UBR5 promotes antiviral immunity by disengaging the transcriptional brake on RIG-I like receptors.

The Retinoic acid-Inducible Gene I (RIG-I) like receptors (RLRs) are the major viral RNA sensors essential for the initiation of antiviral immune responses. RLRs are subjected to stringent transcriptional and posttranslational regulations, of which ubiquitination is one of the most important. However, the role of ubiquitination in RLR transcription is unknown. Here, we screen 375 definite ubiquitin ligase knockout cell lines and identify Ubiquitin Protein Ligase E3 Component N-Recognin 5 (UBR5) as a positive regulator of RLR transcription. UBR5 deficiency reduces antiviral immune responses to RNA viruses, while increases viral replication in primary cells and mice. Ubr5 knockout mice are more susceptible to lethal RNA virus infection than wild type littermates. Mechanistically, UBR5 mediates the Lysine 63-linked ubiquitination of Tripartite Motif Protein 28 (TRIM28), an epigenetic repressor of RLRs. This modification prevents intramolecular SUMOylation of TRIM28, thus disengages the TRIM28-imposed brake on RLR transcription. In sum, UBR5 enables rapid upregulation of RLR expression to boost antiviral immune responses by ubiquitinating and de-SUMOylating TRIM28.

Differential roles of RIG-I like receptors in SARS-CoV-2 infection.

Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated protein 5 (MDA5) sense viral RNA and activate antiviral immune responses. Herein we investigate their functions in human epithelial cells, the primary and initial target of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A deficiency in MDA5, RIG-I or mitochondrial antiviral signaling protein (MAVS) enhanced viral replication. The expression of the type I/III interferon (IFN) during infection was impaired in MDA5-/- and MAVS-/-, but not in RIG-I-/-, when compared to wild type (WT) cells. The mRNA level of full-length angiotensin-converting enzyme 2 (ACE2), the cellular entry receptor for SARS-CoV-2, was ~ 2.5-fold higher in RIG-I-/- than WT cells. These data demonstrate MDA5 as the predominant SARS-CoV-2 sensor, IFN-independent induction of ACE2 and anti-SARS-CoV-2 role of RIG-I in epithelial cells.

An Essential Role of UBXN3B in B Lymphopoiesis.

Hematopoiesis is finely regulated to enable timely production of the right numbers and types of mature immune cells to maintain tissue homeostasis. Dysregulated hematopoiesis may compromise antiviral immunity and/or exacerbate immunopathogenesis. Herein, we report an essential role of UBXN3B in maintenance of hematopoietic homeostasis and restriction of immunopathogenesis during respiratory viral infection. Ubxn3b deficient ( Ubxn3b -/- ) mice are highly vulnerable to SARS-CoV-2 and influenza A infection, characterized by more severe lung immunopathology, lower virus-specific IgG, significantly fewer B cells, but more myeloid cells than Ubxn3b +/+ littermates. This aberrant immune compartmentalization is recapitulated in uninfected Ubxn3b -/- mice. Mechanistically, UBXN3B controls precursor B-I (pre-BI) transition to pre-BII and subsequent proliferation in a cell-intrinsic manner, by maintaining BLNK protein stability and pre-BCR signaling. These results reveal an essential role of UBXN3B for the early stage of B cell development.

Differential roles of RIG-I-like receptors in SARS-CoV-2 infection.

The retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated protein 5 (MDA5) are the major viral RNA sensors that are essential for activation of antiviral immune responses. However, their roles in severe acute respiratory syndrome (SARS)-causing coronavirus (CoV) infection are largely unknown. Herein we investigate their functions in human epithelial cells, the primary and initial target of SARS-CoV-2, and the first line of host defense. A deficiency in MDA5 ( MDA5 -/- ), RIG-I or mitochondrial antiviral signaling protein (MAVS) greatly enhanced viral replication. Expression of the type I/III interferons (IFN) was upregulated following infection in wild-type cells, while this upregulation was severely abolished in MDA5 -/- and MAVS -/- , but not in RIG-I -/- cells. Of note, ACE2 expression was ~2.5 fold higher in RIG-I -/- than WT cells. These data demonstrate a dominant role of MDA5 in activating the type I/III IFN response to SARS-CoV-2, and an IFN-independent anti-SARS-CoV-2 role of RIG-I.

CXCL10 Signaling Contributes to the Pathogenesis of Arthritogenic Alphaviruses.

Emerging and re-emerging arthritogenic alphaviruses, such as Chikungunya virus (CHIKV) and O'nyong nyong virus, cause acute and chronic crippling arthralgia associated with inflammatory immune responses. Approximately 50% of CHIKV-infected patients suffer from rheumatic manifestations that last 6 months to years. However, the physiological functions of individual immune signaling pathways in the pathogenesis of alphaviral arthritis remain poorly understood. Here, we report that a deficiency in CXCL10, which is a chemoattractant for monocytes/macrophages/T cells, led to the same viremia as wild-type animals, but fewer immune infiltrates and lower viral loads in footpads at the peak of arthritic disease (6-8 days post infection). Macrophages constituted the largest immune cell population in footpads following infection, and were significantly reduced in Cxcl10-/- mice. The viral RNA loads in neutrophils and macrophages were reduced in Cxcl10-/- compared to wild-type mice. In summary, our results demonstrate that CXCL10 signaling promotes the pathogenesis of alphaviral disease and suggest that CXCL10 may be a therapeutic target for mitigating alphaviral arthritis.

The aging bladder phenotype is not the direct consequence of bladder aging.

AIMS: The prevalence of urinary dysfunction increases with age, yet therapies are often suboptimal. Incomplete understanding of the linkages between system, organ, and tissue domains across lifespan remains a knowledge gap. If tissue-level changes drive the aging bladder phenotype, parallel changes should be observed across these domains. In contrast, a lack of inter-domain correlation across age groups would support the hypothesis that urinary performance is a measure of the physiologic reserve, dependent on centrally-mediated adaptive mechanisms in the aging system. METHODS: Male and female mice across four age groups underwent sequential voiding spot assays, pressure/flow cystometry, bladder strip tension studies, histology, and quantitative PCR analyses. The primary objective of this study was to test the impact of age on the cortical, autonomic, tissue functional and structural, and molecular domains, and identify inter-domain correlations among variables showing significant changes with age within these domains. RESULTS: Behavior revealed diminished peripheral voiding and spot size in aged females. Cystometry demonstrated increased postvoid residual and loss of volume sensitivity, but the preservation of voiding contraction power, with almost half of oldest-old mice failing under cystometric stress. Strip studies revealed no significant differences in adrenergic, cholinergic, or EFS sensitivity. Histology showed increased detrusor and lamina propria thickness, without a change in collagen/muscle ratio. Adrb2 gene expression decreased with age. No consistent inter-domain correlations were found across age groups. CONCLUSIONS: Our findings are consistent with a model in which centrally-mediated adaptive failures to aging stressors are more influential over the aging bladder phenotype than local tissue changes.