Inhibition of MALT1 Decreases Neuroinflammation and Pathogenicity of Virulent Rabies Virus in Mice

PRRSV utilizes MALT1-regulated autophagy flux to switch virus spread and reserve

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen, which can survive host antiviral immunity with various mechanisms. PRRSV infection induces macroautophagy/autophagy, facilitating virus replication. MALT1, a central immune regulator, was manipulated by PRRSV to optimize viral infection at different stages of the virus cycle. In this study, the key role of MALT1 in autophagy regulation during PRRSV infection was characterized, enlightening the role of autophagy flux in favor of virus spread and persistent infection. PRRSV-induced autophagy was confirmed to facilitate virus proliferation. Furthermore, autophagic fusion was dynamically regulated during PRRSV infection. Importantly, PRRSV-induced MALT1 facilitated autophagosome-lysosome fusion and autolysosome formation, thus contributing to autophagy flux and virus proliferation. Mechanically, MALT1 regulated autophagy via mediating MTOR-ULK1 and -TFEB signaling and affecting lysosomal homeostasis. MALT1 inhibition by inhibitor Mi-2 or RNAi induced lysosomal membrane permeabilization (LMP), leading to the block of autophagic fusion. Further, MALT1 overexpression alleviated PRRSV-induced LMP via inhibiting ROS generation. In addition, blocking autophagy flux suppressed virus release significantly, indicating that MALT1-maintained complete autophagy flux during PRRSV infection favors successful virus spread and its proliferation. In contrast, autophagosome accumulation upon MALT1 inhibition promoted PRRSV reserve for future virus proliferation once the autophagy flux recovers. Taken together, for the first time, these findings elucidate that MALT1 was utilized by PRRSV to regulate host autophagy flux, to determine the fate of virus for either proliferation or reserve.Abbreviations: 3-MA: 3-methyladenine; BafA1: bafilomycin A1; BFP/mBFP: monomeric blue fluorescent protein; CQ: chloroquine; DMSO: dimethyl sulfoxide; dsRNA: double-stranded RNA; GFP: green fluorescent protein; hpi: hours post infection; IFA: indirect immunofluorescence assay; LAMP1: lysosomal associated membrane protein 1; LGALS3: galectin 3; LLOMe: L-leucyl-L-leucine-methyl ester; LMP: lysosomal membrane permeabilization; mAb: monoclonal antibody; MALT1: MALT1 paracaspase; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; NFKB/NF-κB: nuclear factor kappa B; nsp: nonstructural protein; ORF: open reading frame; pAb: polyclonal antibody; PRRSV: porcine reproductive and respiratory syndrome virus; PRRSV-N: PRRSV nucleocapsid protein; Rapa: rapamycin; RFP: red fluorescent protein; ROS: reactive oxygen species; SBI: SBI-0206965; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; TCID50: 50% tissue culture infective dose; TFEB: transcription factor EB; ULK1: unc-51 like autophagy activating kinase 1.

Prevalence and Factor Associated with Anti-N-Methyl-D-Aspartate Receptor Encephalitis Among Patients with Medical Conditions: A Systematic Review and Meta-Analysis

BACKGROUND

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a severe autoimmune encephalitis due to immune production of anti-NMDAR antibodies against the NR1 subunit of the NMDA receptor which is present throughout the central nervous system. This condition had been reported to be prevalent in patients with certain medical conditions; however so far, there have been limited systematic reviews and meta-analyses on the prevalence and factors associated.

OBJECTIVE

This study was to determine the prevalence and factors associated with anti-NMDAR encephalitis among affected patients.

MATERIAL AND METHODS

The protocol of this study has been registered (2019: CRD42019142002) with the International Prospective Register of Systematic Reviews (PROSPERO). The primary outcome was the incidence or prevalence of anti-NMDAR encephalitis and secondary outcomes were factors associated with anti-NMDAR encephalitis.

RESULTS

There were 11 studies and a total of 873 million patients taken from high-risk populations across 11 countries that were included in the primary analysis. The overall pooled prevalence of anti-NMDAR encephalitis among patients with medical conditions was 7.0% (95% CI = 4.4, 9.6). Those with first episode of psychosis or schizophrenia were at a higher risk of developing anti-NMDAR encephalitis with an odds ratio of 5.976 (95% CI = 1.122, 31.825).

CONCLUSION

We found that almost one-tenth of patients with medical conditions had anti-NMDAR encephalitis; particularly those with first episode of psychosis or schizophrenia were among the high-risk medical conditions.

Targeting of MALT1 May Improve Functional Recovery and Attenuate Microglia M1 Polarization-Mediated Neuroinflammation During Spinal Cord Injury

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is involved in neural injury, neuroinflammation, microglia activation, and polarization, while its function in spinal cord injury (SCI) remains unclear. Thus, this study aimed to evaluate the role of MALT1 modification on SCI recovery and its underlying mechanism. SCI surgery or sham surgery was performed in Sprague-Dawley rats. Then, MALT1 knockdown or negative control lentivirus was injected into SCI rats. Subsequently, MALT1 expression, locomotor capability, neural injury, markers for microglia activation and polarization, inflammatory cytokine expressions, and nuclear factor (NF)-κB pathway were detected. SCI rats exhibited higher MALT1 expression, microglia activation and M1 polarization, neuroinflammation, and NF-κB pathway activation, while worse locomotor capacity compared to sham rats (all P < 0.05). In SCI rats, MALT1 knockdown alleviated Basso, Beattie, and Bresnahan score from 10 to 28 days and attenuated HE staining reflected neural injury (all P < 0.05). Besides, MALT1 knockdown declined the number of IBA1⁺ cells, IBA1⁺ iNOS⁺ cells, and IBA1⁺ CD86⁺ cells, while enhanced the number of IBA1⁺ Arg1⁺ cells and IBA1⁺ CD206⁺ cells in SCI rats (all P < 0.05). Meanwhile, MALT1 knockdown declined the expressions of IL-1β, IL-6, and TNF-α in SCI (all P < 0.05), but did not affect IL-10 expression (P > 0.05). Furthermore, MALT1 knockdown suppressed NF-κB pathway activation validated by immunofluorescence staining and western blot assays (all P < 0.05). MALT1 knockdown improves functional recovery, attenuates microglia activation, M1 polarization, and neuroinflammation via inhibiting NF-κB pathway in SCI.

Porcine Reproductive and Respiratory Syndrome Virus Adapts Antiviral Innate Immunity via Manipulating MALT1

To fulfill virus replication and persistent infection in hosts, viruses have to find ways to compromise innate immunity, including timely impedance on antiviral RNases and inflammatory responses. Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen causing immune suppression. MALT1 is a central immune regulator in both innate and adaptive immunity. In this study, MALT1 was confirmed to be induced rapidly upon PRRSV infection and mediate the degradation of two anti-PRRSV RNases, MCPIP1 and N4BP1, relying on its proteolytic activity, consequently facilitating PRRSV replication. Multiple PRRSV nsps, including nsp11, nsp7β, and nsp4, contributed to MALT1 elicitation. Interestingly, the elevated expression of MALT1 began to decrease once intracellular viral expression reached a high enough level. Higher infection dose brought earlier MALT1 inflection. Further, PRRSV nsp6 mediated significant MALT1 degradation via ubiquitination-proteasome pathway. Downregulation of MALT1 suppressed NF-κB signals, leading to the decrease in proinflammatory cytokine expression. In conclusion, MALT1 expression was manipulated by PRRSV in an elaborate manner to antagonize precisely the antiviral effects of host RNases without excessive and continuous activation of inflammatory responses. These findings throw light on the machinery of PRRSV to build homeostasis in infected immune system for viral settlement.

Aberrant blood MALT1 and its relevance with multiple organic dysfunctions, T helper cells, inflammation, and mortality risk of sepsis patients

Background

MALT1 is linked with multiple organic dysfunctions, inflammatory storm, and T helper (Th) cell differentiation. Herein, the current study aimed to investigate the correlation of peripheral blood mononuclear cell (PBMC) MALT1 with Th1 cells, Th17 cells, and prognosis of sepsis patients.

Methods

In general, 78 sepsis patients and 40 health controls (HCs) were enrolled. MALT1 expression was detected in PBMCs from all subjects by RT‐qPCR. Besides, Th1 and Th17 cells were measured in PBMCs from sepsis patients by flow cytometry; interleukin 17A (IL‐17A) and interferon gamma (IFN‐γ) were determined in serum from sepsis patients by ELISA.

Results

MALT1 expression was higher in sepsis patients than HCs (p < 0.001). MALT1 expression was positively correlated with Th17 cells (r_s = 0.291, p = 0.038) and IL‐17A (r_s = 0.383, p = 0.001), but not with Th1 cells (r_s = 0.204, p = 0.151) or IFN‐γ (r_s = 0.175, p = 0.125) in sepsis patients. MALT1 expression was positively correlated with APACHE II score (r_s = 0.275, p = 0.015), C‐reactive protein (CRP) (r_s = 0.257, p = 0.023), and sequential organ failure assessment (SOFA) score (r_s = 0.306, p = 0.006) (MALT1 expression was positively correlated with SOFA respiratory system score (r_s = 0.348, p = 0.002), and SOFA liver score (r_s = 0.260, p = 0.021), but not with SOFA scores in nervous system, cardio vascular system, coagulation, and renal system (all p > 0.05)). MALT1 expression (p = 0.010), Th1 cells (p = 0.010), Th17 cells (p = 0.038), and IL‐17A (p = 0.012), except for IFN‐γ (p = 0.102), elevated in sepsis deaths compared with sepsis survivors.

Conclusion

PBMC MALT1 is highly expressed in sepsis patients with its overexpression associated with multiple organic dysfunctions, elevated Th17 cells, and increased mortality risk.

Post-translational modification of MALT1 and its role in B cell- and T cell-related diseases

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a multifunctional protein. MALT1 functions as an adaptor protein to assemble and recruit proteins such as B-cell lymphoma 10 (BCL10) and caspase-recruitment domain (CARD)-containing coiled-coil protein 11 (CARD11). Conversely it also acts as a paracaspase to cleave specified substrates. Because of its involvement in immunity, inflammation and cancer through its dual functions of scaffolding and catalytic activity, MALT1 is becoming a promising therapeutic target in B cell- and T cell-related diseases. There is growing evidence that the function of MALT1 is subtly modulated via post-translational modifications. This review summarized recent progress in relevant studies regarding the physiological and pathophysiological functions of MALT1, post-translational modifications of MALT1 and its role in B cell- and T cell- related diseases. In addition, the current available MALT1 inhibitors were also discussed.

Dual Role of Toll-Like Receptor 7 in the Pathogenesis of Rabies Virus in a Mouse Model

Rabies, caused by rabies virus (RABV), is a fatal encephalitis in humans and other mammals, which continues to present a public health threat in most parts of the world. Our previous study demonstrated that Toll-like receptor 7 (TLR7) is essential in the induction of anti-RABV antibodies via the facilitation of germinal center formation. In the present study, we investigated the role of TLR7 in the pathogenicity of RABV in a mouse model. Using isolated plasmacytoid dendritic cells (pDCs), we demonstrated that TLR7 is an innate recognition receptor for RABV. When RABV invaded from the periphery, TLR7 detected viral single-stranded RNA and triggered immune responses that limited the virus's entry into the central nervous system (CNS). When RABV had invaded the CNS, its detection by TLR7 led to the production of cytokines and chemokines and an increase the permeability of the blood-brain barrier. Consequently, peripheral immune cells, including pDCs, macrophages, neutrophils, and B cells infiltrated the CNS. While this immune response, triggered by TLR7, helped to clear viruses, it also increased neuroinflammation and caused immunopathology in the mouse brain. Our results demonstrate that TLR7 is an innate recognition receptor for RABV, which restricts RABV invasion into the CNS in the early stage of viral infection but also contributes to immunopathology by inducing neuroinflammation.IMPORTANCE Developing targeted treatment for RABV requires understanding the innate immune response to the virus because early virus clearance is essential for preventing the fatality when the infection has progressed to the CNS. Previous studies have revealed that TLR7 is involved in the immune response to RABV. Here, we establish that TLR7 recognizes RABV and facilitates the production of some interferon-stimulated genes. We also demonstrated that when RABV invades into the CNS, TLR7 enhances the production of inflammatory cytokines which contribute to immunopathology in the mouse brain. Taken together, our findings suggest that treatments for RABV must consider the balance between the beneficial and harmful effects of TLR7-triggered immune responses.

Monophosphoryl-Lipid A (MPLA) is an Efficacious Adjuvant for Inactivated Rabies Vaccines

Rabies, as one of the most threatening zoonoses in the world, causes a fatal central nervous system (CNS) disease. So far, vaccination with rabies vaccines has been the most effective measure to prevent and control this disease. At present, inactivated rabies vaccines are widely used in humans and domestic animals. However, humoral immune responses induced by inactivated rabies vaccines are relatively low and multiple shots are required to achieve protective immunity. Supplementation with an adjuvant is a practical way to improve the immunogenicity of inactivated rabies vaccines. In this study, we found that monophosphoryl-lipid A (MPLA), a well-known TLR4 agonist, could significantly promote the maturation of bone marrow-derived dendritic cells (BMDC) through a TLR4-dependent pathway in vitro and the maturation of conventional DCs (cDCs) in vivo. We also found that MPLA, serving as an adjuvant for inactivated rabies vaccines, could significantly facilitate the generation of T follicular helper (Tfh) cells, germinal center (GC) B cells, and plasma cells (PCs), consequently enhancing the production of RABV-specific total-IgG, IgG2a, IgG2b, and the virus-neutralizing antibodies (VNAs). Furthermore, MPLA could increase the survival ratio of mice challenged with virulent RABV. In conclusion, our results demonstrate that MPLA serving as an adjuvant enhances the intensity of humoral immune responses by activating the cDC-Tfh-GC B axis. Our findings will contribute to the improvement of the efficiency of traditional rabies vaccines.

MALT1 Proteolytic Activity Suppresses Autoimmunity in a T Cell Intrinsic Manner

MALT1 is a central signaling component in innate and adaptive immunity by regulating NF-κB and other key signaling pathways in different cell types. Activities of MALT1 are mediated by its scaffold and protease functions. Because of its role in lymphocyte activation and proliferation, inhibition of MALT1 proteolytic activity is of high interest for therapeutic targeting in autoimmunity and certain lymphomas. However, recent studies showing that Malt1 protease-dead knock-in (Malt1-PD) mice suffer from autoimmune disease have somewhat tempered the initial enthusiasm. Although it has been proposed that an imbalance between immune suppressive regulatory T cells (Tregs) and activated effector CD4+ T cells plays a key role in the autoimmune phenotype of Malt1-PD mice, the specific contribution of MALT1 proteolytic activity in T cells remains unclear. Using T cell-conditional Malt1 protease-dead knock-in (Malt1-PDT) mice, we here demonstrate that MALT1 has a T cell-intrinsic role in regulating the homeostasis and function of thymic and peripheral T cells. T cell-specific ablation of MALT1 proteolytic activity phenocopies mice in which MALT1 proteolytic activity has been genetically inactivated in all cell types. The Malt1-PDT mice have a reduced number of Tregs in the thymus and periphery, although the effect in the periphery is less pronounced compared to full-body Malt1-PD mice, indicating that also other cell types may promote Treg induction in a MALT1 protease-dependent manner. Despite the difference in peripheral Treg number, both T cell-specific and full-body Malt1-PD mice develop ataxia and multi-organ inflammation to a similar extent. Furthermore, reconstitution of the full-body Malt1-PD mice with T cell-specific expression of wild-type human MALT1 eliminated all signs of autoimmunity. Together, these findings establish an important T cell-intrinsic role of MALT1 proteolytic activity in the suppression of autoimmune responses.

Mepazine Inhibits RANK-Induced Osteoclastogenesis Independent of Its MALT1 Inhibitory Function

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is an intracellular cysteine protease (paracaspase) that plays an integral role in innate and adaptive immunity. The phenothiazine mepazine has been shown to inhibit the proteolytic activity of MALT1 and is frequently used to study its biological role. MALT1 has recently been suggested as a therapeutic target in rheumatoid arthritis. Here, we analyzed the effect of mepazine on the receptor activator of nuclear factor κ-B (RANK)-induced osteoclastogenesis. The treatment of mouse bone marrow precursor cells with mepazine strongly inhibited the RANK ligand (RANKL)-induced formation of osteoclasts, as well as the expression of several osteoclast markers, such as TRAP, cathepsin K, and calcitonin. However, RANKL induced osteoclastogenesis equally well in bone marrow cells derived from wild-type and Malt1 knock-out mice. Furthermore, the protective effect of mepazine was not affected by MALT1 deficiency. Additionally, the absence of MALT1 did not affect RANK-induced nuclear factor κB (NF-κB) and activator protein 1 (AP-1) activation. Overall, these studies demonstrate that MALT1 is not essential for RANK-induced osteoclastogenesis, and implicate a MALT1-independent mechanism of action of mepazine that should be taken into account in future studies using this compound.