Molecular Mechanisms of SARS-CoV-2 Nonspike Structural Proteins in Pathological Changes of Human Oral Mucosa and Periodontal Ligament

ORCID

Abstract

BackgroundThe oral cavity is increasingly recognised as a biologically relevant site of SARS-CoV-2 infection and tissue involvement. However, the pathological and molecular consequences of SARS-CoV-2 in oral mucosa and periodontal tissues remain insufficiently defined. In particular, the effects of viral structural proteins on epithelial organisation, differentiation and tissue homeostasis are not fully understood.AimsThis study aimed to define the pathological effects of SARS-CoV-2 associated exposure in human oral tissues and to investigate the molecular mechanisms by which viral structural proteins disrupt epithelial and periodontal homeostasis. A further aim was to establish relevant experimental systems for mechanistic investigation of oral COVID-19 pathology.MethodsCOVID-19 patient tissues and complementary experimental models were employed, including an ex vivo mouse tongue culture system, a full-thickness human oral mucosa three-dimensional (3D) equivalent, and periodontal ligament in vitro models. Histological, immunohistochemical, immunofluorescent, transcriptional and proteomic analyses were used to assess epithelial differentiation, tissue architecture, ciliary changes, cell cycle behaviour and fibrotic remodelling following exposure to SARS-CoV-2 structural proteins.ResultsCOVID-19 oral mucosa exhibited reduced Keratin 4 and E-Cadherin expression, with increased expression of Keratin 14, consistent with impaired epithelial differentiation and disrupted tissue integrity. Tissue engineered oral epithelial models reproduced key structural features of native oral mucosa and enabled direct testing of viral protein function. Among the non-spike structural proteins examined, the envelope protein showed the strongest pathogenic effect, disrupting epithelial stratification and organisation in three-dimensional oral mucosa models. Viral protein exposure was further associated with loss of ciliated epithelial cells, reduced ciliary structure, altered cell cycle progression and induction of CNN2, supporting a mechanistic link between ciliary dysfunction, abnormal epithelial remodelling and disturbed homeostasis. In human periodontal ligament fibroblasts and related three-dimensional in vitro models, the dominant pathological response was fibrotic remodelling, characterised by increased Collagen I expression, reduced MMP1, enhanced matrix deposition, and a broader fibrotic degeneration phenotype, particularly in response to envelope and membrane proteins. Proteomic profiling further suggested that suppression of mitochondrial fatty acid β-oxidation may contribute to this pro-fibrotic response.ConclusionsSARS-CoV-2 associated exposure disrupts oral epithelial and periodontal tissue homeostasis. Human oral cavity is therefore a relevant target of COVID-19 associated pathology, and non-spike structural proteins, particularly the envelope protein, appear to contribute directly to epithelial disorganisation, ciliary loss, cell cycle disturbance and periodontal fibrotic remodelling. This study provides experimental platforms and mechanistic insight that advance current understanding of SARS-CoV-2 pathogenesis in oral tissues.

Awarding Institution(s)

University of Plymouth

Supervisor

Bing Hu, Wai Ling Kok, Sally Hanks, Christopher Tredwin

Keywords

SARS-CoV-2, Human oral cavity, Infection, Human oral mucosa

Document Type

Thesis

Publication Date

2026

Embargo Period

2027-09-09

Deposit Date

September 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

This document is currently not available here.

This item is under embargo until 09 September 2027

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