Background & Aims

Retinoic acid inducible gene I (RIG-I)-like receptors (RLRs), including RIG-I, melanoma differentiation-associated protein 5 (MDA5), and laboratory of genetics and physiology 2 (LGP2), sense viral RNA to induce the antiviral interferon (IFN) response. LGP2, unable to activate the IFN response itself, modulates RIG-I and MDA5 signalling. HDV, a small RNA virus causing the most severe form of viral hepatitis, is sensed by MDA5. The mechanism underlying IFN induction and its effect on HDV replication is unclear. Here, we aimed to unveil the role of LGP2 and clinically relevant variants thereof in these processes.

Methods

RLRs were depleted in HDV susceptible HepaRG^NTCP cells and primary human hepatocytes. Cells were reconstituted to express different LGP2 versions. HDV and IFN markers were quantified in a time-resolved manner. Interaction studies among LGP2, MDA5, and RNA were performed by pull-down assays.

Results

LGP2 is essential for the MDA5-mediated IFN response induced upon HDV infection. This induction requires both RNA binding and ATPase activities of LGP2. The IFN response only moderately reduced HDV replication in resting cells but profoundly suppressed cell division-mediated HDV spread. An LGP2 variant (Q425R), predominating in Africans who develop less severe chronic hepatitis D, mediated detectably higher basal and faster HDV-induced IFN response as well as stronger HDV suppression. Mechanistically, LGP2 RNA binding was a prerequisite for the formation of stable MDA5–RNA complexes. MDA5 binding to RNA was enhanced by the Q425R LGP2 variant.

Conclusions

LGP2 is essential to mount an antiviral IFN response induced by HDV and stabilises MDA5–RNA interaction required for downstream signalling. The natural Q425R LGP2 is a gain-of-function variant and might contribute to an attenuated course of hepatitis D.

Impact and implications

HDV is the causative pathogen of chronic hepatitis D, a severe form of viral hepatitis that can lead to cirrhosis and hepatocellular carcinoma. Upon infection, the human immune system senses HDV and mounts an antiviral interferon (IFN) response. Here, we demonstrate that the immune sensor LGP2 cooperates with MDA5 to mount an IFN response that represses HDV replication. We mapped LGP2 determinants required for IFN system activation and characterised several natural genetic variants of LGP2. One of them reported to predominate in sub-Saharan Africans can accelerate HDV-induced IFN responses, arguing that genetic determinants, possibly including LGP2, might contribute to slower disease progression in this population. Our results will hopefully prompt further studies on genetic variations in LGP2 and other components of the innate immune sensing system, including assessments of their possible impact on the course of viral infection.

中文翻译：

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LGP2 变异对 MDA5 介导的干扰素反应激活和丁型肝炎病毒复制抑制的影响

背景与目标

视黄酸诱导基因 I (RIG-I) 样受体 (RLR)，包括 RIG-I、黑色素瘤分化相关蛋白 5 (MDA5) 和遗传生理学实验室 2 (LGP2)，感知病毒 RNA 以诱导抗病毒干扰素 (IFN) 反应。LGP2 本身无法激活 IFN 响应，它会调制 RIG-I 和 MDA5 信号。HDV 是一种小 RNA 病毒，可引起最严重的病毒性肝炎，可被 MDA5 检测到。IFN 诱导的潜在机制及其对 HDV 复制的影响尚不清楚。在这里，我们旨在揭示 LGP2 及其临床相关变体在这些过程中的作用。

方法

RLRs 在 HDV 易感的 HepaRG ^NTCP细胞和原代人肝细胞中被耗尽。细胞被重组以表达不同的 LGP2 版本。HDV 和 IFN 标记物以时间分辨的方式进行量化。LGP2、MDA5 和 RNA 之间的相互作用研究通过下拉分析进行。

结果

LGP2 对于 HDV 感染后诱导的 MDA5 介导的 IFN 反应至关重要。这种诱导需要 LGP2 的 RNA 结合和 ATPase 活性。IFN 反应仅适度减少了静息细胞中 HDV 的复制，但极大地抑制了细胞分裂介导的 HDV 传播。一种 LGP2 变体 (Q425R)，在发展不太严重的慢性丁型肝炎的非洲人中占主导地位，介导可检测到的更高的基础和更快的 HDV 诱导的 IFN 反应以及更强的 HDV 抑制。从机制上讲，LGP2 RNA 结合是形成稳定的 MDA5-RNA 复合物的先决条件。Q425R LGP2 变体增强了 MDA5 与 RNA 的结合。

结论

LGP2 对于启动由 HDV 诱导的抗病毒 IFN 反应至关重要，并稳定下游信号传导所需的 MDA5-RNA 相互作用。天然的 Q425R LGP2 是一种功能获得性变体，可能有助于减轻丁型肝炎的病程。

影响和启示

HDV 是慢性丁型肝炎的致病病原体，慢性丁型肝炎是一种严重的病毒性肝炎，可导致肝硬化和肝细胞癌。感染后，人体免疫系统会感知 HDV 并启动抗病毒干扰素 (IFN) 反应。在这里，我们证明免疫传感器 LGP2 与 MDA5 合作以启动抑制 HDV 复制的 IFN 反应。我们映射了 IFN 系统激活所需的 LGP2 决定因素，并表征了LGP2的几种天然遗传变异。据报道，其中一种在撒哈拉以南非洲人中占主导地位可以加速 HDV 诱导的 IFN 反应，认为遗传决定因素，可能包括LGP2，可能有助于减缓该人群的疾病进展。我们的结果有望促进对LGP2和先天免疫传感系统其他组成部分的遗传变异的进一步研究，包括评估它们对病毒感染过程的可能影响。