Quantitative immunocytochemical studies on differential induction of serine

Abstract

Differential induction of serine: pyruvate amino-transferase (SPT) in rat liver parenchymal cells by administration of glucagon or di-(2-ethylhexyl)phthalate (DEHP) was studied using post-embedding immunocytochemical techniques and morphometric methods. Two groups of rats were fasted for 5 days and daily received peritoneal injection of glucagon (300 micrograms/100 g) or physiological saline. Another two groups of rats were fed on laboratory chow with or without 2% DEHP for 2 weeks. Livers were perfusion-fixed, cut into tissue sections (50-100 micron), and processed to cytochemistry for catalase, immunocytochemistry for SPT, and conventional procedures for electron microscopy. The morphometric analysis showed that glucagon injection has negligible effect on the volume and numerical density and mean diameter of peroxisomes, whereas volume density of mitochondria was decreased by 25%. By DEHP administration peroxisomes were about 3-fold increased in the volume and numerical density. Mitochondria was increased about 40% in the numerical density, but unchanged in the volume density. Light and electron microscopic immunocytochemistry demonstrated that glucagon injection exclusively enhanced mitochondrial SPT, whereas DEHP administration exclusively induced in peroxisomal SPT. Quantitative analysis showed that by the glucagon injection, the labeling density of mitochondria was increased about 4-fold, but that of peroxisomes was 1.6 times as much as control, while by DEHP administration, the labeling density of peroxisomes was enhanced about 3-fold but that of mitochondria was decreased by 13%. The results clearly indicate that glucagon induces mitochondrial SPT, whereas peroxisome proliferator, DEHP induces peroxisomal SPT.

Pexophagy: The Selective Degradation of Peroxisomes

“…These observations of peroxisome induction and removal have resulted in utilization of yeasts as model organisms to study peroxisome biogenesis, and turnover, which have led to the identification of several genes and mechanisms controlling peroxisome homeostasis [11, 33–47]. In rodents, the administration of phthalate esters or hypolipidemic drugs such as fibrates results in upregulation of peroxisomal proteins and a concomitant increase in peroxisome number [48]. This process is dependent on members of a special class of nuclear receptors, called “peroxisome proliferator-activated receptors (PPARs)” [49, 50].…”

Biochemistry of Peroxisomes

“…AGT in marmoset (147) and rat and mouse liver (139,(148)(149)(150)(151) is present both in peroxisomes and in mitochondria. The peroxisomal and mitochondrial forms have identical physicochemical and enzymological characteristics and are immunologically indistinguishable (139,152).…”

“…Indeed, recent molecular genetic studies (152) have shown that the two forms are products of a single gene with the mRNAs being transcribed from different initiation sites (see section ASSEMBLY OF PEROXISOMES) . In rats, the peroxisomal enzyme is induced by feeding with clofibrate (139) or plasticizer (149), whereas the mitochondrial form is induced by glucagon (139, 148-151, 153, 154).…”

Assays to Monitor Pexophagy in Yeast

“…This can be achieved through the coordination of peroxisome biogenesis and degradation. In rodents, the abundance of peroxisomes increases when the animals are administered with hypolipidemic drugs that are known peroxisome proliferators (Fahimi et al, 1982) or some other chemicals, such as phthalate esters (Yokota, 1986). The number of peroxisomes decreases rapidly and almost returns to the preproliferation state within a week if the drugs are discontinued (Yokota, 1993).…”