Review papers with raw data transparency

Concise appraisal

The preprint reports that an NTRK2 isoform switch (loss of full-length NTRK2 FL and gain of truncated NTRK2 T1) in general capillary endothelial cells associates with failed vascular regeneration in bronchopulmonary dysplasia and that lipid nanoparticle delivered NTRK2 FL mRNA restores angiogenesis and alveologenesis in organoid and mouse models (NTRK2 Isoform BPD Preprint

Paper Review Isoform-Specific Roles of NTRK2 in Pulmonary Vascular Regeneration

Executive summary

This preprint integrates human multiomic single-cell and spatial data with iPSC-derived vessel organoids and mouse hyperoxia and hindlimb ischemia models to argue that an NTRK2 isoform switch (NTRK2-FL versus truncated NTRK2-T1) controls capillary endothelial regenerative capacity in bronchopulmonary dysplasia (BPD) and that restoring NTRK2-FL via lipid nanoparticle mRNA rescues vascular regeneration (NTRK2 Isoform BPD Preprint

Strengths of the study

• Human relevance: analysis uses multiome single-cell profiling and spatial transcriptomics from human BPD lungs (primary human tissue) rather than only rodent models, increasing clinical relevance (Human multiome and organoid integration
• Isoform resolution: the paper separates reads that map to the shared ectodomain versus the tyrosine kinase domain and validates with isoform-specific RNA scope and antibodies, directly addressing isoform-level biology (Isoform read mapping and antibody validation
• Functional tests across systems: iPSC vessel organoids, HPMVEC in vitro assays, BPD-like mouse hyperoxia and hindlimb ischemia models, and LNP mRNA therapeutics provide cross-model validation of phenotype and intervention (Cross model functional validation

Major weaknesses and limitations

1. Small human sample size and sampling bias: the methods indicate n=3 BPD and n=2 control lungs for multiome profiling and a small number of spatial samples; with n that small patient heterogeneity and stratification (severity, postnatal age, comorbidities) can bias results and overstate generality (Human sample sizes and ages
2. Causality versus association: while overexpression of NTRK2-T1 produces maladaptive phenotypes and NTRK2-FL mRNA rescues, the mechanisms linking isoform balance to downstream signaling and in vivo disease trajectories remain incompletely proven; genetic loss/gain within endogenous regulation (e.g., CRISPR isoform-specific knockin/knockout) is not fully shown to exclude off-target or overexpression artefacts (mRNA overexpression functional assays
3. Therapeutic durability and safety unknown: single-course LNP mRNA rescue in neonatal mice and hindlimb ischemia are promising, but durability, immune responses, endothelial tropism specificity, dose range/toxicity, and off-target effects (especially neuronal NTRK2 expression) need formal evaluation before translational claims (LNP mRNA therapy results and caveats
4. Isoform detection sensitivity: isoform quantification via short-read mapping to shared versus kinase domain is valid but can misassign reads if alternative splicing or partial degradation occurs; long-read RNAseq and mass-spectrometry peptide-level isoform confirmation would strengthen claims (Isoform read quantification method

Detailed evidence review and mechanistic plausibility

1) Human multiome and spatial data

The authors identify gCap-C2 endothelial cells expanded in BPD with elevated NTRK2 reads mapping predominantly to the shared extracellular domain but not the tyrosine kinase domain, consistent with increased truncated NTRK2-T1 in severe BPD. They perform cell2location deconvolution and CellChat ligand-receptor colocalization analysis to argue altered intercellular signaling networks (CellChat and spatial colocalization approach

2) Isoform biology and signaling

The paper reports that NTRK2-FL supports canonical BDNF-TrkB signaling (ERK/AKT phosphorylation) in ECs, whereas NTRK2-T1 promotes RhoA activation and dysregulated calcium signaling and suppresses ERK/AKT phosphorylation, producing impaired proliferation, barrier dysfunction, and angiogenesis. This mechanistic divergence is plausible because TrkB-T1 isoforms lack the intracellular tyrosine kinase and can act as dominant negatives or trigger alternative signaling through scaffolds and GTPase modulators; the preprint shows in vitro experiments where BDNF causes RhoA activation in NTRK2-T1 expressing ECs and abolishes ERK/AKT phosphorylation (Isoform-specific downstream signaling

3) Splicing regulation

The authors implicate a HOXA5 transcriptional axis and RBFOX2 as a splicing regulator shifting NTRK2 FL to T1. They present RNA immunoprecipitation showing RBFOX2 binds intron 15-16 of NTRK2 pre-mRNA and RBFOX2 overexpression increases T1/FL ratio in ECs (RBFOX2 splicing of NTRK2

Reproducibility, methods transparency, and data availability

The authors state processed 10x multiome and Visium data are on GitHub and raw data will be submitted to dbGaP/GEO; methods mention Seurat, Cell Ranger, CellChat and cell2location and detail RNA-scope probes and antibodies used. These are necessary for reproducibility; long-read RNAseq and proteomic peptide-level isoform confirmation are not reported and would improve reproducibility and certainty (Data availability statement

Counterpoints and alternative explanations

• Elevated NTRK2 Pan signal in BPD could reflect increased cell-surface receptor shedding, truncated transcripts from alternative promoters, or cell composition shifts rather than splicing alone; long-read seq would disambiguate (Isoform read counting approach
• BDNF ligand levels reportedly remain unchanged; therefore, receptor dysfunction (isoform) is plausible, but ligand compartmentalization or posttranslational ligand alterations could still modulate signaling (BDNF unchanged in BPD

Practical/ translational considerations

LNP-mRNA rescue of NTRK2-FL is an innovative translational angle. Key preclinical translational gaps include: endothelial cell-specific delivery and biodistribution in neonates, immunogenicity of repeated dosing, off-target neuronal TrkB activation with potential neurobehavioral effects, and long-term structural/functional durability; the preprint notes the need for additional studies and acknowledges limitations (Therapeutic caveats and need for validation

Suggested experiments to strengthen claims

1. Long-read RNA sequencing (PacBio/ONT) of human BPD endothelial isolates and organoids to map full-length NTRK2 isoforms and quantify transcript structure.
2. Isoform-specific genetic perturbation using CRISPR exon/intron editing to force endogenous isoform expression ratios in ECs (isoform swap), then test regeneration in organoids and mouse models to avoid overexpression artefacts.
3. Mass-spectrometry proteomics with isoform-unique peptides from human samples and organoids to confirm protein-level isoform abundance.
4. Biodistribution, repeat-dose immunogenicity, and neurobehavioral safety studies for NTRK2-FL LNP mRNA in neonatal rodents and a large-animal model if available.

Bottom-line assessment

The manuscript presents a coherent multiomic-to-intervention story that NTRK2 isoform balance controls capillary endothelial regenerative responses in BPD and that NTRK2-FL mRNA can rescue regeneration in model systems; evidence is moderate and promising, but small human sample size, reliance on overexpression, and limited long-term safety/durability data limit immediate translational claims (Overall study conclusions