Relaxin H3 (human)

We have identified a novel human relaxin gene, designated H3 relaxin, and an equivalent relaxin gene in the mouse from the Celera Genomics data base. Both genes encode a putative prohormone sequence incorporating the classic two-chain, three cysteine-bonded structure of the relaxin/insulin family and, importantly, contain the RXXXRXX(I/V) motif in the B-chain that is essential for relaxin receptor binding. A peptide derived from the likely proteolytic processing of the H3 relaxin prohormone sequence was synthesized and found to possess relaxin activity in bioassays utilizing the human monocytic cell line, THP-1, that expresses the relaxin receptor. The expression of this novel relaxin gene was studied in mouse tissues using RT-PCR, where transcripts were identified with a pattern of expression distinct from that of the previously characterized mouse relaxin. The highest levels of expression were found in the brain, whereas significant expression was also observed in the spleen, thymus, lung, and ovary. Northern blotting demonstrated an approximately 1.2-kb transcript present in mouse brain poly(A) RNA but not in other tissues. These data, together with the localization of transcripts in the pars ventromedialis of the dorsal tegmental nucleus of C57BLK6J mouse brain by in situ hybridization histochemistry, suggest a new role for relaxin in neuropeptide signaling processes. Together, these studies describe a third member of the human relaxin family and its equivalent in the mouse.

Two members of the human insulin/relaxin superfamily, relaxins-2 and 3 (H2 and H3 respectively), are separated by nearly 75 years in terms of chronological identification but are both the subject of intense recent biological study. The physiological effects of H2 relaxin include vasodilatory, anti-inflammatory, extracellular matrix remodeling, and angiogenic and anti-ischemic. Because of its potent systemic and renal vasodilatory effects, it is currently undergoing phase III clinical trial for the treatment of acute heart failure. In contrast, H3 relaxin is a highly conserved neuropeptide that has rapidly emerged as an important regulator of homeostatic physiology and complex behaviors. Because of their immense clinical potential, an understanding of the structural features that control their functions is critical for rational drug design and development. The native receptor for H2 relaxin is RXFP1. It also strongly binds to the related receptor, RXFP2. The native receptor for H3 relaxin is the unrelated receptor, RXFP3; however, it also has high affinity for another related receptor, RXFP4. Interestingly, H3 relaxin also has a high affinity for RXFP1 and can interact with RXFP2 with a significantly lower affinity. H3 relaxin thus interacts with all four of the relaxin family receptors. Previous studies have shown that H2 and H3 relaxins interact with their receptors primarily using their B-chain specific residues. However, more recent studies suggest that the role of the respective A and B chains for their activity is both peptide- and receptor-dependent. This mini-review summarizes these recent findings on the structure-activity relationships of H2 and H3 relaxins.

Objectives: Calcium oxalate (CaOx) crystals can activate inflammatory cytokines by triggering inflammasomes, which cause damage to the adhered epithelium, a dysfunctional microenvironment and even renal failure. However, a comprehensive and in-depth understanding of the mechanisms underlying the effects of these crystals on damage and cytokine function in renal tubular epithelial cells (TECs) remains limited and to be explored. Materials and methods: We detected the pyroptosis of TECs induced after exposure to CaOx crystals and demonstrated the significance of cytokine activation in the subsequent inflammatory processes through a proteomic study. We then conducted animal and cell experiments to verify relevant mechanisms through morphological, protein, histological and biochemical approaches. Human serum samples were further tested to help explain the pathophysiological mechanism of H3 relaxin. Results: We verified that crystal-induced extracellular adenosine triphosphate (ATP) upregulation via the membrane purinergic 2X7 receptor (P2X7 R) promotes ROS generation and thereby activates NLRP3 inflammasome-mediated interleukin-1β/18 maturation and gasdermin D cleavage. Human recombinant relaxin-3 (H3 relaxin) can act on the transmembrane receptor RXFP1 to produce cAMP and subsequently improves crystal-derived damage via ATP consumption. Additionally, endogenous relaxin-3 was found to be elevated in patients with renal calculus and can thus serve as a biomarker. Conclusions: Our results provide previously unidentified mechanistic insights into CaOx crystal-induced inflammatory pyroptotic damage and H3 relaxin-mediated anti-inflammatory protection and thus suggest a series of potential therapeutic targets and methods for but not limited to nephrocalcinosis.