A Novel Role for Protein Tyrosine Phosphatase 1B as a Positive Regulator of Neuroinflammation

J Neuroinflammation. 2016 Apr 19;13(1):86. doi: 10.1186/s12974-016-0545-3.

Abstract

Background: Protein tyrosine phosphatase 1B (PTP1B) is a member of the non-transmembrane phosphotyrosine phosphatase family. Recently, PTP1B has been proposed to be a novel target of anti-cancer and anti-diabetic drugs. However, the role of PTP1B in the central nervous system is not clearly understood. Therefore, in this study, we sought to define PTP1B's role in brain inflammation.

Methods: PTP1B messenger RNA (mRNA) and protein expression levels were examined in mouse brain and microglial cells after LPS treatment using RT-PCR and western blotting. Pharmacological inhibitors of PTP1B, NF-κB, and Src kinase were used to analyze these signal transduction pathways in microglia. A Griess reaction protocol was used to determine nitric oxide (NO) concentrations in primary microglia cultures and microglial cell lines. Proinflammatory cytokine production was measured by RT-PCR. Western blotting was used to assess Src phosphorylation levels. Immunostaining for Iba-1 was used to determine microglial activation in the mouse brain.

Results: PTP1B expression levels were significantly increased in the brain 24 h after LPS injection, suggesting a functional role for PTP1B in brain inflammation. Microglial cells overexpressing PTP1B exhibited an enhanced production of NO and gene expression levels of TNF-α, iNOS, and IL-6 following LPS exposure, suggesting that PTP1B potentiates the microglial proinflammatory response. To confirm the role of PTP1B in neuroinflammation, we employed a highly potent and selective inhibitor of PTP1B (PTP1Bi). In LPS- or TNF-α-stimulated microglial cells, in vitro blockade of PTP1B activity using PTP1Bi markedly attenuated NO production. PTP1Bi also suppressed the expression levels of iNOS, COX-2, TNF-α, and IL-1β. PTP1B activated Src by dephosphorylating the Src protein at a negative regulatory site. PTP1B-mediated Src activation led to an enhanced proinflammatory response in the microglial cells. An intracerebroventricular injection of PTP1Bi significantly attenuated microglial activation in the hippocampus and cortex of LPS-injected mice compared to vehicle-injected mice. The gene expression levels of proinflammatory cytokines were also significantly suppressed in the brain by a PTP1Bi injection. Together, these data suggest that PTP1Bi has an anti-inflammatory effect in a mouse model of neuroinflammation.

Conclusions: This study demonstrates that PTP1B is an important positive regulator of neuroinflammation and is a promising therapeutic target for neuroinflammatory and neurodegenerative diseases.

Keywords: Lipopolysaccharide; Microglia; Neuroinflammation; PTP1B; Proinflammatory cytokines; Src.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Disease Models, Animal
  • Encephalitis / enzymology*
  • Encephalitis / immunology*
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Immunohistochemistry
  • Mice
  • Mice, Inbred C57BL
  • Microglia / immunology
  • Microglia / metabolism*
  • Polymerase Chain Reaction
  • Protein Tyrosine Phosphatase, Non-Receptor Type 1 / immunology
  • Protein Tyrosine Phosphatase, Non-Receptor Type 1 / metabolism*
  • Transfection

Substances

  • Protein Tyrosine Phosphatase, Non-Receptor Type 1
  • Ptpn1 protein, mouse