Objectives:
Inflammation in the brain that occurs after cerebral infarction exacerbates neurological symptoms and cerebral edema, causing a great influence on the neurological prognosis of stroke patients. Inflammation in ischemic stroke is triggered by tissue-derived endogenous inflammatogenic molecules called as DAMPs (damage-associated molecular patterns). We have previously identified MSR1 as an important scavenger receptor for the removal of DAMPs from the ischemic brain. However, the factors promoting the expression level of scavenger receptors for the acceleration of DAMP clearance have not been identified. In this study, we tried to identify the previously unknown MSR1 inducing factors.
 
Methods:
To identify the MSR1 inducing factor, we used ATAC-seq analysis of infiltrating macrophage isolated from the ischemic brain. The transcription factors (TFs) which possibly bind to the open chromatin regions of Msr1 gene promoter or enhancer region were determined by TF motif analysis. The MSR1 expression level of macrophage-like RAW264.7 cell line overexpressing these transcription factors was examined by FACS and quantitative PCR. To examine the cellular uptake of DAMPs, fluorescence-conjugated DAMP molecules were added to the culture of RAW264.7 cells. The internalization of fluorescence-conjugated DAMP molecules within RAW264.7 was examined by FACS and fluorescent microscopy.
 
Results:
The lentiviral overexpression of MSR1 in myeloid cells increased the uptake of DAMP molecules such as amyloid beta peptide and peroxiredoxin family proteins (PRXs). We identified five open chromatin regions in the Msr1 gene promoter or enhancer region. The TF motif analysis using the DNA sequences of these open chromatin regions revealed the possibility that TF family members such as AP-1 and GATAs bound to the upstream of the Msr1 gene. We identified several transcription factors as an inducer of MSR1 expression for the accelerated clearance of DAMP molecules. Thus, targeting scavenger-inducing transcription factors may be a useful therapeutic strategy for ischemic stroke.