Prevention of insulin resistance and beta-cell loss by abrogating PKCepsilon-induced serine phosphorylation of muscle IRS-1 in Psammomys obesus.
OBJECTIVE
Psammomys obesus gerbil exhibits PKCepsilon over-expression on high-energy (HE) diet. Muscle insulin receptor (IR) signalling and tyrosine kinase activity are inhibited eliciting insulin resistance. We aimed at preventing diabetes by inhibiting PKCepsilon-induced serine phosphorylation of IRS-1 with novel PKCepsilon abrogating peptides.


METHODS
PKCepsilon abrogating peptides were copied from catalytic domain of PKC molecule (PCT patent IL2006/000755). Psammomys fed a diabetogenic HE diet received i.p. peptides KCe-12 and KCe-16 (18 mg/kg) on days 0, 7 and 14 controls received peptide solvent.


RESULTS
Food consumption and animal weight remained unchanged. On day 16, non-fasting blood glucose levels returned to normal (90 +/- 5 versus 347 +/- 16 mg/dL in untreated controls). Hyperinsulinemia fell from 584 +/- 55 to 180 +/- 22 mU/L. Western blot analysis showed that the increased phosphoserine(636, 639) content on IRS-1 in gastrocnemius muscle of diabetic animals was reduced three fold, the PKB/AKT activity increased two fold and muscle GLUT4 tended to increase, compared with controls. Likewise, administration of KCe-12 prior to placing the HE diet prevented the onset of diabetes. KCe-12 treatment did not reduce muscle PKCepsilon level. Damage and loss of insulin in pancreatic beta cells on HE diet were prevented by KCe-12, as shown in micrographs of islet hematoxylin-eosin staining and insulin immunostaining. The preserved secretory function enabled Psammomys to normalize glucose homeostasis.


CONCLUSIONS
KCe-16 and KCe-12 peptides derived from PKCepsilon substrate-binding region prevented the nutritional diabetes and protected muscle IRS-1 from PKCepsilon-induced serine phosphorylation, abrogating the insulin-signalling impediment in the Psammomys model of type 2 diabetes. Anti-diabetic peptides may lead to novel modalities preventing human overnutrition-induced insulin resistance and diabetes.
Mack
Esther
E
Diabetes Center, Hadassah University Hospital, Jerusalem, Israel.
Ziv
Ehud
E
Reuveni
Hadas
H
Kalman
Rony
R
Niv
Masha Y
MY
Jörns
Anne
A
Lenzen
Sigurd
S
Shafrir
Eleazar
E
D000818:Animals; D020134:Catalytic Domain; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy* / Q000517:prevention & control; D005260:Female; D005849:Gerbillinae; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D007333:Insulin Resistance; D050417:Insulin-Secreting Cells / Q000187:drug effects*; D009842:Oligopeptides / Q000627:therapeutic use*; D010766:Phosphorylation / Q000187:drug effects; D051744:Protein Kinase C-epsilon / Q000037:antagonists & inhibitors*; D012694:Serine / Q000378:metabolism
D055504:Insulin Receptor Substrate Proteins; D009842:Oligopeptides; D012694:Serine; D051744:Protein Kinase C-epsilon