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. Author manuscript; available in PMC: 2020 May 1.
Published in final edited form as: Pharmacol Ther. 2019 Jan 29;197:153–178. doi: 10.1016/j.pharmthera.2019.01.006

TABLE 2.

QUESTIONS REGARDING RBP4 ACTIONS IN METABOLIC DISEASE IN NEED OF RESOLUTION

1. Are the actions of RBP4 dependent upon or independent of its ligand retinol?
2. What roles do circulating holo-RBP4 versus apo-RBP4 have in the disease process?
3. Do the observed effects involve circulating RBP4, or local RBP4 actions in adipose tissue, or both?
4. To what extent do methodological differences in how circulating RBP4 levels are measured account for apparent discrepancies in findings obtained from human cohorts?
5. To what extent do genetic factors influence outcomes of human studies as well as studies carried out in animal models? To what extent do genetic differences account for some of the apparent disagreement in the literature.
6. To what extent does local inflammation in adipose tissue account for observed metabolic phenotypes? Does this explain all RBP4-induced metabolic disease.
7. To what extent does RBP4 binding to its cell surface receptor STRA6 account for observed metabolic phenotypes? Does this explain all RBP4-induced metabolic disease.