Xiaotao Duan

Shiga toxins (Stx), produced by Shiga toxin-producing Escherichia coli, preferentially attack renal tissue and frequently induce acute kidney injury (AKI) and renal failure. To prevent irreversible damage, the injured renal tissue, particularly renal tubular epithelium, mounts a remodeling and regeneration response to repair itself. However, how such intrinsic renal repair processes are initiated and coordinated in infected renal tubular regions remains elusive. Herein, we reported that macula densa apparatus, in addition to its conventional role as a salt sensor in nephron, can function as an endogenous sensor for exogenous toxins (e.g., Stx). We demonstrated that macula densa cells orchestrate a rapid repair niche by initiating transcriptional activation of repair and regeneration factors in both Stx-injured murine models and human kidney organoids. Mechanistically, we showed that in response to Stx exposure, macula densa cells release a specific repair factor CCN1, which effectively promotes the regeneration of toxin-injured renal tubular epithelium and facilitates renal tubular repair through integrin-mediated signaling pathways. Moreover, we demonstrated that treatment with recombinant CCN1 can greatly ameliorate the structural damage and significantly restore the proximal tubular reabsorption capacity in Stx-infected kidney organoids. Our finding highlights a novel role of macula densa apparatus in toxin-induced renal injury, and paves a new avenue for treatment of AKI-associated renal diseases.

Reactive thiols of proteinaceous cysteines are vital to cell biology by serving as sensor, effector and buffer of environmental redox fluctuations. Being the major source, as well as the prime target, of reactive oxygen species (ROS), mitochondria confront great challenges in preserving their thiol pool. Here we show that ROS modulator 1 (ROMO1), a small inner mitochondrial membrane protein, plays a role in protecting the mitochondrial cysteinome. ROMO1 is redox sensitive and reactive and overexpression can prevent deleterious oxidation of proteinaceous thiols. ROMO1 upregulation leads to a reductive shift of the mitochondrial cysteinome, exerting beneficial effects on mitochondria, such as promoting energy metabolism and Ca²⁺ uniport while inhibiting vicious membrane permeability transition. Importantly, ROMO1 overexpression reverses mitochondrial cysteinome oxidations in multiple organs and slows functional decline in aged male mice. These findings unravel a redox regulatory mechanism of the mitochondrial cysteinome and mark ROMO1 as a potential target for combating oxidative stress and improving healthspan.

Objective To explore the effect of the knockdown of transmembrane 9 superfamily protein member 2 (TM9SF2) on the replication of vesicular stomatitis virus (VSV), and investigate its role in the mechanism of antiviral innate immunity. Methods Small interfering RNA (siRNA) was used to knock down the TM9SF2 gene in human non-small cell lung cancer A549 cells. The CCK-8 method was used to assess cell proliferation. A VSV-green fluorescent protein (VSV-GFP) infected cell model was established. The plaque assay was used to measure the viral titer in the supernatant. RT-qPCR and Western blotting were employed to quantify the mRNA and protein levels of VSV genome replication in A549 cells following VSV infection, as well as the expression of interferon β (IFN-β) mRNA and interferon regulatory factor 3 (IRF3) protein phosphorylation following polyinosinic-polycytidylic acid (poly(I:C)) stimulation. Results Compared to the negative control, the knockdown of TM9SF2 exhibited a significant effect, with no observed impact on A549 cell proliferation. The VSV-GFP infected A549 cell model was successfully established. After viral stimulation, fluorescence intensity was reduced following TM9SF2 knockdown, and the mRNA and protein levels of VSV were significantly downregulated. The viral titer of VSV was decreased. After poly(I:C) stimulation, TM9SF2 knockdown significantly upregulated the mRNA level of IFN-β and the phosphorylation level of IRF3 protein. Conclusion The knockdown of TM9SF2 inhibits the replication of vesicular stomatitis virus, and positively regulates the type I interferon signaling pathway, thus enhancing the host's antiviral innate immune response.

TM9SF2 belongs to a family of highly conserved nonaspanin proteins, and has been frequently identified as one of the important host factors for a plethora of lethal pathogens and toxins in previous genome-wide screening studies. We reported herein a novel molecular mechanism of TM9SF2 in mediating the cytotoxicity of ricin, a type II ribosome-inactivating protein. We first showed that TM9SF2 displays a non-redundant requirement for ricin-induced cytotoxicity within the nonaspanin family. Then we found that genetic interference of TM9SF2 substantially affects/remodels intracellular cholesterol trafficking, which results in abnormal cholesterol accumulation in Golgi compartments and causes severe Golgi fragmentation. The disruption of Golgi integrity and network impedes the retrograde transport of ricin and thus attenuates ricin-induced cytotoxicity. We further verified this mechanism by pharmacological manipulation of cholesterol metabolism (e.g., by using A939572 and avasimibe, etc.), which well restores the integrity of the Golgi apparatus and reverses the ricin-resistant phenotype induced by TM9SF2 knockdown. Our finding provides new mechanistic insights into the pathology and toxicology of ricin and could potentially be applied to other ribosome-inactivating toxins.

While linear ubiquitin plays critical roles in multiple cell signaling pathways, few substrates have been identified. Global profiling of linear ubiquitin substrates represents a significant challenge because of the low endogenous level of linear ubiquitination and the background interference arising from highly abundant ubiquitin linkages (e.g. K48- and K63-) and from the non-specific attachment of interfering proteins to the linear polyubiquitin chain. We developed a bio-orthogonal linear ubiquitin probe by site-specific encoding of a norbornene amino acid on ubiquitin (NAEK-Ub). This probe facilitates covalent labeling of linear ubiquitin substrates in live cells and enables selective enrichment and identification of linear ubiquitin-modified proteins. Given the fact that the frequent overexpression of the linear linkage-specific deubiquitinase OTULIN correlates with poor prognosis in glioblastoma, we demonstrated the feasibility of the NAEK-Ub strategy by identifying and validating substrates of linear ubiquitination in patient-derived glioblastoma stem-like cells (GSCs). We identified STAT3 as a bona fide substrate of linear ubiquitin, and showed that linear ubiquitination negatively regulates STAT3 activity by recruitment of the phosphatase TC-PTP to STAT3. Furthermore, we demonstrated that preferential expression of OTULIN in GSCs restricts linear ubiquitination on STAT3 and drives persistent STAT3 signaling, and thereby maintains the stemness and self-renewal of GSCs.

Sonic hedgehog (Shh) signaling plays a critical role in regulating cerebellum development by maintaining the physiological proliferation of granule neuron precursors (GNPs), and its dysregulation leads to the oncogenesis of medulloblastoma. O-GlcNAcylation (O-GlcNAc) of proteins is an emerging regulator of brain function that maintains normal development and neuronal circuitry. Here, we demonstrate that O-GlcNAc transferase (OGT) in GNPs mediate the cerebellum development, and the progression of the Shh subgroup of medulloblastoma. Specifically, OGT regulates the neurogenesis of GNPs by activating the Shh signaling pathway via O-GlcNAcylation at S355 of GLI family zinc finger 2 (Gli2), which in turn promotes its deacetylation and transcriptional activity via dissociation from p300, a histone acetyltransferases. Inhibition of OGT via genetic ablation or chemical inhibition improves survival in a medulloblastoma mouse model. These data uncover a critical role for O-GlcNAc signaling in cerebellar development, and pinpoint a potential therapeutic target for Shh-associated medulloblastoma.

Mutations of the X-linked methyl-CpG-binding protein 2 (MECP2) gene in humans are responsible for most cases of Rett syndrome (RTT), an X-linked progressive neurological disorder. While genome-wide screens in clinical trials have revealed several putative RTT-associated mutations in MECP2, their causal relevance regarding the functional regulation of MeCP2 at the etiologic sites at the protein level requires more evidence. In this study, we demonstrated that MeCP2 was dynamically modified by O-linked-β-N-acetylglucosamine (O-GlcNAc) at threonine 203 (T203), an etiologic site in RTT patients. Disruption of the O-GlcNAcylation of MeCP2 specifically at T203 impaired dendrite development and spine maturation in cultured hippocampal neurons, and disrupted neuronal migration, dendritic spine morphogenesis, and caused dysfunction of synaptic transmission in the developing and juvenile mouse cerebral cortex. Mechanistically, genetic disruption of O-GlcNAcylation at T203 on MeCP2 decreased the neuronal activity-induced induction of Bdnf transcription. Our study highlights the critical role of MeCP2 T203 O-GlcNAcylation in neural development and synaptic transmission potentially via brain-derived neurotrophic factor.