Fluorescence-Based Multiplex Western Blot to Simultaneously Detect the Insulin-Like Growth Factor-1 (IGF-1) Isoforms

: Insulin-like growth factor-1 (IGF-1) is critical for tissue growth and development. The IGF-1 gene contains six exons and due to alternative splicing three different isoforms might be produced: the IGF-1Ea, Eb, and Ec prohormones (proIGF-1s). These proIGF-1s share the same IGF-1 mature sequence, which is responsible for the IGF-1 receptor binding but differ in their carboxy-terminal extensions called Ea-, Eb-, and Ec-peptides. Several lines of evidence indicate that E-peptides control the intracellular proIGF-1s localization and maturation. Here, we present a multiplex Western blotting system able to simultaneously discriminate and quantify mature IGF-1, proIGF-1s and E-peptides within the same sample. HEK293 cells were transiently transfected with plasmids containing the IGF-1Ea, IGF-1Eb, or IGF-1Ec isoform or an empty vector. Two different primary antibodies, which recognize the mature sequence or the common region of E-peptides, were used to detect IGF-1 isoforms, which were subsequently distinguished with secondary antibodies conjugated to different fluorophores. Our results demonstrate the feasibility of simultaneously detecting different IGF-1 isoforms using two primary antibodies directed against different epitopes of proIGF-1s, combined with fluorescence-conjugated secondary antibodies. Furthermore, this dual-epitope strategy increases the specificity of protein detection, making it a valuable tool for studying the diverse roles of IGF-1 isoforms in biological processes.