Review Papers Claim by Claim

Key factual observations (each claim linked to the source)

• Experimental design: 36 mice (C57BL/6N and BALB/c; 8-week-old), grouped by strain and sex, fed, plasma collected by cardiac puncture, stored at -80°C, profiled with Olink Target 48 and Target 96 panels; final analyzed protein set = 87 after QC/cross-panel reconciliation Paper methods and QC
• Primary results: 55 proteins showed strain-dependent differences (63.2% of 87), 33 proteins showed sex-dependent differences (37.9%); 26 proteins were strain-differential in both sexes; 10 sex-differential proteins common to both strains Paper results summary
• Conserved signals with humans: LPL and GHRL reported as female-elevated in mouse plasma and supported by human GTEx (LPL mRNA higher in subcutaneous adipose of women) and a longitudinal human plasma Olink dataset (female > male) — authors use this to argue potential conserved sex biases in energy/lipid metabolism Mouse-human concordance: LPL, GHRL

Critical appraisal — strengths

• Focused, hypothesis-aware experimental design targeting sex and strain as variables in widely used mouse lines; balanced sex and strain groups (n=9 each) improves internal comparability Study design and compliance
• Use of Olink proximity-extension assays gives sensitive, reproducible NPX readouts enabling cross-species comparisons to Human Protein Atlas/GTEx where available Olink NPX & cross-species data

Critical appraisal — limitations, biases, and blindspots

1. Limited proteome coverage: final analysis uses 87 targets drawn from two targeted Olink panels (48 + 96). This targeted approach will miss many plasma proteins (low and high abundance) and biases findings toward panel design; general claims about the plasma proteome should be qualified (panel-limited). Support: paper states panels and 87 final targets Panel-limited coverage acknowledged
2. Single age / single physiological state: all mice were 8 weeks old and fed; age and disease states are not sampled. Sex differences can be age- and hormonal-state dependent (e.g., puberty, estrous cycle, aging). Paper acknowledges this limitation Single-age limitation
3. Statistical approach & multiple testing: the paper reports proteins with P<0.05 using two-way ANOVA but does not report FDR or multiple-testing correction per protein list in the provided text. With 87 tests, a nominal P<0.05 yields ~4–5 expected false positives. This raises risk of type I errors unless corrected or validated. The methods section indicates two-way ANOVA and P<0.05 threshold but no explicit FDR statement in the provided text Statistics: two-way ANOVA, P<0.05
4. Batch/vendor effects and panel processing: two panels were processed by DNA Link Inc. or Macrogen Inc. Cross-vendor processing can introduce batch effects; while authors correlated overlapping targets and selected four with consistent correlations, full batch adjustment is not described in the accessible text. This leaves possible confounding by vendor/batch Panel/vendor processing
5. Biological confounders (feeding, circadian, estrous cycle): mice were in fed state at collection. LPL and GHRL are feeding- and circadian-sensitive; time-of-day and fasting state can substantially change circulating levels. Authors note feeding status issues for some proteins but do not report time-of-day or estrous staging Feeding/circadian confounders
6. Data availability / reproducibility: the data are available on request from corresponding authors but not deposited in a public repository in the accessible text. This reduces immediate reproducibility and independent reanalysis; the paper’s Data Availability note states data available upon reasonable request Data available on request

Practical takeaways & how convincing the main claims are

• The empirical claim that targeted plasma proteomics detects widespread sex- and strain-related differences within the tested 87 proteins is supported by the reported counts (55 strain-differential, 33 sex-differential) — but the strength of individual protein claims depends on multiple-testing control and independent replication Differential protein counts
• The cross-species concordance for LPL and GHRL (female > male) is interesting and plausible mechanistically (lipid and appetite regulators), but is correlative: external validation in independent mouse cohorts, fasting vs fed states, and larger human cohorts with covariates would be needed to elevate confidence from moderate to strong LPL/GHRL cross-species concordance

Concrete recommendations to strengthen the study (for authors or replications)

1. Deposit full NPX data matrix and sample metadata (strain, sex, exact time-of-day, fed/fasted, batch/vendor, plate IDs) into a public repository (PRIDE/Zenodo) to enable reanalysis and multiple-testing control.
2. Apply and report multiple-testing correction (e.g., Benjamini-Hochberg) or use mixed models with explicit batch factors; provide effect sizes (fold-change + CI) together with P-values.
3. Validate top hits (e.g., LPL, GHRL, TPP1, PDCD1LG2) with orthogonal assays (ELISA, targeted MS) in independent cohorts including fasting-time controls and multiple ages.
4. Test estrous cycle phase in females or standardize collection timing and report circadian timing; ideally add fasted vs fed comparisons for appetite/lipid-related proteins.
5. Extend to more strains and ages (e.g., older mice) and to disease models to gauge generality and translational relevance.

Novel hypotheses & experimental ideas (testable)

1. Hypothesis A: Female-biased plasma LPL reflects increased subcutaneous adipose LPL expression/activity that contributes to sex-dimorphic adipose lipid partitioning; test by measuring tissue LPL mRNA/protein and post-heparin LPL activity in matched male/female mice across fasting states and strains.
2. Hypothesis B: Elevated female plasma GHRL (ghrelin) reflects sex-specific gastric ghrelin secretion rhythms; test by serial sampling across circadian cycle and by stomach mucosal ghrelin expression, and test feeding-response kinetics by standardized meal challenge.

What would falsify the main conclusions?

• If independent, well-powered replication cohorts (multiple labs) with full panel coverage and appropriate corrections fail to reproduce the sex- or strain-differential proteins (particularly LPL/GHRL), the paper’s claim about conserved sex-biased plasma proteins would be weakened.
• If controlling for feeding status and circadian time removes the female > male differences for LPL/GHRL, that would indicate the observed biases are state-dependent rather than constitutive sex differences.