Hypoxia activates MAPK activity in rat nucleus pulposus cells: regulation of integrin expression and cell survival.
OBJECTIVE
The aim of the present study was to investigate whether activation of MAPK subtypes ERK and p38 influences integrin expression and promotes nucleus pulposus cell survival in hypoxia.


BACKGROUND
We have recently shown that in a low oxygen environment, rat nucleus pulposus cells activate phosphatidylinositol 3-kinase/Akt (PI3K/Akt) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling pathways. However, the role of these signaling pathways in regulating cell matrix interactions is not known.


METHODS
Rat nucleus pulposus cells were cultured in hypoxia (2% O2) or normoxia (20% O2). Western blotting and kinase assay were used to analyze expression of MAPK signaling molecules. Cell attachment to collagen was studied using an adhesion assay, whereas flow cytometry and RT-PCR were performed to quantify integrin receptor expression.


RESULTS
In a hypoxic environment (2% O2), rat nucleus pulposus cells showed a persistent phosphorylation of p38 and ERK proteins; pERK catalyzed the phosphorylation of Elk1-Gst fusion protein. When ERK activity was blocked, cell adhesion to Type II collagen, one of the major extracellular matrix proteins in the nucleus pulposus tissue, was impaired. A similar inhibitory effect on collagen adhesion was observed when nucleus pulposus cells were treated with an antibody to alpha2 integrin. Furthermore, when ERK activity was inhibited, there was a decrease in alpha2 integrin mRNA expression. In contrast to ERK, inhibition of p38 activity did not modulate alpha2 integrin subunit mRNA expression. Likewise, inhibition of ERK, but not p38, resulted in downregulation of nucleus pulposus alpha2 integrin protein levels and blocked cell survival in hypoxia.


CONCLUSIONS
Hypoxia activated MAPK signaling pathway activity in nucleus pulposus cells. ERK, but not p38, regulated alpha2 integrin expression and cell survival.
Risbud
Makarand V
MV
Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA 19107, USA. makarand.risbud@jefferson.edu
Guttapalli
Asha
A
Albert
Todd J
TJ
Shapiro
Irving M
IM
D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D024043:Collagen Type II / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism*; D039421:Integrin alpha2 / Q000235:genetics* / Q000378:metabolism; D007403:Intervertebral Disc / Q000166:cytology* / Q000201:enzymology*; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D024043:Collagen Type II; D039421:Integrin alpha2; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010100:Oxygen