Reviewing the physiological roles of the novel hormone-receptor pair INSL5-RXFP4: a protective energy sensor?

There is no common consensus on the physiological role of insulin-like peptide 5 (INSL5) and its cognate receptor, relaxin family peptide receptor 4 (RXFP4). The experimental data for INSL5-RXFP4 expression and function point to a potential role of the peptide hormone and receptor pair in linking energy availability, homeostasis, and inflammation. In this review, we summarize studies on the INSL5-RXFP4 system and propose that the current findings from diverse experimental settings point broadly to a role as a protective energy sensor (PES).