E-Peptides Control Bioavailability of IGF-1

Marianne Smedegaard Hede,Agnieszka Piszczek,Tommaso Nastasi,Emarald Perlas,Nadine Winn,Nadia Rosenthal,Ekaterina Salimova,Antonio Musaro

doi:10.1371/journal.pone.0051152

Abstract

Insulin-like growth factor 1 (IGF-1) is a potent cytoprotective growth factor that has attracted considerable attention as a promising therapeutic agent. Transgenic over-expression of IGF-1 propeptides facilitates protection and repair in a broad range of tissues, although transgenic mice over-expressing IGF-1 propeptides display little or no increase in IGF-1 serum levels, even with high levels of transgene expression. IGF-1 propeptides are encoded by multiple alternatively spliced transcripts including C-terminal extension (E) peptides, which are highly positively charged. In the present study, we use decellularized mouse tissue to show that the E-peptides facilitate in vitro binding of murine IGF-1 to the extracellular matrix (ECM) with varying affinities. This property is independent of IGF-1, since proteins consisting of the E-peptides fused to relaxin, a related member of the insulin superfamily, bound equally avidly to decellularized ECM. Thus, the E-peptides control IGF-1 bioavailability by preventing systemic circulation, offering a potentially powerful way to tether IGF-1 and other therapeutic proteins to the site of synthesis and/or administration.

Highlights

Insulin-like Growth Factor-1 (IGF-1) is a potent peptide factor involved in a broad range of tissue processes including cell growth and survival, proliferation, differentiation and metabolism, but the molecular basis of these diverse functions is not well understood
Transgenic mice were generated with the four main IGF-1 splicing variants, combining the two signal peptides and two E peptides (Figure 1), controlled by the fast IIB muscle fiber-specific myosin light chain promoter (MLC1/3) and enhancer ([11], which drive expression exclusively in skeletal muscle (See Materials and Methods section)
In this study we report a novel extracellular matrix (ECM) tethering function for the C-terminal IGF-1 E peptides, which presumably reflects a biological role in maintaining high local concentrations of the growth factor at the site of synthesis

Summary

Introduction

Insulin-like Growth Factor-1 (IGF-1) is a potent peptide factor involved in a broad range of tissue processes including cell growth and survival, proliferation, differentiation and metabolism, but the molecular basis of these diverse functions is not well understood. The Igf-1 gene encodes four main pre-propeptides, combining signal peptides (SP1 or SP2) with Ea or Eb extension peptides (Figure 1). As these pre-propeptides all undergo post-translational processing to generate the same mature 70 aa IGF-1 protein, the specific roles of E-peptides in IGF-1 biology remain unclear. One of the isolated E-peptides (Eb, renamed MGF) has been reported to increase the regenerative capability of skeletal muscle, play a neuroprotective role against ischemia, and facilitate the actions of IGF-1 to improve cardiac function and mobilize resident stem cell populations [5,6,7]. Other studies suggest that E-peptides are not required for IGF-1 secretion but increase cell entry of IGF-1 from the media [8]

Methods

Results

Conclusion