Endogenous BDNF augments NMDA receptor phosphorylation in the spinal cord via PLCγ, PKC, and PI3K/Akt pathways during colitis.
BACKGROUND
Spinal central sensitization is an important process in the generation and maintenance of visceral hypersensitivity. The release of brain-derived neurotrophic factor (BDNF) from the primary afferent neurons to the spinal cord contributes to spinal neuronal plasticity and increases neuronal activity and synaptic efficacy. The N-Methyl-D-aspartic acid (NMDA) receptor possesses ion channel properties, and its activity is modulated by phosphorylation of its subunits including the NMDA receptor 1 (NR1).


METHODS
Colonic inflammation was induced by a single dose of intracolonic instillation of tri-nitrobenzene sulfonic acid (TNBS). NR1 phosphorylation by BDNF in vivo and in culture was examined by western blot and immunohistochemistry. Signal transduction was studied by direct examination and use of specific inhibitors.


RESULTS
During colitis, the level of NR1 phospho-Ser(896) was increased in the dorsal horn region of the L1 and S1 spinal cord; this increase was attenuated by injection of BDNF neutralizing antibody to colitic animals (36 μg/kg, intravenous (i.v.)) and was also reduced in BDNF(+/-) rat treated with TNBS. Signal transduction examination showed that the extracellular signal-regulated kinase (ERK) activation was not involved in BDNF-induced NR1 phosphorylation. In contrast, the phosphatidylinositol 3-kinase (PI3K)/Akt pathway mediated BDNF-induced NR1 phosphorylation in vivo and in culture; this is an additional pathway to the phospholipase C-gamma (PLCγ) and the protein kinase C (PKC) that was widely considered to phosphorylate NR1 at Ser(896). In spinal cord culture, the inhibitors to PLC (U73122), PKC (bisindolylmaleimide I), and PI3K (LY294002), but not MEK (PD98059) blocked BDNF-induced NR1 phosphorylation. In animals with colitis, treatment with LY294002 (50 μg/kg, i.v.) blocked the Akt activity as well as NR1 phosphorylation at Ser(896) in the spinal cord.


CONCLUSIONS
BDNF participates in colitis-induced spinal central sensitization by up-regulating NR1 phosphorylation at Ser(896). The PI3K/Akt pathway, in addition to PLCγ and PKC, mediates BDNF action in the spinal cord during colitis.
Department of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University School of Medicine, 1220 East Broad Street MMRB 5046, Richmond, VA, 23298-0551, USA. mliu3@vcu.edu.
Miao
M
Liu
Department of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University School of Medicine, 1220 East Broad Street MMRB 5046, Richmond, VA, 23298-0551, USA. jkay4223@gmail.com.
Jarren C
JC
Kay
Department of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University School of Medicine, 1220 East Broad Street MMRB 5046, Richmond, VA, 23298-0551, USA. sshen@vcu.edu.
Shanwei
S
Shen
Department of Physiology and Biophysics, Internal Medicine Gastroenterology, Virginia Commonwealth University School of Medicine, 1220 East Broad Street MMRB 5046, Richmond, VA, 23298-0551, USA. lqiao2@vcu.edu.
Li-Ya
LY
Qiao
D000818:Animals; D000906:Antibodies / Q000627:therapeutic use; D019208:Brain-Derived Neurotrophic Factor / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D002867:Chromones / Q000627:therapeutic use; D003092:Colitis / Q000188:drug therapy / Q000209:etiology / Q000473:pathology*; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors; D008297:Male; D009025:Morpholines / Q000627:therapeutic use; D009924:Organ Culture Techniques; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014302:Trinitrobenzenesulfonic Acid / Q000633:toxicity; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D000906:Antibodies; D019208:Brain-Derived Neurotrophic Factor; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; C409466:NR1 NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014302:Trinitrobenzenesulfonic Acid; D058539:Phosphatidylinositol 3-Kinase; D011493:Protein Kinase C