IRAK-M deficiency exacerbates dopaminergic neuronal damage in a mouse model of sub-acute Parkinson's disease

Emerging evidence has proved that inflammatory responses aggravate the pathological progression of Parkinson's disease. This study aimed to identify the role of Interleukin-1 receptor-associated kinase-M (IRAK-M) as an important negative regulator of innate immunity, in the pathological progression of Parkinson's disease. In the present study, a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection was administered to prepare the acute and sub-acute Parkinson's disease mouse models. Western blot analysis was utilized to examine the protein expressions of tyrosine hydroxylase and IRAK-M. The mRNA expression levels of IRAK-M, interleukin (IL)-6, IL-β, and cyclooxygenase-2 were evaluated via using reverse transcription quantitative PCR (RT-qPCR). The expression of tyrosine hydroxylase-positive neurons in corpus striatum and substantia nigra pars compacta (SNc) tissues was detected using immunohistochemistry. The results showed that the protein and mRNA levels of IRAK-M were considerably upregulated in corpus striatum and SNc tissues in the sub-acute Parkinson's disease model. Furthermore, IRAK-M knockout significantly enhanced the MPTP-induced loss of tyrosine hydroxylase-positive fibers in corpus striatum and tyrosine hydroxylase-positive neurons in SNc, and intensified the effect of MPTP on the activation of microglial cells and the expression of inflammatory cytokines. In addition, sub-acute Parkinson's disease mice with IRAK-M deletion exhibited worse motor abilities than those of wild-type littermates. Overall, the present study suggested that IRAK-M reduces dopaminergic neuron damage in sub-acute Parkinson's disease by suppressing inflammation, which may provide a new therapeutic target for Parkinson's disease treatment.