Secondary alterations of human hepatocellular peroxisomes

Hypothyroidism Intensifies Both Canonic and the De Novo Pathway of Peroxisomal Biogenesis in Rat Brown Adipocytes in a Time-Dependent Manner

Despite peroxisomes being important partners of mitochondria by carrying out fatty acid oxidation in brown adipocytes, no clear evidence concerning peroxisome origin and way(s) of biogenesis exists. Herein we used methimazole-induced hypothyroidism for 7, 15, and 21 days to study peroxisomal remodeling and origin in rat brown adipocytes. We found that peroxisomes originated via both canonic, and de novo pathways. Each pathway operates in euthyroid control and over the course of hypothyroidism, in a time-dependent manner. Hypothyroidism increased the peroxisomal number by 1.8-, 3.6- and 5.8-fold on days 7, 15, and 21. Peroxisomal presence, their distribution, and their degree of maturation were heterogeneous in brown adipocytes in a Harlequin-like manner, reflecting differences in their origin. The canonic pathway, through numerous dumbbell-like and “pearls on strings” structures, supported by high levels of Pex11β and Drp1, prevailed on day 7. The de novo pathway of peroxisomal biogenesis started on day 15 and became dominant by day 21. The transition of peroxisomal biogenesis from canonic to the de novo pathway was driven by increased levels of Pex19, PMP70, Pex5S, and Pex26 and characterized by numerous tubular structures. Furthermore, specific peroxisomal origin from mitochondria, regardless of thyroid status, indicates their mutual regulation in rat brown adipocytes.

HSD17B4, ACAA1, and PXMP4 in Peroxisome Pathway Are Down-Regulated and Have Clinical Significance in Non-small Cell Lung Cancer

To explore the potential functions and clinical significances of peroxisomes during lung cancer development and progression, we investigated the expressional profiles of peroxisome pathway genes and their correlations with clinical features in non-small cell lung cancer (NSCLC). The RNA-seq data of NSCLC including lung squamous carcinoma (LUSC) and lung adenocarcinoma (LUAD) patients with their clinical information were downloaded from The Cancer Genome Atlas (TCGA). Gene expression comparisons between tumor and normal samples were performed with edgeR package in R software and the results of the 83 peroxisome pathway genes were extracted. Through Venn diagram analysis, 38 common differentially expressed peroxisome pathway genes (C-DEPGs) in NSCLC were identified. Principal components analysis (PCA) was performed and the 38 C-DEPGs could discriminate NSCLC tumors from the non-tumor controls well. Through Kaplan-Meier survival and Cox regression analyses, 11 of the C-DEPGs were shown to have prognostic effects on NSCLC overall survival (OS) and were considered as key C-DEPGs (K-DEPGs). Through Oncomine, Human Protein Atlas (HPA) and the Clinical Proteomic Tumor Analysis Consortium (CPTAC), three K-DEPGs (HSD17B4, ACAA1, and PXMP4) were confirmed to be down-regulated in NSCLC at both mRNA and protein level. Their dy-regulation mechanisms were revealed through their correlations with their copy number variations and methylation status. Their potential functions in NSCLC were explored through their NSCLC-specific co-expression network analysis, their correlations with immune infiltrations, immunomodulator gene expressions, MKI67 expression and their associations with anti-cancer drug sensitivity. Our findings suggested that HSD17B4, ACAA1, and PXMP4 might be new markers for NSCLC diagnosis and prognosis and might provide new clues for NSCLC treatment.

Human peroxisomal disorders

Peroxisomes are single membrane-bound cell organelles performing numerous metabolic functions. The present article aims to give an overview of our current knowledge about inherited peroxisomal disorders in which these organelles are lacking or one or more of their functions are impaired. They are multiorgan disorders and the nervous system is implicated in most. After a summary of the historical names and categories, each having distinct symptoms and prognosis, microscopic pathology is reviewed in detail. Data from the literature are added to experience in the authors' laboratory with 167 liver biopsy and autopsy samples from peroxisomal patients, and with a smaller number of chorion samples for prenatal diagnosis, adrenal-, kidney-, and brain samples. Various light and electron microscopic methods are used including enzyme- and immunocytochemistry, polarizing microscopy, and morphometry. Together with other laboratory investigations and clinical data, this approach continues to contribute to the diagnosis and further characterization of peroxisomal disorders, and the discovery of novel variants. When liver specimens are examined, three main groups including 9 novel variants (33 patients) are distinguished: (1) absence or (2) presence of peroxisomes, and (3) mosaic distribution of cells with and without peroxisomes (10 patients). Renal microcysts, polarizing trilamellar inclusions, and insoluble lipid in macrophages in liver, adrenal cortex, brain, and in interstitial cells of kidney are also valuable for classification. On a genetic basis, complementation of fibroblasts has classified peroxisome biogenesis disorders into 12 complementation groups. Peroxisome biogenesis genes (PEX), knock-out-mice, and induction of redundant genes are briefly reviewed, including some recent results with 4-phenylbutyrate. Finally, regulation of peroxisome expression during development and in cell cultures, and by physiological factors is discussed.

Morphological adaptations of human liver peroxisomes in cholestasis

Part of the bile acid synthesis takes place in peroxisomes. An altered enterohepatic circulation of bile acids might influence peroxisomal beta-oxidation enzymes and peroxisomal morphology. We performed a morphological and morphometric investigation of peroxisomes in liver biopsy samples of eight patients with cholestasis of different origin: graft versus host reaction (n = 1), obstruction of the bile flow (n = 3), and drug-induced cholestatic hepatitis (n = 4). Peroxisomes were identified using catalase cytochemistry. They were regularly shaped and showed individual differences in electron density. A perinuclear distribution was observed in a variable number of hepatocytes in each sample. Morphometric analysis of peroxisomes revealed an increase in numerical density and surface density in all, and a decreased mean diameter in four liver samples. Based on previously obtained data in experimental animals, we hypothesize that the observed alterations in peroxisomal morphology indicate an enhanced metabolic activity of the enzymes in the peroxisomal matrix. Among them are enzymes involved in bile acid synthesis.

Morphometric characteristics of human hepatocellular peroxisomes in alcoholic liver disease

Hepatocellular peroxisomes harbor one of the metabolic pathways for ethanol metabolism (i.e., catalase in the presence of H2O2-generating enzymes). We studied the morphometric characteristics of these organelles in 26 biopsy samples of patients with different alcohol-induced lesions (12 with steatosis, 5 with hepatitis, and 9 with cirrhosis) and compared the findings with those obtained in seven control livers. All 33 human liver biopsy samples were stained for catalase activity to facilitate peroxisomal identification. Morphometric analysis of the peroxisomes was performed on calibrated electron micrographs. The numerical density of the peroxisomes was significantly increased to 183%, whereas the mean peroxisomal diameter (dcircle) revealed a significant decrease to 89%. This resulted in a normal volume density of the peroxisomal compartment, whereas the surface density was significantly induced. Peroxisomal shape was not different between alcoholic and control livers. When alcoholic livers were divided into three subgroups according to histopathological findings, similar morphometric results were obtained when compared with control livers, although significantly was sometimes lost. No differences in peroxisomal characteristics were found among alcoholic subgroups. The mean peroxisomal diameter per human liver (alcoholic and control) was inversely correlated to the numerical density. It is concluded that the peroxisomal adaptation in human alcoholic liver is such as to create an efficient environment for a presumably increased peroxisomal metabolism.