Low‐dose decitabine promotes M2 macrophage polarization in patients with primary immune thrombocytopenia via enhancing KLF4 binding to PPARγ promoter

Abstract

Background The first‐line therapy is effective for the treatment of primary immune thrombocytopenia (ITP); however, maintaining the long‐term responses remains challenging. Low‐dose decitabine (DAC) has been adopted to treat refractory ITP, while its role in macrophage polarization has not been fully understood. We aimed to investigate the mechanistic role of DAC in M2 macrophage polarization and evaluated its therapeutic effect in ITP. Methods The M2 monocytes were identified by flow cytometry from peripheral blood mononuclear cells in healthy controls (HCs) and ITP patients. The expression of PPARγ, Arg‐1, DNMT3b and NLRP3, together with IL‐10 plasma levels was measured to examine its function. Bisulfite‐sequencing PCR was used to evaluate the methylation status of PPARγ promoter, and the binding affinity of KLF4 was measured by Cut&Tag. A sh‐PPARγ THP‐1 cell line was created to verify if low‐dose DAC‐modulated M2 macrophage polarization was PPARγ‐dependent. The passive ITP models were used to investigate the therapeutic effects of low‐dose DAC and its role in modulating polarization and immunomodulatory function of macrophages. NLRP3 inflammasome and reactive oxygen species were also tested to understand the downstream of PPARγ. Results The M2 monocytes with impaired immunoregulation were observed in ITP. After high‐dose dexamethasone (HD‐DXM) treatment, M2 monocytes increased significantly with the elevated expression of PPARγ, Arg‐1 and IL‐10 in CR patients. Low‐dose DAC promoted M2 macrophage polarization in a PPARγ‐dependent way via demethylating the promoter of PPARγ, especially the KLF4 binding sites. Low‐dose DAC alleviated ITP mice by restoring the M1/M2 balance and fine‐tuning immunomodulatory function of macrophages. The downstream of the PPARγ modulation of M2 macrophage polarization might physiologically antagonize NLRP3 inflammasome. Conclusions Low‐dose DAC promoted M2 macrophage polarization due to the demethylation within the promoter of PPARγ, thus enhanced the KLF4 binding affinity in ITP.

Macrophage modulation in activation process induced immune thrombocytopenia

“…(73) Meanwhile, the secondline of treatment is thrombopoietin to stimulate platelet production. (78) However, these treatments showed a higher chance of patient remission or no treatment effects. Therefore, a new alternative therapy is proposed by modulating macrophage polarization.…”

“…For instance, a therapy using a low dose of decitabine that causes demethylation of promoter peroxisome proliferator-activated receptor γ (PPARγ) and enhances the binding affinity of primer KLF4, contributing to macrophage polarization towards M2. (78)…”

New findings and new methods on macrophages in primary immune thrombocytopenia

“…Besides, they could polarize into classically activated M1 macrophages or alternatively activated M2 macrophages. In ITP, M1 shows a preferential tendency on disease onset and the M1/M2 balance recovers when remission occurs 2,3 . When macrophages polarize to M1 predominance, they also shed immune modulation on CD4+T cells 4,5 .…”