Reactome does not provide organ-specific annotation, we aim to annotate a generic (human) cell, and users can then use expression data overlay for their organ (cell, tissue) of interest through our analysis tool (select "Microarray data" for an example). 

You can also use the "Tissue Distribution" tool to see how data from the Human Protein Atlas maps to Reactome pathway space.

Documentation is at https://reactome.org/userguide/analysis

Please keep in mind that Reactome curation focuses on human, and while you can switch to one of the other species supported by our inference protocol through the drop down in the upper left area of the pathway browser, this data is inferred from human by orthology.