Deficient FANCL Predisposes to Endothelial Damage: A New Therapeutic Target for Pulmonary Hypertension

<b>Rationale:</b> Clinical observations have suggested an association between alkylating agent-based chemotherapy and pulmonary arterial hypertension (PAH). The Fanconi anemia (FA) pathway, the principal mechanism for resolving alkylating agent-induced DNA damage, has been implicated in this process. <b>Objectives:</b> To establish the interplay among the FA pathway, DNA damage, and PAH. <b>Methods:</b> A knockout-first mouse model for FA complementation group L (<i>Fancl</i>^kf/kf) and an adenovirus-associated virus 9-mediated <i>Fancl</i> overexpression (AAV-<i>Fancl</i>) model were used. Lung specimens, pulmonary arterial endothelial cells from patients with PAH, and primarily cultured pulmonary microvascular endothelial cells (PMVECs) from wild-type and <i>Fancl</i>^kf/kf mice were analyzed. <b>Measurements and Main Results:</b> Data analysis on lung single-cell RNA-sequencing datasets revealed significant downregulation of <i>FANCL</i> in endothelial cells from patients with idiopathic PAH, a finding consistently validated in both clinical samples (lung specimens and pulmonary arterial endothelial cells) and the monocrotaline-induced PAH rat model. Notably, <i>Fancl</i>^kf/kf mice developed spontaneous PAH and showed heightened susceptibility to alkylating agent (mitomycin C)-induced PAH, characterized by severe DNA damage and apoptosis in PMVECs. These pathological phenotypes were rescued through <i>Fancl</i> gene supplementation via AAV-<i>Fancl</i> or pharmacological intervention with the DNA damage protector amifostine. Mechanistically, transcriptomic profiling combined with functional validation demonstrated a suppressed bone morphogenetic protein signaling coupled with hyperactivated transforming growth factor-β pathways in PMVECs from <i>Fancl</i>^kf/kf mice. Importantly, this imbalance was fully restored in PMVECs from AAV-<i>Fancl</i>-treated mice. <b>Conclusions:</b> Deficient <i>Fancl</i> plays a key role to promote PAH, and targeted rescue of <i>Fancl</i> could be a novel effective strategy for the treatment of PAH.