Enhanced proteolytic activity directed against the N-terminal of IGF-I in diabetic rats

Abstract

We have recently identified in serum an acid protease which is capable of generating des(1-3)IGF-I from intact IGF-I. Here we have utilized a synthetic substrate with the sequence, biotin-G-P-E-T-L-C-BSA which contains the N-terminal sequence of IGF-I, to investigate the levels of this protease activity in streptozotocin-diabetic rats. Protease activity, quantified in terms of the amount of the biotin label lost, was determined in serum and hepatic extracts from normal control rats, diabetic rats and insulintreated diabetic rats. Both the serum protease activity and protease activity in hepatic extracts were significantly increased in diabetic rats compared with control rats (P<0·02 and P<0·005). Following acute administration of insulin, a rapid and marked reduction in serum protease activity was observed; with an 50% reduction apparent at 30 min (P<0·001). Chronic insulin treatment of diabetic rats also significantly reduced the serum and hepatic protease activity to the levels seen in control rats. A positive correlation between protease activity and serum glucose level was observed (r=0·58, P<0·005). The abundance of Spi 2·1 mRNA, a serine protease inhibitor, capable of inhibiting the IGF-I protease activity in vitro, was significantly decreased in the liver of diabetic rats and insulin treatment of diabetic rats did not normalize Spi 2·1 mRNA levels.These data suggest that the conversion of IGF-I to the more active des(1-3)IGF-I variant may be enhanced in diabetic animals. Since serum IGF-I levels are reduced in diabetic rats, increased des(1-3)IGF-I-generating protease activity would enhance the functional activity of the circulating IGF-I.

GPE Promotes the Proliferation and Migration of Mouse Embryonic Neural Stem Cells and Their Progeny In Vitro

“…Within the brain, IGF-1 is proteolytically processed by a specific acid protease, generating des-N-(1-3)-IGF-1 (des-IGF-1), and an N-terminal Gly-Pro-Glu tripeptide (GPE) [8,9,10]. Although GPE was initially considered to be a non-bioactive by-product of IGF-1, it was later found that this small peptide was able to significantly increase the release of ACh from rat cortical slices [11,12].…”

Identification and purification from the plasma of Type�1 diabetic subjects of a proteolytically active Grp94

“…Genetic factors also affect the course of complications produced by long-lasting hyperglycaemia: hyperglycaemia-induced oxidative modifications interplay in a complex way with genes [6,7], and a predisposing genetic background could explain the irreversibility of some glucose-induced damage in susceptible patients [8]. Markers for vascular complications, often apparently independent of glycaemic control, are alterations in proteolytic enzyme action [9,10,11,12] and of their inhibitors [9,13,14]. Such changes include unbalanced hyperactivation of plasma-clotting enzymes [15], but also an overall increase in proteolytic activity in various tissues and biological fluids [10,12].…”

Insulin-Like Growth Factor -1 (IGF-1) Derived Neuropeptides, a Novel Strategy for the Development of Pharmaceuticals for Managing Ischemic Brain Injury

“…A novel ion‐channel‐associated receptor was suggested to be involved in the mode of action because GPE showed only partial displacement by an N ‐methyl d ‐aspartate (NMDA) receptor antagonist in cell culture [14]. The discovery of an acid protease in both plasma and brain tissues provided further evidence for the existence of GPE as an endogenous neurobioactive peptide [15–17]. This endogenous cleavage can be enhanced in an acidic environment.…”