To address this objective, we first used a set of integrative approaches combining data on human transcriptomics, genomics, proteomics, receptor sequence and structure, and molecular pharmacology to analyse how the tissue-specific expression of structurally and functionally diverse versions of the same receptor, in the form of GPCR protein isoforms, could contribute to differential signalling responses. Our results, which have been disseminated in conference presentations, through a high impact publication (Marti-Solano et al, Nature 2020), in the form of a dedicated press release (see link below) and via the deposition of our data in a web resource hosted by the widely used GPCR database in collaboration with researchers at the University of Copenhagen (gpcrdb.org/protein/isoforms) revealed that 38% of the GPCRs expressed in 30 different human tissues had two or more isoforms. Importantly, these isoforms displayed structural diversity in key receptor regions tasked with signal recognition (the N-terminal segment) and receptor signalling transmission and localisation (the C-terminal segment). Structural comparison between isoforms that had been functionally interrogated in the literature and previously uncharacterised isoforms also allowed proposing how variation in particular receptor regions could result in specific receptor signalling outcomes. Besides that, considering combinatorial expression of receptor isoforms across human tissues allowed determining which receptors could present a higher degree of functional diversity when exposed to a systemically-distributed signal or drug. Furthermore, this analysis also allowed detecting structurally diverse receptor isoforms with differential tissue distribution. This could open new opportunities for the development of next-generation isoform-specific GPCR drugs with an increased tissue selectivity that would be devoid of unwanted side effects in other unintended sites of action. In this line, external experimental collaborators at the universities of Michigan, Cambridge and Glasgow pharmacologically characterised the signalling properties of different receptor isoforms of pharmaceutical interest and validated our observations of signal diversification via the combinatorial expression of receptor isoforms in different cell systems. Importantly, during the timeline of the project, our data-driven methods also allowed us to analyse other sources of GPCR functional diversity related to the effects of rare variants found in the general population on receptor structure and signalling (Brouwers et al, Cell Rep 2021) and to changes in receptor abundance related to age and sex differences (manuscript in preparation).
