Nucleosomal dsDNA Stimulates APOL1 Expression in Human Cultured Podocytes by Activating the cGAS/IFI16-STING Signaling Pathway

Shamara E Davis,Atanu K Khatua,Waldemar Popik

doi:10.1038/s41598-019-51998-w

Shamara E Davis, Atanu K Khatua + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-51998-w

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Abstract

APOL1 alleles G1 and G2 are associated with faster progression to lupus nephritis (LN)-associated end-stage renal disease (LN-ESRD) in African Americans. Increased levels of type I interferons (IFNs) and nucleosome-associated double-stranded DNA (dsDNA) fragments (nsDNA) are the hallmark of this disease. Here, we identify cyclic GMP-AMP synthase (cGAS) and interferon-inducible protein 16 (IFI16) as the major DNA sensors in human immortalized podocytes. We also show that nsDNA triggers the expression of APOL1 and IFNβ via IRF3 activation through the cGAS/IFI16-STING pathway. We demonstrate that maximal APOL1 expression also requires the activation of type I IFN receptor (IFNAR) and STAT1 signaling triggered by IFNβ produced in response to nsDNA, or by exogenous IFNβ. Finally, we show that STAT1 activation is sufficient to upregulate IFI16, subsequently boosting APOL1 expression through a positive feedback mechanism. Collectively, we find that nsDNA-induced APOL1 expression is mediated by both IFNβ-independent and dependent signaling pathways triggered by activation of the cGAS/IFI16-STING pathway. We propose that simultaneous inhibition of STING and the IFNAR-STAT1 pathway may attenuate IFI16 expression, reduce IFI16-cGAS cross-talk, and prevent excessive APOL1 expression in human podocytes in response to nsDNA.

Highlights

Injury of kidney glomerular podocytes[8,9,10] is one of the hallmarks of lupus nephritis (LN) that develops in ~40–70% of patients with systemic lupus erythematosus (SLE)[11]
In view of recent reports demonstrating that the cross-talk between cyclic GMP-AMP synthase (cGAS) and interferon-inducible protein 16 (IFI16) regulates IFNβ expression in human keratinocytes[36] and human macrophages[37], it is conceivable that the strength of responses elicited by viral or synthetic DNA may differ from that triggered by nucleosomal double-stranded DNA (dsDNA) detected in lupus patients[19]
We found that mono-nucleosomal DNA fragments made up over 95% of the isolated nucleosomal dsDNA (nsDNA) (Fig. 1a)

Summary

Introduction

Injury of kidney glomerular podocytes[8,9,10] is one of the hallmarks of LN that develops in ~40–70% of patients with systemic lupus erythematosus (SLE)[11]. The presence of high levels of blood-circulating nucleosome-associated DNA fragments in lupus patients[19,20] suggests that the activation of DNA-sensing receptors may account for, at least in part, increased IFN expression[21] In this regard, the endosomal Toll-like receptor 9 (TLR9)[22], cytosolic cyclic GMP-AMP synthase (cGAS)[23], and interferon-inducible protein 16 (IFI16)[24] have been implicated in SLE25–29. We demonstrate that cGAS and IFI16 are the major DNA-sensing receptors in human immortalized AB8/13 podocytes that trigger the expression of APOL1 and IFNβ in response to cytosolic nsDNA via activation of the cGAS/IFI16-STING pathway. Findings from a previous report[35] suggest that even low levels of IFI16 may be sufficient to engage nsDNA and contribute to APOL1 expression

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