Bicarbonate-dependent secretion and proteolytic processing of recombinant myocilin

Area of Science:

• Biochemistry
• Ophthalmology
• Cell Biology

Background:

• Myocilin is an extracellular glycoprotein with an unclear function.
• Mutations in myocilin are implicated in glaucoma, a condition causing irreversible vision loss and often elevated intraocular pressure.
• Previous research indicated that recombinant myocilin undergoes intracellular proteolytic processing by calpain II, and this cleavage is reduced by glaucoma mutations.

Purpose of the Study:

• To investigate factors regulating the proteolytic processing of recombinant myocilin.
• To analyze how culture medium parameters affect the presence of the extracellular C-terminal fragment of myocilin.
• To understand the role of the N-terminal region in myocilin intracellular accumulation.

Main Methods:

• Utilized a cellular model to study recombinant myocilin processing.
• Manipulated culture medium parameters including pH and bicarbonate concentration.
• Assessed the presence of extracellular C-terminal myocilin fragment and intracellular accumulation of full-length myocilin.

Main Results:

• Extracellular bicarbonate depletion and culture medium acidification led to reversible intracellular accumulation of full-length myocilin.
• These conditions also increased intracellular proteolytic processing of myocilin, raising the extracellular C-terminal fragment percentage.
• Myocilin intracellular accumulation was found to depend on its N-terminal region.

Conclusions:

• Aqueous humor bicarbonate variations may modulate the secretion and cleavage of myocilin in ocular tissues.
• These findings provide insights into the potential mechanisms linking myocilin function to glaucoma pathophysiology.
• The study highlights the influence of environmental factors on protein processing within ocular tissues.