Bioactive peptides control receptor for advanced glycated end product-induced elevation of kidney insulin receptor substrate 2 and reduce albuminuria in diabetic mice.
OBJECTIVE
Sixteen-week-old db/db mice exhibit significantly elevated blood glucose and albuminuria. Kidney mesangial cell matrix expansion and collagen IV synthesis correlate with disease progression, but the underlying mechanism is unclear.


METHODS
Adaptive biochemical datasets were generated in cultured 293 kidney cells and in db/db mice.


RESULTS
In animals receiving daily subcutaneous bolus injections (weeks 8-13) of 20 microg/day humanin or 40 microg/day protein kinase C (NPKC) (a PKC-beta2 inhibitor peptide), there was a significant reduction in albuminuria, insulin receptor substrate 2 (IRS-2) and phospho-Akt (Ser473) levels in kidney tissue extracts (p < 0.05 in all cases). Elevated IRS-2 (not IRS-1), altered Akt1 and selective phosphorylation of p-Akt/Ser473 and p-IRS-1/Ser307 (but not p-Akt/Thr308 or p-IRS-2/Ser731) are correlates of the receptor for advanced glycated end product activation and are linked to albuminuria in vivo, whereas in P38 peptide-treated animals, collagen IV synthesis can be uncoupled from albuminuria altogether.


CONCLUSIONS
Taken together, our results suggest that elevated IRS-2 and altered Akt phosphorylation may be more closely tied to the cause of diabetic kidney disease in db/db mice than mesangial matrix expansion per se, though both may originate from elevated circulatory glucose, and mesangial matrix expansion may independently exacerbate kidney dysfunction.
Mayflower Organization for Research and Education, Inc., Sunnyvale, CA 94085, USA.
Baljit K
BK
Singh
Desmond D
DD
Mascarenhas
D000419:Albuminuria / Q000378:metabolism*; D000818:Animals; D024141:Collagen Type IV / Q000378:metabolism; D003920:Diabetes Mellitus / Q000378:metabolism*; D004195:Disease Models, Animal; D017127:Glycation End Products, Advanced / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism
D024141:Collagen Type IV; D017127:Glycation End Products, Advanced; D006454:Hemoglobins; D055504:Insulin Receptor Substrate Proteins; D010455:Peptides; C514862:Akt1 protein, mouse; D051057:Proto-Oncogene Proteins c-akt