I-tRF-Asp promotes vascular remodeling in hypoxic pulmonary hypertension via hnRNPU phase separation which affects TCF7L2 alternative splicing.

These models employed antisense oligonucleotide inhibitor and adeno-associated virus-mediated silencing. The underlying mechanisms were further explored via RNA immunoprecipitation, liquid-liquid phase separation assays, cell proliferation assessment, western blot, alternative splicing profiling and molecular dynamics simulation. RESULTS: Inhibition of i-tRF-Asp ameliorated hypoxia-induced pulmonary vascular remodeling, primarily through suppressing excessive proliferation of mPASMCs.

Further analysis indicated that i-tRF-Asp facilitates liquid–liquid phase separation (LLPS) of hnRNPU. This process mediates selective recruitment of Tcf7l2 pre-mRNA and promotes alternative splicing, resulting in a pro-proliferative Tcf7l2 transcript variant that drives mPASMC proliferation. Furthermore, we have identified that the endonuclease ERN1 can upregulate the expression of i-tRF-Asp.

CONCLUSION: The endoribonuclease ERN1 upregulates the expression of i-tRF-Asp, which in turn facilitates mPASMC proliferation and pulmonary vascular remodeling. This process is driven by hnRNPU LLPS-dependent alternative splicing of the long Tcf7l2 transcript isoform.