Exploring the function of mammalian Adenosine Deaminase 2, a novel anti-inflammatory glycoprotein of the macrophage lysosome

Abstract

Deficiency of Adenosine Deaminase 2 (DADA2) is an autosomal recessive autoinflammatory disease currently standing without sufficient treatment. The main reason for the lack of targeted therapy is the lack of understanding the protein's function, resulting in only symptomatic, anti-inflammatory treatments. This thesis aims to contribute to the research, which can, ultimately, be used to develop a therapy for DADA2 patients. The predominant hypothesis on the molecular function of ADA2 is that it is a secreted N-glycosylated protein produced in monocytes/macrophages and hydrolyzes plasmic Adenosine (Ado) to Inosine (Ino). A novel theory considering this, is that ADA2 is a lysosomal protein regulating DNA at acidic pH. DNA, like Ado, is highly pro-inflammatory and could also cause the symptoms seen in DADA2 patients. Large evolutionary differences are visible, such as a complete gene deletion from rodents and large variations in affinity for Ado. To gain more insight into the differences between species, ADA2 from chicken liver and sheep spleen was partially purified and analyzed with MS/MS. Enzyme assays testing heat stability and specific activity were also conducted. In conclusion, this thesis' results suggest an evolutionary drift in ADA2's function, from hydrolysis of free Ado in invertebrates to the larger substrate DNA in vertebrates. Some mammals, such as pigs and humans, where ADA2 is promoted in monocytes/macrophages, might be attributed to ADA2 functioning as a regulator of lysosomal DNA in highly stressed macrophages and avoiding critical DNA concentrations causing inflammation.