Akt kinase regulates numerous cell functions including glucose
metabolism, cell growth, survival, protein synthesis, and control
of local hemodynamics. mTOR is one of down-stream effectors of
Akt involved in the initiation of protein translation. However,
renal Akt signaling in Type 1 diabetes (DM) in vivo, in particular
under the conditions reflecting differences in metabolic control,
has received less attention. Renal cortical activity and expression
of Akt and mTOR (kinase assay, western blotting) were
determined in streptozotocin-diabetic rats (D) with different
levels of glycemic control (blood glucose 22.0±1.0, 13.4±1.5,
8.1±0.4 mmol/l, p<0.05 between the groups), achieved by
varying insulin treatment (0, 4 and 12 IU/day), and in control
rats with (C4) or without (C) chronic insulin administration. Renal
Akt activity was reduced in D rats without insulin treatment and
severe hyperglycemia (D-0, -62 %, p<0.01 vs. C), partially
restored in moderately hyperglycemic rats (D-4, -30 %, p<0.05
vs. C), and normalized in D rats with intensive insulin and tight
metabolic control (D-12). Expression of active mTOR paralleled
Akt activity in D-0 (-51 %, p<0.01 vs. C), but not in D-4 and D12 that demonstrated increases in active mTOR (+55 %, +80 %
resp., p<0.05) as compared to C. Moreover, insulin activated
renal Akt (+82 %, p<0.01), but not mTOR in C4. In conclusion,
glycemic control and intensity of insulin treatment are important
modulators of renal Akt and mTOR activity in diabetes. While Akt
activity is reversible by tight metabolic control, combination of
hyperglycemia and insulin treatment resulted in enhancement of
mTOR activity. In addition to Akt, other signaling pathways likely
contribute to regulation of renal mTOR activity in diabetes.