Long noncoding RNA SNHG16 regulates TLR4-mediated autophagy and NETosis formation in alveolar hemorrhage associated with systemic lupus erythematosus

Abstract

Background: Dysregulated long noncoding RNA (lncRNA) expression with increased apoptosis has been demonstrated in systemic lupus erythematosus (SLE) patients with alveolar hemorrhage (AH). SNHG16, a lncRNA, can enhance pulmonary inflammation by sponging microRNAs, and upregulate toll-like receptor 4 (TLR4) expression via stabilizing its mRNAs. TRAF6, a TLR4 downstream signal transducer, can induce autophagy and NETosis formation. In this study, we investigated whether SNHG16 could regulate TLR4-mediated autophagy and NETosis formation in SLE-associated AH.

Methods: Expression of SNHG16, TLR4 and TRAF6 and cell death processes were examined in lung tissues and peripheral blood (PB) leukocytes from AH patients associated with SLE and other autoimmune diseases, and in the lungs and spleen from a pristane-induced C57BL/6 mouse AH model. SNHG16-overexpressed or -silenced alveolar and myelocytic cells were stimulated with lipopolysaccharide (LPS), a TLR4 agonist, for analyzing autophagy and NETosis, respectively. Pristane-injected mice received the intra-pulmonary delivery of lentivirus (LV)-SNHG16 for overexpression and prophylactic/therapeutic infusion of short hairpin RNA (shRNA) targeting SNHG16 to evaluate the effects on AH. Renal SNHG16 expression was also examined in lupus nephritis (LN) patients and a pristane-induced BALB/c mouse LN model.

Results: Up-regulated SNHG16, TLR4 and TRAF6 expression with increased autophagy and NETosis was demonstrated in the SLE-AH lungs. In such patients, up-regulated SNHG16, TLR4 and TRAF6 expression was found in PB mononuclear cells with increased autophagy and in PB neutrophils with increased NETosis. There were up-regulated TLR4 expression and increased LPS-induced autophagy and NETosis in SNHG16-overexpressed cells, while down-regulated TLR4 expression and decreased LPS-induced autophagy and NETosis in SNHG16-silenced cells. Pristane-injected lung tissues had up-regulated SNHG16, TLR4/TRAF6 levels and increased in situ autophagy and NETosis formation. Intra-pulmonary LV-SNHG16 delivery enhanced AH through up-regulating TLR4/TRAF6 expression with increased cell death processes, while intra-pulmonary prophylactic and early therapeutic sh-SNHG16 delivery suppressed AH by down-regulating TLR4/TRAF6 expression with reduced such processes. In addition, there was decreased renal SNHG16 expression in LN patients and mice.

Conclusions: Our results demonstrate that lncRNA SNHG16 regulates TLR4-mediated autophagy and NETosis formation in the human and mouse AH lungs, and provide a therapeutic potential of intra-pulmonary delivery of shRNA targeting SNHG16 in this SLE-related lethal manifestation.

Keywords: Alveolar hemorrhage; Autophagy; LncRNA; NETosis; SNHG16; Systemic lupus erythematosus; TLR4; TRAF6.