Study of the insulin-like peptide 3 in human platelets

The insulin-like 3 peptide (INSL3) is autocrine/paracrine insulin-related hormone with a size of approximately 6kDa [1]. It mediates through a leucine rich G-coupled receptor named LGR8. INSL3 is mainly expressed in human Leydig cells and is directly responsible for migration of the testis during the pre-natal period in male development. [2] INSL3 mRNA has recently been verified in human platelets whereas no mRNA has been detected for LGR8 (by Sanofi-Aventis GmbH in Frankfurt, Germany), indicating that INSL3 might be released through paracrine functions at sites of platelet adhesion and aggregation upon a vascular injury. Furthermore, has activated platelets been shown to translate essential proteins upon activation, in a term called “signal-dependent protein synthesis”. The B-Cell lymphoma-3 protein (BCL-3) is an example of such a protein [3], and there is a possibility that INSL3 might be also. In this thesis we wanted to detect the relaxinlike peptide 3 hormone (INSL3). (Its function, location and the timeframe of its release, when/if it is secreated in stimulated platelets). The source of platelet-derived INSL3 can be found with western blotting and enzyme immunoassay. Detection of the insulin-like 3 peptide in human platelets turned out to be a difficult challenge due to the small amount of INSL3 secretion upon platelet activation; hence the total amount of INSL3 produced might be below detection limit.