Coronavirus infection (SARS-CoV-2) in obesity and diabetes comorbidities: is heat shock response determinant for the disease complications?

Abstract

Chronic inflammation is involved in the pathogenesis of several metabolic diseases, such as obesity and type 2 diabetes mellitus (T2DM). With the recent worldwide outbreak of coronavirus disease (SARS-CoV-2), it has been observed that individuals with these metabolic diseases are more likely to develop complications, increasing the severity of the disease and a poorer outcome. Coronavirus infection leads to the activation of adaptive and innate immune responses, resulting in massive inflammation (to so called cytokine storm), which in turn can lead to damage to various tissues, septic shock and multiple organ failure. Recent evidence suggests that the common link between metabolic diseases and SARS-CoV-2 is the inflammatory response (chronic/low-grade for metabolic diseases and acute/intense in coronavirus infection). However, the ability of the infected individuals to resolve the inflammation has not yet been explored. The heat shock response (HSR), an important anti-inflammatory pathway, is reduced in patients with metabolic diseases and, consequently, may impair inflammation resolution and control in patients with SARS-CoV-2, thus enabling its amplification and propagation through all tissues. Herein, we present a new hypothesis that aims to explain the increased severity of SARS-CoV-2 infection in people with metabolic diseases, and the possible benefits of HSR-inducing therapies to improve the inflammatory profile in these patients.

Keywords: Heat shock response; Inflammation; Metabolic diseases; SARS-CoV-2.

Fig. 1

Heat shock response and HSP70 function. The Activation of the heat shock response after non-lethal stress. (I) At rest HSF-1 is inactive in a monomeric state bonded with the cytosolic HSP70s, located in the cytosol. P: Functional Proteins. (II) Under stress conditions and in the presence of denatured proteins (DP), HSP70 releases HSF-1 and subsequently binds to denatured proteins, acting as chaperones (aiding protein refolding) and releasing HSF. Serine-phosphorylation and trimerisation of HSF-1 induces enhanced HSF-1 DNA binding affinity. The binding of the trimeric HSF to HSE initiates the transcription of the HSP mRNA. Additionally, SIRT1 prolongs HSF1 binding to the promoters of heat shock genes by maintaining HSF1 in a deacetylated form. (III) After recovery from stress, HSP70 rebinds to HSF-1 so exerting an inhibitory effect on HSF-1/HSE binding. Overall, stress adaptation is associated with increased levels of HSP70

Fig. 2

Heat shock response in healthy and in insulin resistant state. In insulin sensitive state, activation of insulin signalling will lead in inhibition of the enzyme GSK-3β (by phosphorylation). In this case, activation of HSR, when stimulated, is normal and HSP72 can maintain NF-κB inhibition, thus an inflammatory balance. Obesity (adipose tissue expansion) and physical inactivity initiates a chronic low-grade inflammation that spread to all tissues. The inflammatory mediators (cytokines, TLR ligands and others) can induce the activation of NF-κB and JNK, leading to ROS/RNS overproduction (by increase activity and expression of inflammatory enzymes) and inhibition of insulin signalling. In the presence of insulin resistance, GSK-3β become activated and inhibits HSF1 activity and expression, resulting in a blunted HSR. Under this circumstance, no inhibition over NF-κB results in amplification of inflammation and no resolution, causing a vicious inflammatory cycle. Heat therapy (hot water immersion or sauna) and exercise can activate HSR and ameliorates insulin signalling and inflammation. Two potential alternative therapies that may be applied to restore HSR and reduce inflammation in SARS-CoV-2 infected patients is the rationale use of antipyretic drugs (allowing increases in temperature, thus improving HSR) and the use of HSR activator drugs, such as the BGP-15

Fig. 3

Heat shock response test in blood of SARS-CoV-2 patients. After harvesting, whole blood is immediately incubated at two different temperatures: 37 °C (control) and 42 °C (heat stressed) for 2 h in water bath (with gentle mix every 15 min). After the incubation, total blood is centrifuged to isolate plasma/serum and PBMC through density gradient separation. Then, plasma can be used for the direct analysis of extracellular HSP72 (eHSP72) while PBMC can be prepared for the measurement of intracellular (iHSP72). The PMBC must be washed and treated to ensure the absence of erythrocytes. PBMC are resuspended in RPMI 1640 medium (pH 7,4 supplemented with 2% NaHCO₃, 10% bovine calf serum, 100 U/mL penicillin and 100 µg/mL streptomycin), seeded in a 24-well flat bottom plate (1 × 106 cells/well) and placed in an incubator for 6 h (37 °C in a 5% CO₂), in order to recover from the HS and reach the peak of HSP70 expression. Cells are then removed from the incubator, appropriated lysed and the total content of proteins prepared for western Blot analysis. The difference between concentration at 37 °C and 42 °C is used as HSR index