Trim21 deficiency in mice increases HCC carcinogenesis in a NASH context and is associated with immune checkpoint upregulation.

The global pandemic of metabolic diseases has increased the incidence of hepatocellular carcinoma (HCC) in the context of non-alcoholic steatohepatitis (NASH). The downregulation of the E3 ubiquitin ligase TRIM21 has been linked to poor prognosis in different cancers including HCC. In order to investigate the role of TRIM21 in liver cancer progression on NASH, Trim21+/+ and Trim21-/- male mice were injected with streptozotocin at the neonatal stage. The hypoinsulinemic mice were then fed with a high-fat high-cholesterol diet (HFHCD) for 4, 8 or 12 weeks. All mice developed NASH which systematically resulted in HCC progression. Interestingly, compared to the Trim21+/+ control mice, liver damage was worsened in Trim21-/- mice, with more HCC nodules found after 12 weeks on HFHCD. Immune population analysis in the spleen and liver revealed a higher proportion of CD4+PD-1+ and CD8+PD-1+ T cells in Trim21-/- mice. The liver and HCC tumors of Trim21-/- mice also exhibited an increase in the number of PD-L1+ and CD68+ PD-L1+ cells. Thus, TRIM21 limits the emergence of HCC nodules in mice with NASH by potentially restricting the expression of PD-1 in lymphocytes and PD-L1 in tumors.

Uveitic glaucoma-like features in Yap conditional knockout mice.

Glaucoma is a multifactorial neurodegenerative disease characterized by the progressive and irreversible degeneration of the optic nerve and retinal ganglion cells. Despite medical advances aiming at slowing degeneration, around 40% of treated glaucomatous patients will undergo vision loss. It is thus of utmost importance to have a better understanding of the disease and to investigate more deeply its early causes. The transcriptional coactivator YAP, an important regulator of eye homeostasis, has recently drawn attention in the glaucoma research field. Here we show that Yap conditional knockout mice (Yap cKO), in which the deletion of Yap is induced in both Müller glia (i.e. the only retinal YAP-expressing cells) and the non-pigmented epithelial cells of the ciliary body, exhibit a breakdown of the aqueous-blood barrier, accompanied by a progressive collapse of the ciliary body. A similar phenotype is observed in human samples that we obtained from patients presenting with uveitis. In addition, aged Yap cKO mice harbor glaucoma-like features, including deregulation of key homeostatic Müller-derived proteins, retinal vascular defects, optic nerve degeneration and retinal ganglion cell death. Finally, transcriptomic analysis of Yap cKO retinas pointed to early-deregulated genes involved in extracellular matrix organization potentially underlying the onset and/or progression of the observed phenotype. Together, our findings reveal the essential role of YAP in preserving the integrity of the ciliary body and retinal ganglion cells, thereby preventing the onset of uveitic glaucoma-like features.

RIPK1 in Liver Parenchymal Cells Limits Murine Hepatitis during Acute CCl4-Induced Liver Injury.

Some life-threatening acute hepatitis originates from drug-induced liver injury (DILI). Carbon tetrachloride (CCl4)-induced acute liver injury in mice is the widely used model of choice to study acute DILI, which pathogenesis involves a complex interplay of oxidative stress, necrosis, and apoptosis. Since the receptor interacting protein kinase-1 (RIPK1) is able to direct cell fate towards survival or death, it may potentially affect the pathological process of xenobiotic-induced liver damage. Two different mouse lines, either deficient for Ripk1 specifically in liver parenchymal cells (Ripk1LPC-KO) or for the kinase activity of RIPK1 (Ripk1K45A, kinase dead), plus their respective wild-type littermates (Ripk1fl/fl, Ripk1wt/wt), were exposed to single toxic doses of CCl4. This exposure led in similar injury in Ripk1K45A mice and their littermate controls. However, Ripk1LPC-KO mice developed more severe symptoms with massive hepatocyte apoptosis as compared to their littermate controls. A pretreatment with a TNF-α receptor decoy exacerbated liver apoptosis in both Ripk1fl/fl and Ripk1LPC-KO mice. Besides, a FasL antagonist promoted hepatocyte apoptosis in Ripk1fl/fl mice but reduced it in Ripk1LPC-KO mice. Thus, the scaffolding properties of RIPK1 protect hepatocytes from apoptosis during CCl4 intoxication. TNF-α and FasL emerged as factors promoting hepatocyte survival. These protective effects appeared to be independent of RIPK1, at least in part, for TNF-α, but dependent on RIPK1 for FasL. These new data complete the deciphering of the molecular mechanisms involved in DILI in the context of research on their prevention or cure.

Linking YAP to Müller Glia Quiescence Exit in the Degenerative Retina.

Contrasting with fish or amphibian, retinal regeneration from Müller glia is largely limited in mammals. In our quest toward the identification of molecular cues that may boost their stemness potential, we investigated the involvement of the Hippo pathway effector YAP (Yes-associated protein), which is upregulated in Müller cells following retinal injury. Conditional Yap deletion in mouse Müller cells prevents cell-cycle gene upregulation that normally accompanies reactive gliosis upon photoreceptor cell death. We further show that, in Xenopus, a species endowed with efficient regenerative capacity, YAP is required for their injury-dependent proliferative response. In the mouse retina, where Müller cells do not spontaneously proliferate, YAP overactivation is sufficient to induce their reprogramming into highly proliferative cells. Overall, we unravel a pivotal role for YAP in tuning Müller cell proliferative response to injury and highlight a YAP-EGFR (epidermal growth factor receptor) axis by which Müller cells exit their quiescence state, a critical step toward regeneration.

Retinal Degeneration Triggers the Activation of YAP/TEAD in Reactive Müller Cells.

Purpose: During retinal degeneration, Müller glia cells respond to photoreceptor loss by undergoing reactive gliosis, with both detrimental and beneficial effects. Increasing our knowledge of the complex molecular response of Müller cells to retinal degeneration is thus essential for the development of new therapeutic strategies. The purpose of this work was to identify new factors involved in Müller cell response to photoreceptor cell death. Methods: Whole transcriptome sequencing was performed from wild-type and degenerating rd10 mouse retinas at P30. The changes in mRNA abundance for several differentially expressed genes were assessed by quantitative RT-PCR (RT-qPCR). Protein expression level and retinal cellular localization were determined by western blot and immunohistochemistry, respectively. Results: Pathway-level analysis from whole transcriptomic data revealed the Hippo/YAP pathway as one of the main signaling pathways altered in response to photoreceptor degeneration in rd10 retinas. We found that downstream effectors of this pathway, YAP and TEAD1, are specifically expressed in Müller cells and that their expression, at both the mRNA and protein levels, is increased in rd10 reactive Müller glia after the onset of photoreceptor degeneration. The expression of Ctgf and Cyr61, two target genes of the transcriptional YAP/TEAD complex, is also upregulated following photoreceptor loss. Conclusions: This work reveals for the first time that YAP and TEAD1, key downstream effectors of the Hippo pathway, are specifically expressed in Müller cells. We also uncovered a deregulation of the expression and activity of Hippo/YAP pathway components in reactive Müller cells under pathologic conditions.

Müller glial cell-dependent regeneration of the neural retina: An overview across vertebrate model systems.

Retinal dystrophies are a major cause of blindness for which there are currently no curative treatments. Transplantation of stem cell-derived neuronal progenitors to replace lost cells has been widely investigated as a therapeutic option. Another promising strategy would be to trigger self-repair mechanisms in patients, through the recruitment of endogenous cells with stemness properties. Accumulating evidence in the past 15 year0s has revealed that several retinal cell types possess neurogenic potential, thus opening new avenues for regenerative medicine. Among them, Müller glial cells have been shown to be able to undergo a reprogramming process to re-acquire a stem/progenitor state, allowing them to proliferate and generate new neurons for repair following retinal damages. Although Müller cell-dependent spontaneous regeneration is remarkable in some species such as the fish, it is extremely limited and ineffective in mammals. Understanding the cellular events and molecular mechanisms underlying Müller cell activities in species endowed with regenerative capacities could provide knowledge to unlock the restricted potential of their mammalian counterparts. In this context, the present review provides an overview of Müller cell responses to injury across vertebrate model systems and summarizes recent advances in this rapidly evolving field. Developmental Dynamics 245:727-738, 2016. © 2015 The Authors. Developmental Dynamics published by Wiley Periodicals, Inc.