Glyceraldehyde-3-Phosphat Dehydrogenase (GAPDH) as a candidate gene in the pathogenesis of parotid gland cystadenolymphoma

Introduction:

Cystadenolymphomas (CALs) represent the second most frequent benign tumors of the parotid gland and are characterized by the presence of onkocytes, embedded in a lymphocyte rich stroma. These onkocytes are found to contain a large number of functionally compromised mitochondria. The underlying pathogenesis of CALs is unknown. In preliminary investigations, we observed a distinct GAPDH expression pattern in tumor onkocytes.

Methods:

Formalin-fixed paraffin embedded (FFPE) CAL and control parotid gland tissues were used for analysis. 3 or 6 µm thick FFPE tissue sections were placed on regular microscope slides or slides, specifically designed for laser microdissection (LMD) (MembraneSlides, Zeiss) and stained with hematoxylin eosin (HE). Immunohistochemistry, using anti GAPDH and normal IgG (control) primary antibodies, was implemented and digital image analysis was performed (ImageJ/Fiji). LMD was carried out with a PALM® MicroBeam microscope (Zeiss). Whole cellular RNA was isolated with the RNeasy FFPE kit (Qiagen) and GAPDH expression was quantified by qPCR.

Results:

CAL onkocytes exhibited a heterogenous patchy GAPDH staining pattern. Digital image analysis revealed a significantly lower (p < 0.005) GAPDH signal in CAL onkocytes compared with parotid gland ductal (control) cells. Similarly, qPCR using RNA derived from cells obtained after LMD showed on average lower GAPDH mRNA transcript levels in onkocytes compared with normal ductal cells that in some measurements reached significance (p = 0.0441).

Conclusions:

It was reported that GAPDH is required for cellular mitophagy. The loss of GAPDH expression in CAL onkocytes could therefore be implicated in the observed accumulation of aged mitochondria and the development of CAL.

Publication History

Publication Date:
18 April 2018 (online)