Peroxisomes Are Highly Abundant and Heterogeneous in Human Parotid Glands

Abstract

The parotid gland is one of the major salivary glands producing a serous secretion, and it plays an essential role in the digestive and immune systems. Knowledge of peroxisomes in the human parotid gland is minimal; furthermore, the peroxisomal compartment and its enzyme composition in the different cell types of the human parotid gland have never been subjected to a detailed investigation. Therefore, we performed a comprehensive analysis of peroxisomes in the human parotid gland’s striated duct and acinar cells. We combined biochemical techniques with various light and electron microscopy techniques to determine the localization of parotid secretory proteins and different peroxisomal marker proteins in parotid gland tissue. Moreover, we analyzed the mRNA of numerous gene encoding proteins localized in peroxisomes using real-time quantitative PCR. The results confirm the presence of peroxisomes in all striated duct and acinar cells of the human parotid gland. Immunofluorescence analyses for various peroxisomal proteins showed a higher abundance and more intense staining in striated duct cells compared to acinar cells. Moreover, human parotid glands comprise high quantities of catalase and other antioxidative enzymes in discrete subcellular regions, suggesting their role in protection against oxidative stress. This study provides the first thorough description of parotid peroxisomes in different parotid cell types of healthy human tissue.

The peroxisome: an update on mysteries 3.0

“…The properties of peroxisomes in parotid glands, which are a major type of salivary gland producing serous saliva, have recently been characterised for the first time. They are highly abundant in all parotid gland cells in both mice and humans, though they vary in number and protein content both within and between cells (Watermann et al 2021(Watermann et al , 2023. A greater number of peroxisomes were observed in striatal duct cells compared to acinar cells, as well as stronger immunofluorescence staining of peroxisomal proteins including catalase, thiolase, and PEX14.…”

“…A greater number of peroxisomes were observed in striatal duct cells compared to acinar cells, as well as stronger immunofluorescence staining of peroxisomal proteins including catalase, thiolase, and PEX14. Furthermore, mRNAs encoding peroxisomal proteins required for biogenesis, β-oxidation and plasmalogen synthesis, as well as antioxidant enzymes, were expressed throughout parotid glands, suggesting a role for peroxisomal metabolism and oxidative defence in the function of this tissue (Watermann et al 2021(Watermann et al , 2023. Notably, levels of peroxisomal proteins also varied between neoplastic and healthy parotid tissues, with tumour samples exhibiting both up-and downregulation of peroxins and a general upregulation of proteins involved in lipid transport and β-oxidation, indicating a dysregulation of peroxisome biogenesis and lipid metabolism which may be either a driver or consequence of tumour progression (Meyer et al 2021).…”