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Carbon monoxide suppresses membrane expression of TLR4 via myeloid differentiation factor-2 in betaTC3 cells

Fredy Rocuts1, Yinghua Ma, Xinyu Zhang

  • 1Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|July 16, 2010
PubMed

Insights

Carbon monoxide (CO) protects transplanted islets from rejection by suppressing Toll-like receptor 4 (TLR4) activation in beta cells. CO inhibits TLR4 glycosylation and its interaction with MD-2, preventing membrane trafficking and activation.

Area of Science:

  • Immunology
  • Cell Biology
  • Transplantation Biology

Background:

  • Islet allografts face immune rejection after transplantation.
  • Carbon monoxide (CO) exposure protects transplanted islets by suppressing Toll-like receptor 4 (TLR4) activation in beta cells.
  • The precise molecular mechanisms by which CO modulates TLR4 in beta cells are not fully understood.

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying CO-mediated suppression of TLR4 activation in beta cells.
  • To investigate the role of TLR4 trafficking and its interaction with MD-2 in beta cells.
  • To determine how CO affects TLR4 glycosylation and membrane localization.

Main Methods:

  • Utilized betaTC3 insulinoma cells stably transfected with TLR4-YFP and Golgi markers.
  • Employed confocal microscopy to track subcellular TLR4 distribution.
  • Confirmed TLR4 and MD-2 interaction using immunoprecipitation.
  • Investigated the effects of MD-2 depletion and tunicamycin treatment on TLR4 trafficking.
  • Assessed CO's impact on TLR4 glycosylation and membrane trafficking.

Main Results:

  • In quiescent betaTC3 cells, TLR4 predominantly localized to the Golgi apparatus.
  • LPS stimulation induced rapid TLR4 trafficking from the Golgi to the cell membrane.
  • MD-2 depletion or N-glycosylation inhibition blocked TLR4 membrane translocation.
  • CO pre-exposure (250 ppm) inhibited TLR4 glycosylation and its interaction with MD-2, suppressing membrane trafficking.
  • CO effectively blocked LPS-induced TLR4 membrane activation.

Conclusions:

  • Myeloid differentiation factor-2 (MD-2) is essential for TLR4 glycosylation and subsequent membrane trafficking in beta cells.
  • Carbon monoxide (CO) inhibits beta cell TLR4 activation by preventing its glycosylation and blocking the TLR4-MD-2 interaction.
  • These findings provide insights into CO's protective effects against islet transplant rejection.

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