Marcello Baroni

Emerging and re-emerging RNA viruses frequently present with clinical phenotypes that extend beyond classical organ tropism and include vascular leakage, platelet dysregulation, coagulation imbalance, microvascular injury, and thromboinflammation. SARS-CoV-2, flaviviruses, and hantaviruses provide three complementary models of virus-induced vascular disease. This narrative review compares these viruses through a shared endothelial–coagulative framework and proposes four partially overlapping vascular programs: endothelial activation, endothelial barrier failure, coagulation activation, and platelet quantitative or qualitative dysfunction. These programs are intended as a conceptual synthesis of convergent clinical, pathological, and experimental evidence rather than as a quantitative classification system. The framework is used not only to organize known mechanisms, but also to generate testable predictions for cross-virus biomarker panels, organ-specific endothelial models, and phenotype-guided clinical studies. Severe COVID-19 illustrates inflammation-driven endothelial activation, platelet–leukocyte interactions, complement amplification, NETosis, and immunothrombosis. Within the flavivirus group, DENV is used as the principal model for systemic vascular leakage, thrombocytopenia, and hemorrhagic risk; selected non-dengue flaviviruses illustrate how shared endothelial, platelet, and coagulation modules are redirected toward placental dysfunction (ZIKV), neuroinvasion (WNV and JEV), or hepatic failure and coagulopathy (YFV). Hantavirus infections provide a distinctive model of capillary leak syndrome in which non-lytic endothelial infection, immune-mediated injury, and permeability signaling converge on renal and pulmonary microvascular beds. A comparative view suggests that thrombotic, hemorrhagic, and leaky phenotypes are not mutually exclusive categories, but different outcomes of overlapping vascular programs shaped by viral tropism, vascular-bed specialization, immune activation, and host susceptibility.

Natural killer (NK) cells are central to antiviral immunity through a balance of activating and inhibitory receptors, including killer immunoglobulin-like receptors (KIRs). We have previously observed that an increased frequency of the inhibitory receptor KIR2DL2 and its ligand HLA-C1 is associated with heightened susceptibility to human herpesvirus (HHV) infection, supporting a role for KIR-mediated NK cell regulation in host–virus interactions. We investigated whether the co-infection of SARS-CoV-2 and human herpesvirus 6 (HHV-6) might be connected to the expression of KIR2DL2/HLA-C1. We analyzed 110 SARS-CoV-2-positive subjects and 109 SARS-CoV-2-negative subjects for the KIR2DL2 and HLA-C1 genotype and for HHV-6A/B reactivation in plasma samples. SARS-CoV-2-positive subjects showed a significantly higher frequency of the KIR2DL2/HLA-C1 haplotype and increased reactivation of HHV-6A. Among deceased and comorbid patients, the co-occurrence of the KIR2DL2/HLA-C1 haplotype and HHV-6A DNAemia was more frequent, particularly in those with cardiovascular disorders. These findings suggest that the KIR2DL2/HLA-C1 haplotype might promote NK cell inhibition, facilitating HHV-6A persistence and contributing to immune dysregulation during SARS-CoV-2 infection. The combined presence of KIR2DL2/HLA-C1 and HHV-6A may, therefore, represent a molecular signature of COVID-19 outcomes.

Background: Coagulation decompensation is one of the complications most frequently encountered in COVID-19 patients with a poor prognosis or long-COVID syndrome, possibly due to the persistence of SARS-CoV-2 infection in the cardiovascular system. To date, the mechanism underlying the alteration of the coagulation cascade in COVID-19 patients remains misunderstood and the anticoagulant protein S (PROS1) has been described as a potential risk factor for complications related to COVID-19, due to PLpro SARS-CoV-2 enzyme proteolysis. Methods: Biopsies and blood samples were collected from SARS-CoV-2 positive and negative swab test subjects with coagulopathies (peripheral arterial thrombosis), and SARS-CoV-2 presence, ACE2 and CD147 expression, and plasmatic levels of PROS1 were evaluated. Results: We reported a significant decrease of plasmatic PROS1 in the coagulopathic SARS-CoV-2 swab positive cohort, in association with SARS-CoV-2 in situ infection and CD147 peculiar expression. These data suggested that SARS-CoV-2 associated thrombotic/ischemic events might involve PROS1 cleavage by viral PLpro directly in the site of infection, leading to the loss of its anticoagulant function. Conclusions: Based on this evidence, the identification of predisposing factors, such as CD147 increased expression, and the use of PLpro inhibitors to preserve PROS1 function, might be useful for COVID-19 coagulopathies management.

The individual roles of cholesterol pathway biomarkers (CPB) and hemostasis inhibitors with neuroimaging outcomes were previously investigated in multiple sclerosis (MS). The purpose of this extension study was to investigate potential crosstalk between plasma CPB [total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and apolipoproteins (Apo) ApoA-I, ApoAII, ApoB, ApoC-II and ApoE] and hemostasis inhibitors [heparin cofactor-II (HCII), protein C (PC), protein S (PS), thrombomodulin, ADAMTS13 and PAI-1] in a cohort of 127 MS patients, and 40 healthy individuals (HI). The associations were assessed with regressions. In MS patients, HCII was positively associated with TC, LDL-C, HDL-C and ApoA-I (p=0.028, 0.027, 0.002 and 0.027, respectively) but negatively associated with ApoCII (p=0.018). PC was positively associated with ApoC-II (p=0.001) and ApoB (p=0.016) whereas PS was associated with TC (p=0.024) and ApoE (p=0.003) in MS. The ApoC-II associations were not observed in HI. The negative association between ApoC-II and HCll was an exception amongst other positive associations between CPB and hemostasis inhibitors in MS. CPB do not modulate the PC associations with neurodegeneration in MS.

The anticoagulant protein S (PS) binds phospholipids with very high affinity, but PS interaction with lipoproteins and lipidrich atherosclerotic plaques remains still poorly defined. We investigated PS in plasma lipoproteins and in atherosclerotic plaques from ten patients undergoing endarterectomy. PS was detected by Western blotting after exposure of the necrotic core to liposomes and was found to maintain its ability to bind phosphatidylserine micelles. The amounts of PS bound to low/very low-density lipoproteins in patient’ plasmas were higher and more variable than those detected in healthy subjects. A direct correlation between bound PS and low-density lipoproteins (LDL), plasma levels was found only in patients (r=0.921, p<0.001), thereby leading to hypothesize that the PS-phospholipids binding may increase by oxidative processes of LDL in atherosclerotic patients. The presence of the PS into the necrotic core of atherosclerotic plaques and on the surface of lipoproteins, particularly the atherogenic LDL, suggests a LDL-based delivery of PS to the atherosclerotic plaques and emphasizes the deep link between plasma lipids and coagulation in cardiovascular diseases.

Aiming at exploring vascular components in multiple sclerosis (MS) with brain outflow disturbance, we combined transcriptome analysis in MS internal jugular vein (IJV) wall with WES in MS families with vertical transmission of disease. Main results were the differential expression in IJV wall of 16 MS-GWAS genes and of seven genes (GRIN2A, GRIN2B, IL20RB, IL26, PER3, PITX2, and PPARGC1A) not previously indicated by GWAS but encoding for proteins functionally interacting with MS candidate gene products. Strikingly, 22/23 genes have been previously associated with vascular or neuronal traits/diseases, nine encoded for transcriptional factors/regulators and six (CAMK2G, GRIN2A, GRIN2B, N1RD1, PER3, PPARGC1A) for circadian entrainment/rhythm components. Among the WES low-frequency (MAF ≤ 0.04) SNPs (n = 7) filtered in the 16 genes, the NR1D1 rs17616365 showed significantly different MAF in the Network for Italian Genomes affected cohort than in the 1000 Genome Project Tuscany samples. This pattern was also detected in five nonintronic variants (GRIN2B rs1805482, PER3 rs2640909, PPARGC1A rs2970847, rs8192678, and rs3755863) in genes coding for functional partners. Overall, the study proposes specific markers and low-frequency variants that might help (i) to understand perturbed biological processes in vascular tissues contributing to MS disease, and (ii) to characterize MS susceptibility genes for functional association with disease-pathways.

(1) Background: Congenital factor (F) VII deficiency is caused by mutations in the F7 gene. Patients with modest differences in FVII levels may display large differences in clinical severity. The variant p.A354V-p.P464Hfs is associated with reduced FVII antigen and activity. The aim of the study was to investigate the clinical manifestation of this variant and the underlying molecular mechanisms. (2) Methods: Analyses were conducted in 37 homozygous patients. The recombinant variant was produced in mammalian cells. (3) Results: We report a large variation in clinical phenotypes, which points out genetic and acquired components beyond F7 mutations as a source of variability. In contrast, patients displayed similarly reduced FVII plasma levels with antigen higher than its activity. Comparative analysis of the recombinant variant and of plasma samples from a subset of patients indicated the presence of an elongated variant with indistinguishable migration. Treatment of cells with the chemical chaperone 4-phenylbutyrate (4-PBA) improved the intracellular trafficking of the variant and increased its secretion to the conditioned medium up to 2-fold. However, the effect of 4-PBA on biological activity was marginal. (4) Conclusions: Chemical chaperones can be used as biochemical tools to study the intracellular fate of a trafficking-defective FVII variant.

Congenital coagulation factor (F) VII deficiency is a rare bleeding disorder caused by mutations in the F7 gene. The missense factor FVII variant p.Q160R is the disease-causing mutation in all Norwegian FVII deficient patients and results in reduced biological activity and antigen levels of FVII in patient plasma. Previous in vitro studies on this variant demonstrated impaired intracellular trafficking and reduced secretion, possibly due to protein misfolding. The aim of the study was therefore to assess the impact of chemical chaperones on cellular processing and secretion of this variant using a cell model based on overexpression of the recombinant protein. Through screening of compounds, we identified 4-phenylbutyrate (4-PBA) to increase the secretion of recombinant (r) FVII-160R by ~ 2.5-fold. Additionally, treatment with 4-PBA resulted in a modest increase in specific biological activity. Intracellular localization studies revealed that upon treatment with 4-PBA, rFVII-160R was secreted through Golgi and Golgi reassembly-stacking protein (GRASP)-structures. The present study demonstrates that the chemical chaperone 4-PBA, restores intracellular trafficking and increases the secretion of a missense FVII variant with functional properties in the extrinsic coagulation pathway.