Identifying receptors for neuropeptides and peptide hormones: challenges and recent progress

Intercellular signaling events mediated by neuropeptides and peptide hormones represent important targets for both basic science and drug discovery. For many bioactive peptides, the protein receptors that transmit information across the receiving cell membrane are not known, severely limiting these signaling pathways as potential therapeutic targets. Identifying the receptor(s) for a given peptide of interest is complicated by several factors. Most notably, cell-cell signaling peptides are generated through dynamic biosynthetic pathways, can act on many different families of receptor proteins, and can participate in complex ligand-receptor interactions that extend beyond a simple one-to-one archetype. Here, we discuss recent methodological advances to identify signaling partners for bioactive peptides. Recent advancements have centered on methods to identify candidate receptors via transcript expression, methods to match peptide- peptidereceptor pairs through high throughput screening, and methods to capture direct ligand-receptor interactions using chemical probes. Future applications of the receptor identification approaches discussed here, as well as technical advancements to address their limitations, promises to lead to a greater understanding of how cells communicate to deliver complex physiologies. Importantly, such advancements will likely provide novel targets for treatment of a number of human diseases within the central nervous and endocrine systems

Peptidomics analysis reveals changes in small urinary peptides in patients with interstitial cystitis/bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic and debilitating pain disorder of the bladder and urinary tract with poorly understood etiology. A definitive diagnosis of IC/BPS can be challenging because many symptoms are shared with other urological disorders. An analysis of urine presents an attractive and non-invasive resource for monitoring and diagnosing IC/BPS. The antiproliferative factor (APF) peptide has been previously identified in the urine of IC/BPS patients and is a proposed biomarker for the disorder. Nevertheless, other small urinary peptides have remained uninvestigated in IC/BPS primarily because protein biomarker discovery efforts employ protocols that remove small endogenous peptides. The purpose of this study is to investigate the profile of endogenous peptides in IC/BPS patient urine, with the goal of identifying putative peptide biomarkers. Here, a non-targeted peptidomics analysis of urine samples collected from IC/BPS patients were compared to urine samples from asymptomatic controls. Our results show a general increase in the abundance of urinary peptides in IC/BPS patients, which is consistent with an increase in inflammation and protease activity characteristic of this disorder. In total, 71 peptides generated from 39 different proteins were found to be significantly altered in IC/BPS. Five urinary peptides with high variable importance in projection (VIP) coefficients were found to reliably differentiate IC/ BPS from healthy controls by receiver operating characteristic (ROC) analysis. In parallel, we also developed a targeted multiple reaction monitoring method to quantify the relative abundance of the APF peptide from patient urine samples. Although the APF peptide was found in moderately higher abundance in IC/BPS relative to control urine, our results show that the APF peptide was inconsistently present in urine, suggesting that its utility as a sole biomarker of IC/BPS may be limited. Overall, our results revealed new insights into the profile of urinary peptides in IC/BPS that will aid in future biomarker discovery and validation efforts

Peptidomics analysis reveals changes in small urinary peptides in patients with interstitial cystitis/bladder pain syndrome

Interstitial cystitis or bladder pain syndrome (IC/BPS) is a chronic and debilitating pain disorder of the bladder and urinary tract with poorly understood etiology. Symptomatic criteria to aid in the diagnosis of IC/BPS includes bladder pain, an increase in urinary urgency or Hunner’s ulcers on the bladder wall. Our study revealed differences in the profiles of small urinary peptides for IC/BPS patients compared to age-matched controls which is consistent with increased protease activity in IC/BPS. Our study also enabled the direct measurement of APF peptide abundance in IC/BPS and control urine. Our results indicate that the full-length APF peptide was not consistently found in the urine of IC/BPS patients at levels sufficient to reliably differentiate IC/BPS patients from healthy individuals