Interplay between Akt and p38 MAPK pathways in the regulation of renal tubular cell apoptosis associated with diabetic nephropathy.
Hyperglycemia induces p38 MAPK-mediated renal proximal tubular cell (RPTC) apoptosis. The current study hypothesized that alteration of the Akt signaling pathway by hyperglycemia may contribute to p38 MAPK activation and development of diabetic nephropathy. Immunoblot analysis demonstrated a hyperglycemia-induced increase in Akt phosphorylation in diabetic kidneys at 1 mo, peaking at 3 mo, and dropping back to baseline by 6 mo. Immunohistochemical staining with anti-pAkt antisera localized Akt phosphorylation to renal tubules. Maximal p38 MAPK phosphorylation was detected concomitant with increase in terminal uridine deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells and caspase-3 activity in 6-mo diabetic kidneys. Exposure of cultured RPTCs to high glucose (HG; 22.5 mM) significantly increased Akt phosphorylation at 3, 6, and 9 h, and decreased thereafter. In contrast, p38 MAPK phosphorylation was detected between 9 and 48 h of HG treatment. Increased p38 MAPK activation at 24 and 48 h coincided with increased apoptosis, demonstrated by increased caspase-3 activity at 24 h and increased TUNEL-positive cells at 48 h of HG exposure. Blockade of p38 cascade with SB203850 inhibited HG-induced caspase-3 activation and TUNEL-positive cells. Overexpression of constitutively active Akt abrogated HG-induced p38 MAPK phosphorylation and RPTC apoptosis. In addition, blockade of the phosphatidylinositol-3 kinase/Akt pathway with LY294002 and silencing of Akt expression with Akt small interfering RNA induced p38 MAPK phosphorylation in the absence of HG. These results collectively suggest that downregulation of Akt activation during long-term hyperglycemia contributes to enhanced p38 MAPK activation and RPTC apoptosis. Mechanism of downregulation of Akt activation in 6-mo streptozotocin diabetic kidneys was attributed to decreased Akt-heat shock protein (Hsp) 25, Akt-p38 interaction, and decreased PTEN activity. Thus PTEN or Hsp25 could serve as potential therapeutic targets to modulate Akt activation and control p38 MAPK-mediated diabetic complications.
Rane
Madhavi J
MJ
Department of Medicine, University of Louisville, Louisville, Kentucky 40202, USA. mjrane01@gwise.louisville.edu
Song
Ye
Y
Jin
Shunying
S
Barati
Michelle T
MT
Wu
Rui
R
Kausar
Hina
H
Tan
Yi
Y
Wang
Yuehui
Y
Zhou
Guihua
G
Klein
Jon B
JB
Li
Xiaokun
X
Cai
Lu
L
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000378:metabolism*; D003928:Diabetic Nephropathies / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013311:Streptozocin; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D000099190:MAP-Kinase-Activated Kinase 2
D053148:Caspase 3; D047908:Intracellular Signaling Peptides and Proteins; D051059:PTEN Phosphohydrolase; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D013311:Streptozocin; D048051:p38 Mitogen-Activated Protein Kinases; D000099190:MAP-Kinase-Activated Kinase 2