L-Arginine Enhances Oral Keratinocyte Proliferation under High-Glucose Conditions via Upregulation of CYP1A1, SKP2, and SRSF5.

High glucose inhibits oral keratinocyte proliferation. Diabetes can lead to delayed oral wound healing and periodontal disease. L-Arginine, one of the most versatile amino acids, plays an important role in wound healing, organ maturation, and development. In this study, L-Arginine was found to enhance oral keratinocyte proliferation under high-glucose conditions. RNA sequencing analysis discovered a significant number of genes differentially upregulated following L-Arginine treatment under high-glucose conditions. Cytochrome P450 family 1 subfamily A member 1 (CYP1A1) was the most significantly upregulated gene at 24 and 48 h after L-Arginine treatment. Gene Ontology enrichment analysis found that cell proliferation- and mitosis-related biological processes, such as mitotic nuclear division, mRNA processing, and positive regulation of cell cycle processes, were significantly upregulated. Pathway enrichment analysis found that S-phase kinase-associated protein 2 (SKP2) and serine- and arginine-rich splicing factor 5 (SRSF5) were the top upregulated genes in cell cycle and spliceosome pathways, respectively. Indirect immunofluorescent cytochemistry confirmed increased protein levels of CYP1A1, SKP2, and SRSF5 after L-Arginine treatment. Knockdown of CYP1A1, SKP2, and SRSF5 abolished the enhanced proliferative effect of L-Arginine on oral keratinocytes under high-glucose conditions. In conclusion, L-Arginine enhances oral keratinocyte proliferation under high-glucose conditions via upregulation of CYP1A1, SKP2, and SRSF5, suggesting that supplemental L-Arginine in oral care products may be beneficial for oral tissue repair and regeneration.

High Glucose Induces Late Differentiation and Death of Human Oral Keratinocytes.

Keratinocytes are essential cells for wound repair. Impaired oral wound healing is common in diabetic patients with periodontal disease. High glucose, or hyperglycemia, impairs the cellular function of different cell types. However, it is unknown whether high glucose has a detrimental effect on the functions of oral keratinocytes. In the current study, a human gingival keratinocyte cell line, telomerase immortalized gingival keratinocytes (TIGK), was treated with high glucose (24 and 48 mM) for up to 120 h. Proliferation, migration, cell viability, and production of markers of differentiation, growth factors and enzymatic antioxidants were assessed after high glucose treatment. The results showed that high glucose significantly inhibited TIGK proliferation and migration. High glucose also induced significant cell death through apoptosis and necrosis as determined by flow cytometry, especially at 120 h after high glucose treatment. Necrosis was the dominant form of cell death induced. Real-time PCR showed that high glucose treatment upregulated mRNA expression of late keratinocyte differentiation makers, such as keratin 1, 10, 13 and loricrin, and downregulated enzymatic antioxidants, including superoxide dismutase 1, catalase, nuclear factor erythroid 2 -related factor 2, heme oxygenase 1. In conclusion, high glucose impairs the proliferation and migration of oral keratinocytes and likely induces cell death through the promotion of late cell differentiation and down-regulation of enzymatic antioxidants.