Postnatal changes in dolichol-pathway enzyme activities in rat liver

Area of Science:

• Biochemistry
• Developmental Biology
• Molecular Biology

Background:

• Hepatic protein N-glycosylation is a crucial post-translational modification.
• Understanding its developmental regulation is key to comprehending liver function.
• The dolichol pathway is essential for N-glycan synthesis.

Purpose of the Study:

• To investigate the age-dependent changes in hepatic protein N-glycosylation in rats.
• To elucidate the role of dolichol-phosphate and oligosaccharide-lipid precursors in this process.
• To examine the activity of key enzymes in the dolichol pathway during postnatal development.

Main Methods:

• Incubation of UDP-[14C]glucose with rat liver microsomes.
• Analysis of dolichyl-phosphate [14C]glucose, [14C]glucosyl-oligosaccharide-lipid, and [14C]glycoprotein formation.
• Assay of N-glycan hexosamine content.
• Transfer of [14C]glucose and oligosaccharide to denatured alpha-lactalbumin.
• Measurement of dolichol-pathway enzyme activities (synthases).

Main Results:

• Protein N-glycosylation activity increased post-birth, peaking at 2 weeks, then decreasing to a constant level by 4 weeks.
• Dolichyl-phosphate [14C]glucose levels remained constant after 2 weeks, while [14C]glucosyl-oligosaccharide-lipid and [14C]glycoproteins decreased.
• Oligosaccharide-lipid availability appeared to be a limiting factor for N-glycosylation after 2 weeks.
• Activities of dolichol-pathway enzymes increased until 2 weeks, with a subsequent decrease in dolichyl-pyrophosphate N-acetylglucosamine synthase activity.

Conclusions:

• Hepatic protein N-glycosylation in rats undergoes significant postnatal development, peaking at 2 weeks and declining thereafter.
• The developmental pattern is influenced by the availability of oligosaccharide-lipid precursors.
• Enzyme activities within the dolichol pathway, particularly those involved in oligosaccharide assembly, regulate N-glycosylation during rat liver development.