# scRNA-seq reveals persistent aberrant differentiation of nasal epithelium driven by TNFα and TGFβ in post-COVID syndrome

## TL;DR

The study finds that persistent nasal inflammation in post-COVID syndrome is driven by immune signals TNFα and TGFβ, not ongoing viral infection.

## Contribution

The work identifies TNFα and TGFβ as key drivers of epithelial dysfunction in post-COVID syndrome using single-cell RNA sequencing.

## Key findings

- Severe PCS is marked by reduced ciliated cells and increased immune infiltration.
- TNFα and TGFβ drive epithelial-mesenchymal transition and basal cell expansion.
- Chronic cytokine activity, not viral load, underlies sustained nasal epithelium damage.

## Abstract

Post-COVID syndrome (PCS) affects approximately 3-17% of individuals following acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and poses a potential global health burden. While improved assessment strategies are emerging, mechanistic insights and treatment options remain limited. This study investigates molecular mechanisms underlying PCS using single-cell RNA (scRNA) transcriptomics combined with in vitro validation. scRNA analysis is performed on nasal biopsies from 25 patients with moderate or severe PCS to investigate differential cell types, signalling pathways, and cell-cell communication. Air-liquid interface cultures are used to validate findings, focusing on the TNFα-TGFβ axis. Severe PCS shows reduced numbers of ciliated cells, increased immune cell infiltration, and heightened inflammatory signaling that drives TGFβ and TNFα upregulation, in the absence of a detectable viral load. These changes trigger epithelial-mesenchymal transition, basal cell expansion and a mis-stratified nasal epithelium. In vitro experiments confirm TGFβ and TNFα as causal cytokines promoting ciliated cell loss and increased basal cell abundance. These findings indicate a sustained severe PCS is not driven by ongoing viral load but by immune cell activity and chronic cytokine production. Targeting the TNFα-TGFβ axis may mitigate immune-mediated nasal tissue damage and support epithelium restoration, offering a potential therapeutic strategy for PCS.

In this work, authors apply single-cell transcriptomics to nasal biopsies from post-COVID syndrome patients, revealing chronic inflammation driven by TNFα and TGFβ, alongside persistent airway epithelial remodelling in the absence of viral load.