Autophagy during Severe Acute Respiratory Syndrome Coronavirus 2 Induced Leukocytoclastic Vasculitis: New Insights

View Large Image Figure ViewerDownload Hi-res image Download (PPT) The widespread severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has given rise to COVID-19 and its devastating consequences. Research studies report frequent dermatological manifestations, with at least 20% of patients with COVID-19 having cutaneous lesions (Magro et al., 2021Magro C. Nuovo G. Mulvey J.J. Laurence J. Harp J. Crowson A.N. The skin as a critical window in unveiling the pathophysiologic principles of COVID-19.Clin Dermatol. 2021; 39: 934-965Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar). Reports of this population note a wide range of cutaneous vasculitis, including cutaneous small vessel vasculitis, also known as leukocytoclastic vasculitis (LCV)."The implication of LC3B, LC3C, and LL-37 in COVID-19-associated skin vasculopathies could open novel avenues to therapeutic targets." "The implication of LC3B, LC3C, and LL-37 in COVID-19-associated skin vasculopathies could open novel avenues to therapeutic targets." Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar recently reported new data investigating the mechanisms of vascular injury and the potential causality of SARS-CoV-2 spike protein in skin lesions. From a cohort of 4 patients positive for SARS-CoV-2 associated with LCV, compared with 3 controls without COVID-19 disease, the investigators characterized the microvascular changes in samples associated with COVID-19–induced vasculitis. To explore the mechanism of vascular injury and to investigate the causality of direct viral presence in the skin, they performed histological analyses with ultrastructural characterization of endothelial cells. Interestingly, they found extensive SARS-CoV-2 spike protein deposition in microvascular endothelial cells that colocalized with the autophagosome proteins LC3B and LC3C—markers of autophagy. The researchers concluded that massive spike protein deposition in autophagosomes occurs during SARS-CoV-2–associated cutaneous vasculitis.Clinical Implications•This study provides insight into a connection between COVID-19 and cutaneous lesions.•It spells out the evidence relating the virus to the skin manifestations.•It demonstrates that LC3B, LC3C, and LL-37 in COVID-19–associated skin vasculopathies could open novel avenues to therapeutic targets. •This study provides insight into a connection between COVID-19 and cutaneous lesions.•It spells out the evidence relating the virus to the skin manifestations.•It demonstrates that LC3B, LC3C, and LL-37 in COVID-19–associated skin vasculopathies could open novel avenues to therapeutic targets. LCV, reported in 1.8% of all skin findings in patients with COVID-19 (Kaya et al., 2020Kaya G. Kaya A. Saurat J.H. Clinical and histopathological features and potential pathological mechanisms of skin lesions in COVID-19: review of the literature.Dermatopathology (Basel). 2020; 7: 3-16Crossref PubMed Google Scholar), is a type of small-vessel vasculitis characterized by inflammation of the small blood vessels. Often associated with an immune response, various factors can trigger it, including viral infections and drugs. Immune complex aggregates in the postcapillary venules, infiltration of polymorphonuclear cells, fibrinoid necrosis, and leukocytoclasis histologically characterize LCV. Reports note that vasculopathy without true vasculitic changes on histology develops in a minority of cases, mostly in patients with severe or critical COVID-19 (Maronese et al., 2022Maronese C.A. Zelin E. Avallone G. Moltrasio C. Romagnuolo M. Ribero S. et al.Cutaneous vasculitis and vasculopathy in the era of COVID-19 pandemic.Front Med (Lausanne). 2022; 9996288Google Scholar). The pathogenic mechanisms of cutaneous vasculitis in COVID-19 are not fully elucidated. Although the role of a hyperactive immune response, complement activation, and microvascular injury is in question, it appears to result from endothelial injury due to pauci-immune thromboembolic mechanisms. Previous beliefs attributed endothelial damage to direct viral infection. However, recent research suggests that indirect mechanisms of endothelial damage may also be involved in the pathogenesis of COVID-19 vasculopathy, including low endothelial cell expression of angiotensin-converting enzyme 2 (ACE2) and resistance to infection with SARS CoV-2 (Maronese et al., 2022Maronese C.A. Zelin E. Avallone G. Moltrasio C. Romagnuolo M. Ribero S. et al.Cutaneous vasculitis and vasculopathy in the era of COVID-19 pandemic.Front Med (Lausanne). 2022; 9996288Google Scholar). Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar performed histological analysis and electron microscopy for ultrastructural characterization of capillaries. They found that vascular endothelial damage and the associated inflammatory pattern were similar in all 4 SARS-CoV-2–associated vasculitic skin lesions and closely simulated the pathology of classical LCV. They observed vasocentric lymphohistiocytic and neutrophilic inflammatory infiltrates, neutrophilic nuclear dust, erythrocyte extravasation, and capillary wall degeneration with fibrin deposition. The viral surface spike protein (S) mediates SARS-CoV-2 entry into cells. To fulfill its function, SARS-CoV-2 S protein binds to its receptor ACE2 through its receptor binding domain and is activated by human proteases, allowing the virus to infect the cell. Although investigators have reported the detection of SARS-CoV-2 viral particles in skin and sweat glands (Cazzato et al., 2022Cazzato G. Cascardi E. Colagrande A. Foti C. Stellacci A. Marrone M. et al.SARS-CoV-2 and skin: new insights and perspectives.Biomolecules. 2022; 12: 1212Crossref Scopus (9) Google Scholar), it is still uncertain whether spike protein deposition is attributable to direct infection by SARS-CoV-2 or the consequence of circulating spike protein from other organs leading to microvascular endothelial cells. Magro et al., 2021Magro C. Nuovo G. Mulvey J.J. Laurence J. Harp J. Crowson A.N. The skin as a critical window in unveiling the pathophysiologic principles of COVID-19.Clin Dermatol. 2021; 39: 934-965Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar reported the presence of COVID-19 spike glycoproteins in the interalveolar septa in 5 cases. They also observed cutaneous microvasculature in 2 cases, suggesting the presence of SARS CoV-2 spike protein in both endothelial and eccrine cells of skin lesions (Magro et al., 2021Magro C. Nuovo G. Mulvey J.J. Laurence J. Harp J. Crowson A.N. The skin as a critical window in unveiling the pathophysiologic principles of COVID-19.Clin Dermatol. 2021; 39: 934-965Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar). The authors (Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar) did not detect SARS-CoV-2 virus particles in the skin by electron microscopy. However, Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar did observe abundant SARS-CoV-2 spike protein in both the cytoplasm and in/around the nucleus of endothelial cells of dermal capillaries. To date, there is no real evidence of active viral replication in most microvascular endothelium, despite the localization of viral capsid protein, specifically in endothelial cells of small dermal vessels (Magro et al., 2021Magro C. Nuovo G. Mulvey J.J. Laurence J. Harp J. Crowson A.N. The skin as a critical window in unveiling the pathophysiologic principles of COVID-19.Clin Dermatol. 2021; 39: 934-965Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar). Neutrophils are one of the most effective immune cells in the defense against external pathogens; they play an important role in pathogen clearance and have specific antiviral mechanisms. NETosis, a form of cell death primarily caused by neutrophils, is associated with the creation of extracellular neutrophil traps (NETs). NETs are composed of DNA fibers or nuclear chromatin that encapsulate cytosolic granule proteins and histones in a depolymerized reticulated form to trap and eliminate pathogens (Zhang et al., 2023Zhang R. Sun C. Han Y. Huang L. Sheng H. Wang J. et al.Neutrophil autophagy and NETosis in COVID-19: perspectives.Autophagy. 2023; 19: 758-767Crossref Scopus (3) Google Scholar). Autophagy—the conserved autodegradation process in neutrophils—plays a critical role in neutrophil phagocytosis of pathogens. Autophagy is a catabolic process that isolates damaged cellular components as well as invasive microbes, isolating them from the rest of the cell, forming autophagosomes, and delivering them to the lysosomes for degradation. This cellular eukaryotic process is essential for cell survival, homeostasis, and immunity (Resnik et al., 2023Resnik R. Lopez Mingorance F. Rivera F. Mitchell F. Gonzalez C.D. Vaccaro M.I. Autophagy in inflammatory response against SARS-CoV-2.Int J Mol Sci. 2023; 24: 4928Crossref Scopus (3) Google Scholar). SARS-CoV-2 viruses can affect both cellular metabolism and autophagy pathways. This leads to the accumulation of important metabolites in infected cells, including the autophagy marker microtubule-associated proteins (LC3B). LC3 plays a crucial role in the overall autophagy process. LC3B acts as an RNA-binding protein that causes mRNA interference during autophagy. Different tissues and cell types ubiquitously express LC3B. Researchers have implicated LC3C, which is expressed at lower levels, in virus-induced autophagosome formation (Delorme-Axford and Klionsky, 2020Delorme-Axford E. Klionsky D.J. Highlights in the fight against COVID-19: does autophagy play a role in SARS-CoV-2 infection?.Autophagy. 2020; 16: 2123-2127Crossref PubMed Scopus (24) Google Scholar). Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar focused on LC3B and LC3C—protein markers for autophagy—to determine whether they could also observe changes in LC3-associated autophagy in cutaneous vasculitis in the setting of COVID-19 infection. They observed that LC3B was more prominent in the areas of vascular-associated cells, whereas LC3C was more evident directly in the endothelial cells of the small cutaneous vessels than in healthy skin, where neither LC3B nor LC3C were detectable in any vascular or perivascular structures. The cathelicidin antimicrobial peptide LL-37 belongs to the family of host defense peptides. Neutrophilic granulocytes release LL-37, which plays an important role in innate immunity and is known for its antiviral activity. Some researchers reported elevated plasma levels of LL-37 during severe cases of COVID-19 with clinical hypercoagulation manifestations (Duan et al., 2022Duan Z. Zhang J. Chen X. Liu M. Zhao H. Jin L. et al.Role of LL-37 in thrombotic complications in patients with COVID-19.Cell Mol Life Sci. 2022; 79: 309Crossref Scopus (10) Google Scholar). Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar reported that LL-37 peptide was predominantly present in the cytoplasm in COVID-19–associated cases rather than nuclear in nonrelated COVID-19 cases, therefore suggesting that cases of SARS-CoV-2–related vasculitis might not directly infect the endothelia. In a review by Aloul et al., 2022Aloul K.M. Nielsen J.E. Defensor E.B. Lin J.S. Fortkort J.A. Shamloo M. et al.Upregulating human cathelicidin antimicrobial peptide LL-37 expression may prevent severe COVID-19 inflammatory responses and reduce microthrombosis.Front Immunol. 2022; 13880961Crossref Scopus (14) Google Scholar, the authors highlighted that LL-37 plays an important role in the clearance of NETs and helps in the in vitro endocytosis of extracellular DNA by dendritic cells through DNA aggregation. Furthermore, they suggested that enhancing the expression of the human cathelicidin antimicrobial peptide LL-37 could potentially mitigate severe inflammatory reactions related to COVID-19 and decrease the incidence of microthrombosis. Although previous research has suggested that virus-dependent and immune-mediated mechanisms play an important role in COVID-19–related LCV, it has not yet clearly identified the specific molecular and cellular pathways responsible for endothelial damage in patients with COVID-19. The study reported by Gawaz et al., 2024Gawaz A. Schindler M. Hagelauer E. Blanchard G. Riel S. Vollert A. et al.SARS-CoV-2-induced vasculitic skin lesions are associated with massive spike protein depositions in autophagosomes.J Invest Dermatol. 2024; 144: 369-377.e4Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar provides new evidence for the concept of autophagosome-associated deposition of SARS-CoV2 spike proteins. These findings contribute to a better understanding of the pathogenesis of virus-associated damage during cutaneous vasculopathy. The implication of LC3B, LC3C, and LL-37 in COVID-19–associated skin vasculopathies could open novel avenues to therapeutic targets (Figure 1). However, researchers should exercise caution owing to the small sample size studied and the timing of the investigations, which were late in the course of the disease. We need further prospective studies in larger cohorts to confirm these findings. Nesrine Brahimi: http://orcid.org/0009-0007-0799-852X Vincent Piguet: http://orcid.org/0000-0001-6079-4517 VP has no personal financial ties with any pharmaceutical company. He undertakes advisory work for Pfizer, AbbVie, Janssen, UCB, Novartis, Almirall, and Celgene. He has received honoraria from Kyowa Kirin. In his role as Department Division Director of Dermatology at the University of Toronto, VP has received departmental support from AbbVie, Bausch Health, Celgene, Janssen, LEO Pharma, Lilly, NAOS, Novartis, Pfizer, Pierre-Fabre, and Sanofi in the past 36 months. NB has received clinical fellowship funding from AbbVie Canada Grants. No funding was received for the preparation of this commentary. SARS-CoV-2–Induced Vasculitic Skin Lesions Are Associated with Massive Spike Protein Depositions in AutophagosomesJournal of Investigative DermatologyVol. 144Issue 2PreviewIn patients infected with severe acute respiratory syndrome coronavirus 2, vasculopathic changes of the skin are associated with a severe prognosis. However, the pathogenesis of this vasculopathy is not conclusively clarified. In this study, 25 prospectively collected skin samples from patients with COVID-19–related skin lesions were examined for vasculopathic changes and, in case of vasculitis, were further analyzed with electron microscopy and immunohistochemistry. Vasculopathy was observed in 76% of all COVID-19–related inflammatory skin lesions.