The cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS)-cyclic GMP-AMP (cGAMP)-stimulator of interferon genes (STING) pathway mediates antiviral innate immunity upon sensing cytosolic DNA. Here, we examined the impact of sphingomyelin phosphodiesterase acid-like 3B (SMPDL3B), a paralog of the LXR lipid metabolism-induced cGAMP-degrading enzyme SMPDL3A, on viral infection. We found that SMPDL3B was induced and stabilized by both viral infection and membrane-disturbing agents, suggesting a role in sensing membrane stress as an early signal of cellular danger. Deletion of SMPDL3B impaired DNA virus infection. Upon induction, SMPDL3B suppressed cGAS-STING signaling and downstream transcriptional pathways, including the interferon response. Mechanistically, SMPDL3B functioned as a cGAMP hydrolase; cGAMP-induced SMPDL3B dimerization enabled its hydrolase activity and a negative feedback loop that dampened STING signaling. SMPDL3B-deficient cells had elevated cGAMP concentrations, and Smpdl3b −/− mice exhibited enhanced cGAMP accumulation, heightened immune activation, and reduced viral loads upon herpes simplex virus type 1 (HSV-1) infection. Thus, SMPDL3B links membrane stress to modulation of cGAS-STING signaling through cGAMP degradation, with potential implications in the contexts of inflammation or autoimmunity.
Abnormal inflammation of vascular endothelial cells occurs frequently in diabetic retinopathy (DR). Sphingomyelin phosphodiesterase acid-like 3B (SMPDL3B) is a lipid raft enzyme and plays an anti-inflammatory role in various diseases but its function in DR-related vascular endothelial dysfunction remains unknown. We first found that SMPDL3B expression was upregulated from week 10 to 18 in the retinal tissues of db/db mice. Particularly, the high expression of SMPDL3B was mainly observed in retinal vascular endothelium of DR mice. To interfere retinal SMPDL3B expression, adeno-associated viruses 2 (AAV-2) containing SMPDL3B specific shRNA (1233–1253 bp) were injected into the vitreous cavity of db/db mice. SMPDL3B silencing exacerbated the spontaneous DR by further activating the NF-κB/NLRP3 pro-inflammatory pathway. In vitro , human retinal microvascular endothelial cells (HRVECs) were infected with SMPDL3B-shRNA lentiviruses and then stimulated with 30 mM glucose (HG) for 24 h. SMPDL3B-silenced HRVECs secreted more interleukin-1β and had enhanced nuclear p65 translocation. Notably, HG treatment induced the palmitoylation of SMPDL3B. Zinc finger DHHC-type palmitoyltransferase 5 (ZDHHC5) is a palmitoyltransferase that catalyzes the palmitoylation of its substrates, HG exposure increased the interaction between ZDHHC5 and SMPDL3B in HRVECs. 2-BP, a palmitoylation inhibitor, accelerated the protein degradation of SMPDL3B, whereas palmostatin B, a depalmitoylation inhibitor, decreased its turnover rate in HRVECs. Collectively, the present study suggests a compensatory increase of SMPDL3B in HG-treated HRVECs and the retinal tissues of DR mice, indicating that SMPDL3B may be a potential target for DR treatment.
危险品化学品经营许可证（带存储）