STAT3 Contributed to Mechanical Allodynia by Regulating Chemokine Expression in Astrocytes

Abstract

Background: Stat3 is involved in cell proliferation and inflammation by transcriptionally regulating gene expression. Recent studies showed that Stat3 was a pain modulator. This action might depend on its role in astrocyte proliferation. However, whether Stat3 could regulate pain processing via modulating inflammatory response in astrocytes is still not clear.

Methods: Stat3 specific siRNA oligo or synthesized chemical inhibitor (Stattic) was applied to block the Stat3 activity in primary astrocytes (in vitro study) or rat spinal cord (in vivo study). Lipopolysaccharide (LPS) was used to induce the expression of pro-inflammatory genes in astrocyte cultures and rat spinal cord. Immunofluorescence staining on cells or spinal slices was performed to monitor Stat3 activation. The impact of Stat3 inhibition on pro-inflammatory genes expression was determined by cytokine antibody array and real-time PCR. Von-Frey filaments test was used to detect the effects of stat3 inhibitor on LPS induced mechanical allodynia on rats.

Results: Intrathecal injection of LPS activated Stat3 in reactive astrocytes on rats. Blockade of Stat3 activity significantly attenuated LPS induced mechanical allodynia (Fig 1). Immunofluorescence staining revealed that this was correlated to lower level of reactive astrocytes in spinal dorsal horn. In vitro study revealed that Stat3 modulated inflammatory response in primary astrocytes by transcriptionally regulating the expression of chemokines, including CX3CL1, CXCL5, CXCL10 and CCL20 (Fig 2). Similarly, inhibition of Stat3 also reversed the expression of these chemokines in rat spinal dorsal horn.

Conclusion: Our study revealed that Stat3 acted as a regulator of reactive astrocytes by modulating the expression of chemokines in vitro and in vivo. Stat3 regulated inflammatory response in astrocytes may be responsible for its role in pain modulation. Blockade of Stat3 represents a new approach to control pain.