Lipid Metabolism Impairment in Human Gliomas: Expression of Peroxisomal Proteins in Human Gliomas at Different Grades of Malignancy

Abstract

Gliomas are histologically graded by cellularity, cytological atypia, necrosis, mitotic figures, and vascular proliferation, features associated with biologically aggressive behaviour. However, abundant evidence suggests the presence of unrecognized, clinically relevant subclasses of the diffuse gliomas, both in respect to their underlying molecular phenotype and their clinical response to therapy. It is wellknown that patient prognosis and therapeutic decisions rely on accurate pathological grading. Recently, it was reported that human gliomas accumulate lipid droplets during progression, suggesting a lipid metabolism impairment. Considering the crucial role of peroxisomes in lipid metabolism, in the present work we studied the expression profiles of proteins either exclusively localized to peroxisomes, such as peroxin14 (PEX14), peroxisomal membrane protein 70Kda (PMP70), acyl-CoA oxidase, thiolase, or partially associated to peroxisomes such as Hydroxymethylglutaryl-CoA reductase (HMGCoA-red) and peroxisomal-related proteins, namely PPARa, in human glioma specimens at different grades of malignancy. Moreover, Nile red staining of lipid droplets, thin layer chromatography (TLC) and proton nuclear magnetic resonance spectroscopy (NMR) were carried out in order to correlate the biochemical results with the lipid content of tumor tissues. The results obtained indicate that correlating the malignancy grade with the expression of peroxisomal genes and proteins, may constitute a sensitive tool to highlight possible subtypes not recognized by the classical histological techniques.

Hypoxia induces peroxisome proliferator-activated receptor α (PPARα) and lipid metabolism peroxisomal enzymes in human glioblastoma cells

“…The same picture appears for nestin and SDNSF, where the higher expression is observed in glioblastoma cultures with the normal astrocytes completely negative. Since we have previously demonstrated an up-regulation of peroxisomes and peroxisomal related proteins as function of malignancy grade in human glioma (Benedetti et al, 2010), the cultures were then characterized for the presence of peroxisomes by the immunolocalization of the peroxisomal membrane proteins PMP70 and for the presence of lipid droplets (Fig. 2).…”

“…The mechanisms linking cellular replication to lipid metabolism have been under study by several groups. Some Authors have focused on the role of protein prenylation (Jackson et al, 1990), others on the PPARs, which are transcriptional factors that regulate the expression of several enzymes involved in lipid metabolism (Feige et al, 2006;Benedetti et al, 2010).…”

“…In environments with competing metabolic needs, the physiological needs of the cellular environment dictate the state of the peroxisome population and peroxisomal protein content (Keller et al, 1993(Keller et al, , 2000. In our previous study we have demonstrated that peroxisomal number and peroxisomal enzymes, mainly those related to lipid metabolism, are strongly upregulated in function of the glioma malignancy grade (Benedetti et al, 2010), in this study we evaluated the expression profiles of several peroxisomal proteins on primary cultures derived from patients affected by glioma at different grades of malignancy. The results obtained confirmed the upregulation of peroxisomes and peroxisomal proteins as function of the malignancy grade.…”

“…Band relative densities were determined using TotalLab software (ABEL Science-Ware srl, Italy) and values were given as relative units (RU). Immunoblot data were normalized to total protein load by quantification of all samples in a single assay before loading, and confirmation of equal loading by image analysis and scanned Coomassie blue-stained gels after blotting (Benedetti et al, 2010).…”

“…The mechanisms linking cellular replication to lipid metabolism are being studied by several groups. Some authors have focused on the role of protein prenylation, others on the peroxisome proliferator-activated receptors (PPARs), which are transcriptional factors that regulate the expression of several enzymes involved in lipid metabolism (Lemberger et al, 1996;Van den Heuvel, 1999;Benedetti et al, 2010). Peroxisomes, like mitochondria, consume molecular oxygen and metabolize fatty acids, leaving two carbon atoms per cycle to generate acetyl-CoA in a process called b-oxidation.…”