Assessment of proteins regulating retinoic acid metabolism and signaling is important for understanding cardiac development and disease, but conventional antibody-based assays face specificity and quantitation challenges. To address this, the authors implemented a targeted proteomics workflow using SureQuant internal standard–triggered parallel reaction monitoring (IS-PRM) on an Orbitrap Fusion Lumos instrument. The approach uses heavy isotope–labeled peptide internal standards to continuously monitor for targets; detection of the heavy standard triggers a high-resolution targeted MS/MS acquisition that captures spectra for both the heavy standard and the endogenous (light) peptide.
The study team designed a panel of 80 stable isotope–labeled (heavy) peptides representing proteins involved in retinoid signaling and metabolism. Peptide sequences were selected for applicability to human samples and conservation across multiple species to enable cross-species comparisons. The source abstract does not enumerate the individual proteins or peptide sequences included in the panel; those specifics were not reported in the abstract.
Initial survey experiments employed directed data-dependent acquisition on the Orbitrap Fusion Lumos to determine precursor and product ion masses for each heavy peptide. These measured masses were programmed into the SureQuant acquisition method to enable continuous monitoring. When the mass spectrometer detects the heavy internal standard signal above threshold, it automatically switches to targeted PRM acquisition mode and repeatedly acquires high-resolution MS/MS spectra for both the heavy and the corresponding endogenous peptide, increasing confidence and sensitivity for quantification.
Using this IS-PRM workflow, the investigators achieved quantification of retinoid pathway–associated proteins down to as low as 10 attomoles for selected targets. The abstract reports this attomole-level sensitivity across multiple tissues and developmental stages, indicating the method's capacity for low-abundance protein detection. The source does not provide a full table of limits of detection for all panel peptides or the variability metrics; those details were not included in the abstract.
The method was applied to multiple tissue types, including lung, liver, retinal cell lines, and cardiac tissues. These applications revealed distinct tissue-specific retinoid metabolic networks, demonstrating that the composition and abundance of retinoid pathway proteins vary by tissue. The abstract indicates differential networks were identified but does not list specific protein changes or quantitative values in the source text.
Developmental profiling was performed in mouse and rat hearts. Results indicated remodeling of retinoid pathway proteins from embryonic to postnatal and adult stages. The authors interpret this pattern as a functional transition from retinoid-driven processes during cardiac development toward systems focused on maintaining retinoid homeostasis in the mature heart. Exact protein-level trajectories, fold changes, and statistical analyses were not provided in the abstract.
The targeted proteomics IS-PRM strategy addresses several limitations of antibody-based detection: it provides peptide-level specificity, uses internal standards to improve quantitative accuracy, and offers high sensitivity for low-abundance targets. By designing peptides conserved across species, the panel enables direct cross-species comparisons that are often difficult with antibodies that lack cross-reactivity or consistent performance across species.
This summary is limited to information reported in the article abstract. The abstract does not provide the full list of proteins or peptides quantified, raw quantitative data, statistical measures of reproducibility, or detailed methods such as sample preparation, chromatography conditions, thresholds for triggering PRM, or validation experiments. Those elements may be present in the full preprint or supplementary material but were not reported in the abstract text used as the source for this rewrite.
Overall, the reported work establishes a targeted IS-PRM proteomics workflow using a conserved 80-peptide panel and internal standard triggering to enable sensitive, cross-species quantification of proteins involved in retinoid metabolism and signaling, with applications to tissue-specific profiling and developmental remodeling in the heart.