Brain immune cells undergo cGAS/STING-dependent apoptosis during herpes simplex virus type 1 infection to limit type I IFN production
Line S. Reinert, … , Georges MGM Verjans, Søren R. Paludan
Line S. Reinert, … , Georges MGM Verjans, Søren R. Paludan
Published September 29, 2020
Citation Information: J Clin Invest. 2021;131(1):e136824. https://doi.org/10.1172/JCI136824.
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Research Article Immunology Infectious disease

Brain immune cells undergo cGAS/STING-dependent apoptosis during herpes simplex virus type 1 infection to limit type I IFN production

Abstract

Protection of the brain from viral infections involves the type I IFN (IFN-I) system, defects in which render humans susceptible to herpes simplex encephalitis (HSE). However, excessive cerebral IFN-I levels lead to pathologies, suggesting the need for tight regulation of responses. Based on data from mouse models, human HSE cases, and primary cell culture systems, we showed that microglia and other immune cells undergo apoptosis in the HSV-1–infected brain through a mechanism dependent on the cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) pathway, but independent of IFN-I. HSV-1 infection of microglia induced cGAS-dependent apoptosis at high viral doses, whereas lower viral doses led to IFN-I responses. Importantly, inhibition of caspase activity prevented microglial cell death and augmented IFN-I responses. Accordingly, HSV-1–infected organotypic brain slices or mice treated with a caspase inhibitor exhibited lower viral load and an improved infection outcome. Collectively, we identify an activation-induced apoptosis program in brain immune cells that downmodulates local immune responses.

Authors

Line S. Reinert, Ahmad S. Rashidi, Diana N. Tran, Georgios Katzilieris-Petras, Astrid K. Hvidt, Mette Gohr, Stefanie Fruhwürth, Chiranjeevi Bodda, Martin K. Thomsen, Mikkel H. Vendelbo, Ahmad R. Khan, Brian Hansen, Petra Bergström, Lotta Agholme, Trine H. Mogensen, Maria H. Christensen, Jens R. Nyengaard, Ganes C. Sen, Henrik Zetterberg, Georges MGM Verjans, Søren R. Paludan

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Figure 6

HSV-1 infection induces cGas/STING-dependent apoptosis in microglia.

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HSV-1 infection induces cGas/STING-dependent apoptosis in microglia. (A ...
(A and C) Analysis of apoptosis in primary murine microglia after treatment with mock or HSV-1 (15 MOI) for 6 or 8 hours by flow cytometry using annexin V antibody and PI staining. Apoptosis inducer raptinal (10 μM, 45 minutes) was used as positive control. (B) Lysates from microglia treated as in A were analyzed for caspase-3/7 activity 8 hours after infection. (D–F) Microglia were infected as in A for 6 hours and the expression of HSV-1 gB, Ifnβ, and Puma was analyzed by real-time qPCR. Values were normalized to β-actin and presented as mean ± SEM. (G) iPSC-derived microglia were infected with HSV-1 (MOI 5 and 15) or treated with cGAMP and analyzed for caspase-3/7 activity 12 hours later. (H and I) WT primary murine microglia were infected with 5 or 15 MOI for 12 hours and caspase-3/7 activity or Ifn-β mRNA levels were analyzed as in B and E, respectively. (J and K) The microglia cell line BV2 was treated with either HSV-1 (15 MOI) for 8 hours or raptinal (10 μM) for 15 minutes. The cytosolic and mitochondrial fractions were isolated and samples were subjected to immunoblotting with antibody against cytochrome c, COX IV (mitochondria marker), or vinculin. Densitometry was used to quantify the cytochrome c release relative to vinculin and shown in K. (L) Cellular model of IFN versus apoptosis response in HSV-1–infected microglia. All figures represent at least 3 independent experiments, n = 4–6 per group (A–I) and n = 1 (K); P values were calculated by 1-way ANOVA with Tukey’s multiple-comparison test (A and G) and 2-tailed Student’s t test (B–F, H, and I). P > 0.05 (NS, not significant); *0.01 < P < 0.05; **0.001 < P < 0.01; ***0.0001 < P < 0.001; ****P < 0.0001.