Search Results

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). Specifically, we review the evidence that (1) INSL5–RXFP4 could regulate immune response by decreasing the production of proinflammatory cytokines and may be involved in the stress response via the HPA axis; (2) INSL5–RXFP4 may signal through sensory neurons on the vagus nerve, transmitting signals to the CNS; and (3) INSL5–RXFP4 could have local autocrine/paracrine roles within the intestinal tract and immune cells. Further investigation and clarification of these proposed roles of INSL5–RXFP4 may prove a greater physiological relevance for the pair and add to existing evidence of INSL5–RXFP4 role as a PES.