To study the mechanistic role of myeloid-specific Notch1 knockout inhibiting STING signaling to regulate hepatocyte lipophagy.

A mouse model of nonalcoholic steatohepatitis (NASH) was established using a high-fat diet (HFD) and mouse bone marrow-derived macrophages (BMMs). Primary hepatocytes were isolated to construct a co-culture system. Twelve Notch1^FL/FL mice were randomly divided into two groups: the Notch1^FL/FL + normal diet (NCD) and the Notch1^FL/FL + HFD group. Further, 12 Notch1^M-KO mice were randomly divided into two groups: Notch1^M-KO + NCD, and Notch1^M-KO + HFD group.Serum alanine aminotransferase (sALT), total cholesterol (TC) and triglyceride (TG) were collected from mice serum samples. Liver tissue samples were collected for H&E staining, immunofluorescence (IF), Western blot and qRT-PCR. Tumor necrosis factor (TNF)-α was detected in the supernatant by enzyme-linked immunosorbent assay (ELISA). The comparison of inter group data was conducted using a t-test.

The mouse NASH model, mouse BMMs co-culture system, and primary hepatocytes were successfully constructed. Compared with the Notch1^FL/FL + HFD group, the Notch1^M-KO + HFD group showed a significant increase in serum ALT [(250.02 ± 58.21) U/L vs (370.70 ± 54.57) U/L, t = 3.705, P = 0.004], TG [(29.90 ± 3.54) mg/g vs (43.83 ± 8.56) mg/g, t = 3.685, P = 0.004], and TC [(33.70 ± 8.43) mg/g vs (90.53 ± 12.53) mg/g, t = 9.917, P < 0.001]. HE staining of liver tissue showed remarkable balloon-like alterations in liver cells, while IF staining demonstrated increased macrophage infiltration (t = 7.346, P < 0.001). Compared with the hepatocyte group co-cultured with Notch1^FL/FL BMMs, the BODIPY probe showed a significant increase in lipid droplet (LDs) deposition in liver cells in the Notch1^M-KO group (t = 3.835, P < 0.001). The co-localization of lysosomal associated membrane protein 1 (LAMP1), LDs (t = 7.103, P < 0.001), microtubule-associated protein light chain 3 (LC3) -II/LC3-I (t = 5.0, P = 0.007), and autophagy associated gene 12 (Atg12) (t = 28.36, P < 0.001) had decreased expression, while P-62 had increased expression (t = 3.253, P = 0.03), indicating a decrease in autophagic flow. Additionally, LC3 and LDs colocalization decreased (t = 5.24, P = 0.0003), indicating reduced lipophagy. Compared with the Notch1^FL/FL group, the Notch1^M-KO BMMS mouse group showed an increase in the expression of p-STING (t = 5.318, P = 0.006), p-TANK1 binding kinase 1 (TKB1) (t = 6.467, P = 0.002), p-interferon regulatory factor 3 (IRF3) (t = 14.61, P < 0.001), and p-P65 (t = 12.7, P = 0.002) protein, accompanied by mRNA expression of the inflammatory mediators interferon (IFN)-β (t = 7.978, P < 0.001), TNFα (t = 8.496, P = 0.001), interleukin-1 β (IL-1 β) (t = 4.7, P < 0.001), and CXCL-10 (t = 4.428, P = 0.001). The STING gene was knocked out in the BMMs Notch1^M-KO mice using CRISPR/Cas9. Compared with the CRISPR-Control group, the expression of P-TKB1 (t = 2.909, P = 0.044), p-IRF3 (t = 10.96, P < 0.001), p-IRF3 (t = 10.96, P < 0.001), and p-P65 (t = 7.091, P = 0.002) proteins was lower in the STING-KO BMMs group. The release of TNF-α in the supernatant was decreased (732.3 ± 129.35 pg/ml vs. 398.17 ± 47.15 pg/ml, t = 4.204, P = 0.014). However, in hepatocytes co-cultured with STING-KO BMMs, LC3-II/LC3-I (t = 7.546, P = 0.001) increased, p-62 (t = 10.96, P < 0.001) expression decreased, autophagic flow increased, and the colocalization of LC3 and LDs increased, lipophagy increased, and LDs deposition decreased.

Myeloid-specific Notch1 knockout can activate macrophages STING signaling, increase the expression of inflammatory mediator genes, inhibit the occurrence of autophagy flow and lipophagy in hepatocyte cells, and aggravate LDs deposition and NASH progression.

Fatty liver; Notch1; Stimulafor of interferon genes; Autophagy; Lipophagy; Signal pathway