Hepatocyte TIPE2 is a fasting-induced Raf-1 inactivator that drives hepatic gluconeogenesis to maintain glucose homeostasis

TIPE2 protein restrains invariant NKT activation and protects against immune-mediated hepatitis in mice

BACKGROUND AND AIMS

Concanavalin A (ConA) administration induces rapid and severe liver injury in mice, and invariant natural killer T (iNKT) cells are recognized to be the key effector cells in this process. However, the underlying regulatory mechanisms are not well defined.

APPROACH AND RESULTS

We found that iNKT cells constitutively expressed TIPE2 (tumor necrosis factor-α-induced protein 8-like 2, or TNFAIPL2). Genetic TIPE2 ablation strongly sensitized mice to ConA-induced hepatitis, accompanied by hyperactivation of iNKT cells. Moreover, Tipe2-/- mice were also more susceptible to α-galactosylceramide-induced liver injury, with elevated serum ALT levels and enhanced proinflammatory cytokine production. CD1d signaling blockade or iNKT cell elimination through antibodies reduced the effect of TIPE2 deficiency on liver injury. Mechanistic studies revealed that TIPE2 in iNKT cells functioned as a negative regulator, limiting iNKT cell activity and cytokine production through PIP3- AKT/mTOR pathway. TIPE2-mediated protection from liver injury was further validated by the administration of adeno-associated viruses expressing TIPE2, which effectively ameliorated ConA-induced hepatic injury. However, TIPE2 was dispensable in 2 other liver injury models, including D-GalN/LPS and acetaminophen-induced hepatitis.

CONCLUSIONS

Our findings reveal a new role of TIPE2 in the attenuation of iNKT cell-mediated hepatic injury. We propose that TIPE2 serves as an important regulator of immune homeostasis in the liver and might be exploited for the therapeutic treatment of autoimmune liver diseases.

TIPE2 deficiency amplifies inflammation and immune dysregulation in MASH through modulating hepatic lipid metabolism and immune cell function

BACKGROUND

Metabolic Dysfunction-Associated Steatohepatitis (MASH) affects nearly 25% of the global population, yet there are no effective pharmacological treatments. Tumor necrosis factor α-induced protein 8-like 2 (TIPE2) is expressed in various immune cells and is crucial for regulating both innate and adaptive immune responses. However, its role in MASH development and the underlying mechanisms remain unclear.

METHOD

In this study, the role of TIPE2 in MASH was investigated using TIPE2 knockout (KO) mice and human hepatic LO2 cells. Immune cell infiltration, cytokine levels, and gene expression were analyzed. Techniques included flow cytometry for immune cell profiling, cytokine analysis, RNA sequencing, and quantitative PCR (qPCR) for validating gene expression changes.

RESULTS

TIPE2 was identified as a key regulator in MASH, influencing immune modulation and metabolic processes. TIPE2 KO mice exhibited increased infiltration and activation of natural killer (NK) cells, M1 macrophages, and myeloid-derived suppressor cells (MDSCs), along with elevated pro-inflammatory cytokines such as IFN-gamma, TNF-alpha, IL- 1 beta, and IL- 6. MDSCs from TIPE2 KO mice demonstrated enhanced PD-L1 expression, contributing to chronic liver inflammation through T cell suppression. RNA sequencing revealed that TIPE2 overexpression in human hepatic LO2 cells upregulated genes associated with amino acid biosynthesis, carbon metabolism, lipid regulation, glycolysis, and gluconeogenesis. These findings were supported by qPCR analyses of liver samples from mice, confirming TIPE2's role in maintaining lipid homeostasis and modulating immune responses.

CONCLUSION

The study highlights the pivotal role of TIPE2 in immune regulation and its influence on immune cell activation and inflammatory responses, which are critical in MASH progression. By exploring TIPE2-mediated immune regulation and its impact on the interplay between immune cell dynamics and liver metabolism, this research underscores TIPE2's central role in linking immune dysfunction to metabolic disturbances in MASH.

TNFAIP8L2 maintains hair cell function and regulates age-related hearing loss via mTORC1 signaling

Age-related hearing loss (ARHL) is one of the most prevalent and complex disorders. Our previous study demonstrated that abnormal activation of mammalian target of rapamycin complex 1 (mTORC1) signaling in the cochlear neurosensory epithelium causes auditory hair cell (HC) damage and contributes to ARHL. However, the underlying mechanism of mTORC1 activation remains unclear. In this study, we identified tumor necrosis factor-alpha-induced protein 8-like 2 (TNFAIP8L2), an immune regulatory gene, as a potential candidate. To elucidate the effect of TNFAIP8L2 on mTORC1 signaling in the neurosensory epithelium and on hearing function, we generated a Tnfaip8l2-deficient (Tnfaip8l2-/-) mouse model. We discovered that Tnfaip8l2 deficiency led to features of oxidative stress in cochlear HCs and age-related hearing degeneration, exhibiting a similar phenotype to the mTORC1-over-activated Tsc1-cKO mice described previously. Furthermore, rapamycin, a well-known mTORC1 inhibitor, significantly mitigated the hearing dysfunction caused by Tnfaip8l2-deficiency. Mechanistically, we found that TNFAIP8L2 regulates mTORC1 signaling by simultaneously inhibiting the GTPase activity of Ras homolog enriched in brain (RHEB) and Ras-related C3 botulinum toxin substrate 1 (RAC1). Notably, both RHEB and RAC1 inhibitors alleviated the hearing phenotype observed in Tnfaip8l2-/- mice by inhibiting mTORC1 signaling. Collectively, our results provide insights into the activation of the mTORC1 pathway in aged mouse cochleae and positions TNFAIP8L2 as a valuable theoretical strategy.