Unfolded protein response inhibitors cure group A streptococcal necrotizing fasciitis by modulating host asparagine

Abstract

Group A streptococcus (GAS) is among the top 10 causes of mortality from an infectious disease, producing mild to invasive life-threatening manifestations. Necrotizing fasciitis (NF) is characterized by a rapid GAS spread into fascial planes followed by extensive tissue destruction. Despite prompt treatments of antibiotic administration and tissue debridement, mortality from NF is still high. Moreover, there is no effective vaccine against GAS, and early diagnosis of NF is problematic because its clinical presentations are not specific. Thus, there is a genuine need for effective treatments against GAS NF. Previously, we reported that GAS induces endoplasmic reticulum (ER) stress to gain asparagine from the host. Here, we demonstrate that GAS-mediated asparagine induction and release occur through the PERK-eIF2α-ATF4 branch of the unfolded protein response. Inhibitors of PERK or integrated stress response (ISR) blocked the formation and release of asparagine by infected mammalian cells, and exogenously added asparagine overcame this inhibition. Moreover, in a murine model of NF, we show that the inhibitors minimized mortality when mice were challenged with a lethal dose of GAS and reduced bacterial counts and lesion size when mice were challenged with a sublethal dose. Immunohistopathology studies demonstrated that PERK/ISR inhibitors protected mice by enabling neutrophil infiltration into GAS-infected fascia and reducing the pro-inflammatory response that causes tissue damage. Inhibitor treatment was also effective in mice when started at 12 hours after infection. We conclude that host metabolic alteration induced by PERK or ISR inhibitors is a promising therapeutic strategy to treat highly invasive GAS infections.

Asparagine couples group AStreptococcalmetabolism to virulence

“…For determination of the lesion area, the dermonecrotic skin lesions were measured daily using a digital caliper (Bar Naor Ltd.). The lesion area was calculated with the formula A = (π/2)(length)(width) (Anand et al, 2021).…”

“…GAS delivers the toxins streptolysin S (SLS) and streptolysin O (SLO) into infected cells. These toxins cause endoplasmic reticulum (ER) stress, activating the PERK-eIF2α-ATF4 branch of the unfolded protein response (UPR) 18 . The activation of the PERK-eIF2α-ATF4 upregulates the host asparagine synthetase (ASNS) transcription 19 ; consequently, the Asn level is augmented in infected host cells 17,18 .…”

“…These toxins cause endoplasmic reticulum (ER) stress, activating the PERK-eIF2α-ATF4 branch of the unfolded protein response (UPR) 18 . The activation of the PERK-eIF2α-ATF4 upregulates the host asparagine synthetase (ASNS) transcription 19 ; consequently, the Asn level is augmented in infected host cells 17,18 . GAS utilizes the generated Asn to increase its growth rate and degree of virulence 17 .…”

“…GAS utilizes the generated Asn to increase its growth rate and degree of virulence 17 . By inhibiting the PERK-eIF2α-ATF4 pathway using specific inhibitors, we protected mice against invasive GAS diseases in murine models of soft tissue GAS infection 18 .…”

Dysregulation of stress-induced translational control by Porphyromonas gingivalis in host cells

“…Recent studies have reported that bacterial species may also target the host translational control machinery and ISR function (Reviewed in Knowles et al (20)). Several bacteria are known to activate host ISR stress response kinases upon infection including Shigella flexneri , Salmonella (37, 38), Pseudomonas aeruginosa (39), Mycobacterium tuberculosis (40), Yersinia pseudotuberculosis (41), Shiga toxin Escherishia coli (STEC) (42) and Group A Streptococci (43).…”