Study reveals how the JAK inhibitor lowers ACE2 expression and viral entry in individuals with a genetic risk variant linked to autoimmune diseases.

Study: Tofacitinib Mitigates the Increased SARS-CoV-2 Infection Susceptibility Caused by an IBD Risk Variant in the PTPN2 Gene. Image Credit: GB.JSTOCK / Shutterstock.com

A recent study published in Cellular and Molecular Gastroenterology and Hepatology reports the ability of the monoclonal antibody tofacitinib to reduce infection risk with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in individuals who are deficient in the tyrosine phosphatase non-receptor type 2 (PTPN2) protein.

SARS-CoV-2 and JAK inhibitors

Since its emergence at the end of 2019, SARS-CoV-2, which is the virus that causes the coronavirus disease 2019 (COVID-19), has infected hundreds of millions of individuals throughout the world, over seven million of whom succumbed to this infection. Risk factors for severe COVID-19 include advanced age and certain comorbidities including type 2 diabetes mellitus, hypertension, and autoimmune diseases.

The SARS-CoV-2 spike (S) protein mediates its attachment and entry into host cells by binding to the angiotensin converting enzyme (ACE2) receptor. The expression of ACE2, which is present at high concentrations on both lung and intestinal epithelial cells, is directly related to interferon (IFN)- Janus kinase (JAK)- signal transducer and activator of transcription (STAT) signaling pathway.

PTPN2 protects the gut barrier from inflammation-linked disruption by deactivating several JAK-STAT mediators. The rs1893217 variant of PTPN2 is a loss-of-function variant that increases the risk of autoimmune inflammation including inflammatory bowel disease (IBD), rheumatoid arthritis (RA), and type 1 diabetes mellitus.

Tofacitinib, an inhibitor of both JAK1 and JAK3, is currently approved for the treatment of rheumatoid arthritis (RA) and ulcerative colitis with the IBD subtype. Previously, the researchers of the current study reported that tofacitinib protects the intestinal barrier against destructive inflammation in the context of PTPN2 deficiency.

About the study

Patients with IBD who carried the rs1893217 variant of PTPN2 were genetically sampled for intestinal and peripheral blood mononuclear cells. Samples from PTPN2-deficient mice were also obtained. ACE2 expression in these samples was compared with that in human intestinal and lung epithelial cells with and without this risk variant.

The effect of the PTPN2 gene on ACE2 expression was assessed, along with evaluating the uptake of SARS-CoV-2 and virus-like particles (VLPs) carrying the SARS-CoV-2 spike protein.

PTPN2 regulates ACE2 levels and viral entry

PTPN2 deficiency by deletion, knockdown, or the presence of the rs1893217 variant increased ACE2 expression. As a result, PTPN2 deficiency promoted cell entry of both SARS-CoV-2 and VLPs bearing SARS-CoV-2 spike protein, thereby increasing infection rates in epithelial and immune cells.

The use of an ACE2 inhibitor prevented VLP uptake in PTPN2-deficient cells, thus demonstrating that viral spike uptake was mediated by ACE2.

IBD patients did not exhibit any change in ACE2 levels, irrespective of the presence of inflammation.

Inflammation does not promote ACE2 expression per se, but elevated ACE2 levels in patients or mice with reduced PTPN2 activity are indeed a consequence of PTPN2 deficiency.”

Gamma-interferon increases ACE2 levels and spike uptake

IFN-γ treatment led to higher ACE2 expression with a consequent rise in spike protein uptake that was enhanced in PTPN2-deficient cells. Comparatively, ACE2 expressed was suppressed by STAT1 silencing in these cells, thus demonstrating that PTPN2 deficiency increases ACE2 expression and viral entry through a STAT1-dependent mechanism.

STAT1/3 are PTPN2 substrates that are directly dephosphorylated by this protein; therefore, STAT inhibition may reduce viral entry by regulating ACE2 levels. 

IBD patients with the PTPN2 loss-of-function SNP rs1893217 variant exhibited higher ACE2 transcription and translation activity. VLP entry was also greater in these individuals as compared to non-carriers.

JAK-STAT signaling and ACE2 overexpression

Increased ACE2 expression in PTPN2-deficient cells is due to greater signaling in the JAK-STAT pathway in response to inflammatory cytokines such as IFN-γ. Treatment with tofacitinib, a pan-JAK inhibitor, reversed this sequence of events in PTPN2-deficient cells, which led to reduced ACE2 expression and viral entry.

There was no change in soluble ACE2 levels, thus indicating that viral shedding or release were unaffected. These effects were observed in both intestinal and respiratory epithelial cells, both of which are often affected during SARS-CoV-2 infection. Therefore, treatment with tofacitinib has the potential to reduce viral entry at the primary entry sites of SARS-CoV-2.

Tofacitinib decreased viral entry in both variant carriers and non-carriers, thus suggesting that this agent reduces ACE2 expression in host cells, rather than  through the inhibition of ACE2 release.

Our findings uncover a novel risk biomarker for increased expression of the SARS-CoV-2 receptor and viral entry, and identify a clinically approved therapeutic agent to mitigate this risk.”