Overexpression of CIRP in astrocytes contributes to Alzheimer’s disease via downregulation of uPA

Background: Cold inducible RNA-binding protein (CIRP) is an important danger-associated molecular pattern involved in tissue-specific and systemic inflammation and is also regarded as a potential regulator of Alzheimer’s disease (AD). However, the precise roles and mechanism of CIRP in the functional changes in astrocytes during the development of AD are still unknown. This study aimed to assess gene expression alterations in astrocytes after they overexpress CIRP (oe-CIRP) and to explore the relationship between abnormal CIRP expression and AD. Methods: We established astrocyte cell lines that stably expressed CIRP or control vectors using 3 different kinds of human glioma cell lines, namely, U87, U251 and H4, and analyzed the mRNA expression profiles of 3 pairs of cells via microarray. Then, the significantly differentially expressed mRNAs between the CIRP-overexpressing (ov-CIRP) group and the control group were identified by bioinformatics analysis and validated by quantitative real-time PCR (q-PCR) and western blotting (WB). Finally, the effect of CIRP overexpression in astrocytes on neurons was observed in a coculture system. Results: We identified 119 mRNAs with obvious fold changes between the ov-CIRP and control groups for all 3 pairs of human glioma cell lines. These mRNAs are associated with diseases such as asthma IgE, dehydroepiandrosterone, rheumatoid arthritis, autism spectrum disorder, AD and so on. The biological functional analysis indicated that urokinase plasminogen activator (uPA), a gene whose expression significantly decreased after CIRP overexpression, was closely associated with AD. The results from q-PCR and WB assays confirmed that overexpression of CIRP significantly inhibited uPA at both the mRNA and protein levels in U87, U251 and H4 cells. Moreover, compared with those cocultured with control astrocytes, SH-SY5Y cells cocultured with CIRP-overexpressing astrocytes exhibited a significant increase in the expression of amyloid-β (Aβ)1-42 and the hyperphosphorylated microtubule-associated protein tau (Tau). Conclusion: CIRP overexpression inhibited the expression of uPA in human astrocytes, which promoted the expression of Aβ1‒42 and the phosphorylation of tau in neurons, thus increasing the risk of AD. These results suggest that the overexpression of CIRP in astrocytes contributes to the development of AD.