Abnormal PI3 kinase/Akt signal pathway in vagal afferent neurons and vagus nerve of streptozotocin-diabetic rats.
The PI3 (phosphatidylinositol-3) kinase/Akt (protein kinase B) signal pathway is involved in the molecular signaling that regulates retrograde axonal transport of neurotrophins in the nervous system. Previous work showed that a reduced retrograde axonal transport of endogenous nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the vagus nerve of diabetic rats occurred in the presence of normal production of neurotrophins and neurotrophin receptors. To assess the potential involvement of an impaired PI3 kinase/Akt signal pathway in the diabetes-induced reduction in retrograde axonal transport of neurotrophins in the vagus nerve, we characterized diabetes-induced changes in the PI3 kinase/Akt signal pathway in the vagus nerve and vagal afferent neurons. Control and streptozotocin (STZ)-induced diabetic rats with a duration of 16 weeks, kinase assays, Western blotting, and immunocytochemistry were used to show that diabetes resulted in alterations in activity and protein expression of the PI3 kinase/Akt signal pathway in the vagus nerve and vagal afferent neurons. Diabetes caused a significant decrease in enzymatic activity of PI3 kinase and Akt (52 and 36% of control, respectively) in the vagus nerve. The reduced enzymatic activity was not associated with decreased protein expression of the p85 subunit of PI3 kinase, Akt and phosphorylation of Akt (ser473). In contrast, there was a significant increase in the phosphorylation of p70s6 kinase (thr421/ser424) along with a normal protein expression of p70s6 kinase in the vagus nerve of diabetic rats. However, diabetes induced an overall decrease in immunoreactivity of the p85 subunit of PI3 kinase, phospho-Akt (ser473) and phospho-p70s6/p85s6 kinase (thr421/ser424) in vagal afferent neurons. Thus, impaired PI3 kinase/Akt signal pathway may partly account for the reduced retrograde axonal transport of neurotrophins in the vagus nerve of STZ-induced diabetic rats.
Cai
Fang
F
Department of Pharmacology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA.
Helke
Cinda J
CJ
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001370:Axonal Transport / Q000502:physiology; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology* / Q000503:physiopathology; D003929:Diabetic Neuropathies / Q000201:enzymology* / Q000503:physiopathology; D007150:Immunohistochemistry; D008297:Male; D009414:Nerve Growth Factors / Q000378:metabolism; D009416:Nerve Regeneration / Q000502:physiology; D009475:Neurons, Afferent / Q000201:enzymology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D014630:Vagus Nerve / Q000201:enzymology* / Q000503:physiopathology; D020421:Vagus Nerve Diseases / Q000201:enzymology* / Q000209:etiology / Q000503:physiopathology
D009414:Nerve Growth Factors; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C494920:Akt1 protein, rat