Arginine Supplementation Promotes Extracellular Matrix and Metabolic Changes in Keratoconus.

Tina B Mckay,Tyler Rowsey,Shrestha Priyadarsini,Dimitrios Karamichos

doi:10.3390/cells10082076

Abstract

Keratoconus (KC) is a common corneal ectatic disease that affects 1:500–1:2000 people worldwide and is associated with a progressive thinning of the corneal stroma that may lead to severe astigmatism and visual deficits. Riboflavin-mediated collagen crosslinking currently remains the only approved treatment to halt progressive corneal thinning associated with KC by improving the biomechanical properties of the stroma. Treatments designed to increase collagen deposition by resident corneal stromal keratocytes remain elusive. In this study, we evaluated the effects of arginine supplementation on steady-state levels of arginine and arginine-related metabolites (e.g., ornithine, proline, hydroxyproline, spermidine, and putrescine) and collagen protein expression by primary human corneal fibroblasts isolated from KC and non-KC (healthy) corneas and cultured in an established 3D in vitro model. We identified lower cytoplasmic arginine and spermidine levels in KC-derived constructs compared to healthy controls, which corresponded with overall higher gene expression of arginase. Arginine supplementation led to a robust increase in cytoplasmic arginine, ornithine, and spermidine levels in controls only and a significant increase in collagen type I secretion in KC-derived constructs. Further studies evaluating safety and efficacy of arginine supplementation are required to elucidate the potential therapeutic applications of modulating collagen deposition in the context of KC.

Highlights

Arginine is a conditional essential amino acid important in protein synthesis and signal transduction in mammalian cells [1]
As an extension of that work, our current study explored the effects of arginine supplementation on extracellular matrix (ECM) secretion and metabolic flux in non-KC human corneal fibroblasts (HCFs) and human keratoconus cells (HKCs) cultured in a 3D in vitro stromal model to determine if increasing extracellular arginine levels can promote collagen secretion
Arginine metabolism proceeds through ornithine, which can be metabolized to the polyamines, spermidine and putrescine, or proline and hydroxyproline metabolites (Figure 2a)

Summary

Introduction

Arginine is a conditional essential amino acid important in protein synthesis and signal transduction in mammalian cells [1]. Arginine can be absorbed from the diet or biosynthesized from glutamate depending on the nutritional status of the organism [2,3]. Arginine plays a fundamental role in the production of many other metabolites, including the polyamines—spermidine and putrescine—that function in regulating cell proliferation and DNA replication [4]. Arginine is an important metabolite that can serve as a precursor to proline and hydroxyproline, which are both highly present in collagen monomers. Arginine has been reported to play an important role in the maintenance of immune privilege in the cornea with inhibition of arginase activity associated with graft rejection [9]

Methods

Results

Conclusion