SARS-CoV-2 infectious type-II alveolar lung cells show senescence

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Using monoclonal antibodies against acute coronavirus spike syndrome 2 (SARS-CoV-2) and senescent markers, researchers provide evidence that virus-infected lung cells acquire cell senescence properties, which also leading to the expression of proinflammatory cytokines.

Study: Alveolar type II cells harboring SARS-CoV-2 exhibit senescence with proinflammatory phenotype. Image credit: Kateryna Kon / Shutterstock

Coronavirus 2019 (COVID-19) infection is an infection caused by the pathogen SARS-CoV-2. It has led to more deaths among the elderly and those with other diseases. Although the virus mainly affects the respiratory system, the disease can spread to several other organs along with elevated levels of proinflammatory cytokines, also known as cytokine (which can cause cytokine). to be lethal).

Viral disease is associated with DNA damage and cell fusion, known as promoters of cellular senescence. When senescence occurs in cells, cell division and growth can cease, causing unstable cell cycle arrest, altered metabolism, and proinflammatory properties known as Senescence Associated Secretory Phenotype (SASP). Although there is little evidence linking viruses to cellular senescence, viral infection can lead to proinflammatory responses that may induce senescence.

Thus, senescence may be a protective mechanism against viral infection and there may be increased senescence in infected cells and those around them. In a new study published on the bioRxiv * preprint server, researchers report the results of their study on the link between SARS-CoV-2 infection and cellular senescence.

Testing of SARS-CoV-2 infectious lung tissue

For their study, the authors obtained lung samples from 10 COVID-19 patients. They used previously developed monoclonal antibodies to SARS-CoV-2 spike proteins to test for COVID-19 in the lung cells.

The authors detected the virus in type-II alveolar pneumocytes (AT2) of all patients. The infectious AT2 cells were sometimes large and showed a strong, diffuse, or cytoplasmic granular signal in immunohistochemistry staining. The infectious cells covered the alveolar wall and exited the airways, or were present in the alveolar spaces, either alone or in clusters.

An electron microscope confirmed the presence of the virus in the AT2 cells. At high elevation, the authors observed virions near the endoplasmic reticulum, indicating their growth, and in the cytoplasmic bones indicating their admission to the extracellular space.

Using descriptive methods for detecting senescence, the team found that approximately 8 to 17% of SARS-CoV-2 infectious AT2 cells responded to SenTraGor, a marker for senescence. These were also confirmed by another sign of senescence. These cells were sometimes collected and expressed by angiotensin converting enzyme 2 (ACE2), another sign of ACE2-mediated SARS-CoV-2 infection.

In serial sections and co-staining analysis, the authors found proinflammatory cytokines IL-1b and IL-6, which were not found in the non-COVID-19 tumor. This is evidence of the sensation of SASP by senescent cells, the authors wrote.

The expression of these cytokines, key components of cytokine storm, suggests that cell senescence through SASP plays a role in adverse clinical outcomes in some COVID-19 patients. Thus, in COVID-19 patients, senescence alters the characteristics of respiratory cells, causing them to secrete cytokines that are released into the bloodstream.

Representative images of G2 (i), SenTraGor (ii) and ACE-2 (iii) staining in serial segments of COVID-19 lungs. B. Representative results from double staining experiments showing cytoplasmic localization of viral spike proteins in cells that are simultaneously positive with SenTraGor (senescent) (i), and p16INK4A nuclear expression in cells that are simultaneously positive le SenTraGor (ii). B (i) left inner cell expression of AT2 alone exhibits cytoplasmic immunopositivity for the viral Spike protein. C. Representative images of G2 (i), SenTraGor (ii) and ACE-2 (iii) staining in serial sections of non-COVID-19 “normal” lung parenchyma near tumor (n = 10, age on match with cases shown in Fig. 2A). Range of SenTraGor labeling indexes: 1-2%. Morphologically, senescent AT2 cells in non-COVID-19 mice show a reduced size compared to those in COVID-19 cases. D. Graph showing differences in SenTraGor staining between non-COVID19 and COVID19 cases, *** p <0.001 (Mann-Whitney U test). E. Representative images of Interleukin 1ß (IL-1ß) (i), SenTragor (ii) and Interleukin-6 (IL-6) (iii) in serial segments of COVID-19 lungs. F. Representative results from double staining experiments showing cytoplasmic localization of IL-1ß in cells simultaneously positive with SenTraGor (i), and IL-6 expression in cells simultaneously positive with SenTraGor (ii). G. Representative images of IL-1ß (i), SenTraGor (ii) and IL-6 (iii) in serial segments of non-COVID-19 lungs (see also C). Original size: 400x, Insets 630x; Countertain rapid hematoxylin and nuclear (Bi and F); DAB IHC - brown color; In co-staining SenTraGor was visualized by histo-IHC hybrid chromogenic reaction BCIP / NBT (dark blue perinuclear and cytoplasmic blue color).

Representative images of G2 (i), SenTraGor (ii) and ACE-2 (iii) staining in serial segments of COVID-19 lungs. B. Representative results from double staining experiments showing cytoplasmic localization of viral spike proteins in cells that are simultaneously positive with SenTraGor (senescent) (i), and p16INK4A nuclear expression in cells that are simultaneously positive le SenTraGor (ii). B (i) left inner cell expression of AT2 alone exhibits cytoplasmic immunopositivity for the viral Spike protein. C. Representative images of G2 (i), SenTraGor (ii) and ACE-2 (iii) staining in serial sections of non-COVID-19 “normal” lung parenchyma near tumor (n = 10, age on match with cases shown in Fig. 2A). Range of SenTraGor labeling indexes: 1-2%. Morphologically, senescent AT2 cells in non-COVID-19 mice show a reduced size compared to those in COVID-19 cases. D. Graph showing differences in SenTraGor staining between non-COVID19 and COVID19 cases, *** p <0.001 (Mann-Whitney U test). E. Representative images of Interleukin 1ß (IL-1ß) (i), SenTragor (ii) and Interleukin-6 (IL-6) (iii) in serial segments of COVID-19 lungs. F. Representative results from double staining experiments showing cytoplasmic localization of IL-1ß in cells simultaneously positive with SenTraGor (i), and IL-6 expression in cells simultaneously positive with SenTraGor (ii). G. Representative images of IL-1ß (i), SenTraGor (ii) and IL-6 (iii) in serial segments of non-COVID-19 lungs (see also C). Original size: 400x, Insets 630x; Countertain rapid hematoxylin and nuclear (Bi and F); DAB IHC - brown color; In co-staining SenTraGor was observed with BCIP / NBT chromogenic hybrid histo-IHC reaction (perinuclear and cytoplasmic dark blue color).

Cell senescence can cause a cytokine storm

Although the results show cell senescence in SARS-CoV-2 disease, it is not yet known whether senescence already exists before infection, making the cells more susceptible to disease, or whether the disease is causing senescence in response to antiviral.

The authors write that both cases are possible. In elderly patients and people with age-related diseases, senescence is expected to be high, making them vulnerable to a proinflammatory response. In the samples they tested, the authors found that the proportion of senescent cells was higher in patients over 73 years compared to those in younger patients.

The observed senescence may be in response to the viral infection. Infectious senescent cells could produce paracrine senescence in nearby cells. “Regardless of where it comes from, both conditions are related to SASP secretion that is at least partially similar to a source or even a stimulus of the proinflammatory cytokines, commonly seen in the blood of COVID-19 patients , ”Wrote the authors.

Therefore, the findings suggest that further research in the field using senotherapeutics, such as senolytics, SASP modulators or inhibitors, may help in the development of anti-SARS-CoV-2 therapy.

* Important message

bioRxiv publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical practice / behavior, or be treated as information established.

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