LINC00599 Promotes Pulmonary Hypertension via Liquid-Liquid Phase Separation With G3BP1 and MYH9.

BACKGROUND Pulmonary hypertension (PH) represents a significant cardiovascular disorder marked by both functional and structural alterations within the pulmonary vasculature. Long noncoding RNAs have been closely associated with PH pathogenesis and progression, particularly in vascular remodeling and cell proliferation. Nonetheless, how long noncoding RNAs interact with downstream targets to modulate PH remains unclear. METHODS The expression levels of LINC00599 were quantified in the mouse lung tissues and pulmonary arterial smooth muscle cells (PASMCs) under hypoxic conditions. The involvement of LINC00599 in PH progression and vascular remodeling was evaluated through in vivo studies. To investigate its role in human PASMC proliferation, small interfering RNA and overexpression plasmids were used. RESULTS The expression of LINC00599 is upregulated in the medial layer of pulmonary arteries in experimental PH models and hypoxic PASMCs. Administration of lentivirus-mediated shRNA targeting LINC00599 reverses hypoxic PH in murine models. Mechanistically, LINC00599 promotes PASMC proliferation by modulating stress granule formation through m6A (N6-methyladenosine) modification and facilitating liquid-liquid phase separation with MYH9 (myosin heavy chain 9), a process previously implicated in cell-cycle regulation. Furthermore, its expression is driven by a super-enhancer mediated by the transcription factor ZNF263. CONCLUSIONS This study demonstrates that LINC00599 promotes PH progression by promoting PASMC proliferation via liquid-liquid phase separation-distinct from classical long noncoding RNA mechanisms. The identification of LINC00599 as a modulator of both m6A-dependent stress granule dynamics and MYH9-mediated phase separation expands our understanding of long noncoding RNA functionality in vascular diseases. As a target in a druggable pathway, LINC00599 holds promise for PH precision medicine.