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Hypoxic pulmonary hypertension (HPH) is characterized by progressive pulmonary vasoconstriction, vascular remodeling, and right ventricular hypertrophy, causing right heart failure. This study aimed to investigate the therapeutic effects of exosomes from Tibetan umbilical cord mesenchymal stem cells on HPH via the TGF-β1/Smad2/3 pathway, comparing them with exosomes from Han Chinese individuals. An HPH rat model was established in vivo, and a hypoxia-induced injury in the rat pulmonary artery smooth muscle cells (rPASMCs) was simulated in vitro. Exosomes from human umbilical cord mesenchymal stem cells were administered to HPH model rats or added to cultured rPASMCs. The therapeutic effects of Tibetan-mesenchymal stem cell-derived exosomes (Tibetan-MSC-exo) and Han-mesenchymal stem cell-derived exosomes (Han-MSC-exo) on HPH were investigated through immunohistochemistry, western blotting, EdU, and Transwell assays. The results showed that Tibetan-MSC-exo significantly attenuated pulmonary vascular remodeling and right ventricular hypertrophy in HPH rats compared with Han-MSC-exo. Tibetan-MSC-exo demonstrated better inhibition of hypoxia-induced rPASMCs proliferation and migration. Transcriptome sequencing revealed upregulated genes (Nbl1, Id2, Smad6, and Ltbp1) related to the TGFβ pathway. Nbl1 knockdown enhanced hypoxia-induced rPASMCs proliferation and migration, reversing Tibetan-MSC-exo-induced downregulation of TGFβ1 and p-Smad2/3. Furthermore, TGFβ1 overexpression hindered the therapeutic effects of Tibetan-MSC-exo and Han-MSC-exo on hypoxic injury. These findings suggest that Tibetan-MSC-exo favors HPH treatment better than Han-MSC-exo, possibly through the modulation of the TGFβ1/Smad2/3 pathway via Nbl1., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

AIM: To investigate the effect of hypoxia-preconditioned human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-Exos) on pulmonary vascular endothelial-mesenchymal transition (EndMT) in hypoxic pulmonary hypertension (HPH). METHODS: (l) Primary hUCMSCs were isolated and cultured by tissue adhesion method, and hUCMSC-Exos were extracted by ultrafiltration and identified. (2) Twenty-four SPF male SD rats were randomly divided into normoxia (N) group, hypoxia (H) group, hypoxia+normoxic hUCMSC-Exos group and hypoxia+hypoxia-preconditioned hUCMSC-Exos group, with 6 rats in each group. The rats in H group and intervention groups were placed in a cabin that simulated the hypoxic environment at an altitude of 5 000 m, and normoxic hUCMSC-Exos, hypoxia-precon-ditioned hUCMSC-Exos or equivalent volume of PBS were injected through the tail vein on the 3rd, 5th, 7th, 10th and 14th days in hypoxia environment. After 21 d of modeling, the right ventricular systolic pressure (RVSP) and right ventricular hypertrophy index (RVHI) of the rats were detected, and the pathological changes of lung tissues were observed by HE staining. (3) After starvation for 12 h, human pulmonary arteriole endothelial cells (HPAECs) were randomly divided into normoxic control (N-Con) group, hypoxic model (H-Con) group, hypoxia+normoxic hUCMSC-Exos group and hypoxia+hypoxia-preconditioned hUCMSC-Exos group. The migration ability and tube formation ability of HPAECs were detected by Transwell assay and tube formation experiment. The expression of CD31 and α-smooth muscle actin (α-SMA) in HPAECs was detected by immunofluorescence double-staining. The protein levels of CD31, VE-cadherin, α-SMA and vimentin in pulmonary vessels and HPAECs were assessed by Western blot. RESULTS: (1) The HPH rat model was successfully established after 21 d of hypoxia, and EndMT occurred in pulmonary vessels. Compared with N group, the levels of RVSP, RVHI, percentage of vascular wall area (WA%) and percentage of vascular wall thickness (WT%) in H group were significantly increased (P<0.01), pulmonary vascular wall thickening and the protein levels of CD31 and VE-cadherin were significantly decreased (P<0. 01), while the protein levels of α-SMA and vimentin were significantly increased in pulmonary vessels (P<0.05 or P<0.01). Compared with H group, the RVSP, RVHI, WA% and WT% (P<0.01) were significantly decreased (P<0.05 or P<0.01), and pulmonary vascular remodeling was attenuated after normoxic or hypoxia-preconditioned hUCMSC-Exos intervention. After hypoxia-preconditioned hUCMSC-Exos intervention, HPH pul-monary vascular remodeling and EndMT formation were significantly inhibited. (2) After 48 h of hypoxic treatment, the migration, tubule formation and EndMT of HPAECs were induced. Compared with H-Con group, cell migration and tube formation were significantly decreased after hypoxia-preconditioned hUCMSC-Exos intervention (P<0. 01). The protein levels of CD31 and VE-cadherin were increased, while the protein levels of α-SMA and vimentin were decreased (P<0.05 or P<0.01). CONCLUSION: Hypoxia-preconditioned hUCMSC-Exos attenuate the formation of HPH pulmonary vascular remodeling by inhibiting pulmonary vascular EndMT. [ABSTRACT FROM AUTHOR]