis in G6PC3-deficient neutrophils. However, the involvement of the PERK-eIF2α-ATF4 signaling pathway in SCN4 is still unclear, these alterations may at least in part be responsible for the phenotype of G6PC3 deficiency. Our results suggest that trying to maintain the ER redox environment with small molecules, like ascorbic acid, may help in neutrophil granulocyte surviving. We continue our investigations towards this direction.
This work was supported by the Hungarian Scientific Research Fund OTKA 101226
Keyword(s): Apoptosis, Inherited disease, Neutrophil function
Session topic: Publication Only