Autophagy in acute liver damage produced in the rat by dimethylnitrosamine

The secretome obtained under hypoxic preconditioning from human adipose-derived stem cells exerts promoted anti-apoptotic potentials through upregulated autophagic process

BACKGROUND

Hypoxic preconditioning (HP) is a stem cell preconditioning modality designed to augment the therapeutic effects of mesenchymal stem cells (MSCs). Although autophagy is expected to play a role in HP, very little is known regarding the relationship between HP and autophagy.

METHODS AND RESULTS

The adipose-derived stem cell (ASC)-secretome obtained under normoxia (NCM) and ASC-secretome obtained under HP (HCM) were obtained by culturing ASCs for 24 h under normoxic (21% partial pressure of O₂) and hypoxic (1% partial pressure of O₂) conditions, respectively. Subsequently, to determine the in vivo effects of HCM, each secretome was injected into 70% partially hepatectomized mice, and liver specimens were obtained. HCM significantly reduced the apoptosis of thioacetamide-treated AML12 hepatocytes and promoted the autophagic processes of the cells (P < 0.05). Autophagy blockage by either bafilomycin A1 or ATG5 siRNA significantly abrogated the anti-apoptotic effect of HCM (P < 0.05), demonstrating that HCM exerts its anti-apoptotic effect by promoting autophagy. The effect of HCM - reduction of cell apoptosis and promotion of autophagic process - was also demonstrated in a mouse model.

CONCLUSIONS

HP appears to induce ASCs to release a secretome with enhanced anti-apoptotic effects by promoting the autophagic process of ASCs.

Cell Autophagy in NASH and NASH-Related Hepatocellular Carcinoma

Autophagy, a cellular self-digestion process, involves the degradation of targeted cell components such as damaged organelles, unfolded proteins, and intracellular pathogens by lysosomes. It is a major quality control system of the cell and plays an important role in cell differentiation, survival, development, and homeostasis. Alterations in the cell autophagic machinery have been implicated in several disease conditions, including neurodegeneration, autoimmunity, cancer, infection, inflammatory diseases, and aging. In non-alcoholic fatty liver disease, including its inflammatory form, non-alcoholic steatohepatitis (NASH), a decrease in cell autophagic activity, has been implicated in the initial development and progression of steatosis to NASH and hepatocellular carcinoma (HCC). We present an overview of autophagy as it occurs in mammalian cells with an insight into the emerging understanding of the role of autophagy in NASH and NASH-related HCC.

Diverse Functions of Autophagy in Liver Physiology and Liver Diseases

Autophagy is a catabolic process by which eukaryotic cells eliminate cytosolic materials through vacuole-mediated sequestration and subsequent delivery to lysosomes for degradation, thus maintaining cellular homeostasis and the integrity of organelles. Autophagy has emerged as playing a critical role in the regulation of liver physiology and the balancing of liver metabolism. Conversely, numerous recent studies have indicated that autophagy may disease-dependently participate in the pathogenesis of liver diseases, such as liver hepatitis, steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma. This review summarizes the current knowledge on the functions of autophagy in hepatic metabolism and the contribution of autophagy to the pathophysiology of liver-related diseases. Moreover, the impacts of autophagy modulation on the amelioration of the development and progression of liver diseases are also discussed.

Autophagic cell death

In this chapter we discuss methods to study autophagic cell death. A large body of evidence demonstrates that autophagy is a cell survival mechanism in response to starvation. The role of autophagy in cell death, however, has long been controversial. Recently, molecular approaches have provided direct evidence that autophagy contributes to cell death in certain contexts. We begin this chapter by outlining methods to quantify cell death, for example by assaying for cell viability. Next, we discuss methods to measure processes involved in cell death, such as caspase activation and autophagy. Finally, we discuss methods to genetically or chemically perturb autophagy to test whether autophagy is required for cell death. Together, these approaches provide a guide to investigate the relationship between autophagy and cell death.

Exercise myopathy: selectively enhanced proteolytic capacity in rat skeletal muscle after prolonged running

The proteolytic capacity of rat skeletal muscle was analyzed during the repair of fiber injuries after strenuous exercise. A single bout of prolonged exercise (8 hr running at a speed of 17 m X min-1) caused a slight fiber necrosis and a selective response in the proteolytic activity of rat skeletal muscle. Acid proteolytic capacity (cathepsin D and acid autolysis) was considerably increased on the 4th day after exertion and partially decreased by the 10th day. The acid hydrolytic response was more prominent in red than in white skeletal muscle. Alkaline proteolytic capacity (alkaline and myofibrillar proteases), increased in several atrophic myopathies, was not affected in exercise myopathy. The rate of neutral autolysis slightly increased after exertion. The protein content of skeletal muscle was decreased on the 4th day after exertion. We suggest that the proteolytic responses to acute injuries, as well as to chronic atrophies, are highly selective in skeletal muscle fibers.

Mechanism of inhibition of hepatic protein synthesis in rats by the carcinogen, methylazoxymethanol acetate

Treatment of rats with the carcinogen, methylazoxymethanol acetate, results in a rapid, marked inhibition of hepatic protein synthesis and disaggregation of polysomes. Studies were undertaken to learn the mechanism by which this carcinogen induces these effects in rat liver. The data show that the inhibition of endogenous protein synthesis is not due to an effect on the high speed supernatant 'factors' but rather at the level of the polysome, and that both free and membrane-bound polysomes are affected. Poly(U)-directed polyphenylalanine synthesis by native ribosomal subunits is greater in preparations isolated from rats treated with carcinogen than it is in controls. Moreover, the native ribosomal subunit fraction from treated livers in response to added rabbit globin mRNA is able to synthesize a protein similar in molecular weight to globin. These studies show that methylazoxymethanol acetate does not induce significant alterations of ribosomal subunits or of initiation factors and suggest that the inhibition of protein synthesis and disaggregation of polysomes may be the results of an alteration of cytoplasmic mRNA, or its association with ribosomes.

Role of the vacuolar apparatus in augmented protein degradation in cultured fibroblasts

Rat embryo fibroblasts, grown in Eagle's MEM with 10% serum, showed a rapid increase in autophagic vacuoles when placed in MEM with 0-1% serum. Concurrent with this response, degradation of cellular proteins showed a 2-fold increase. We did not find any increases in cathepsin D, beta-glucuronidase, beta-galactosidase, and beta-glucosidase, or proteolytic activity of cell homogenates at pH 3.7 towards endogenous substrates. Homogenates prepared in 250 mM sucrose at pH 7.0 showed a 40% increase in protein breakdown. These data support the hypothesis that the induced increase in proteolysis, characteristic of cells placed in a nutritionally deficient medium, is effected by an activated vacuolar apparatus (lysosomes and autophagic vacuoles). We suggest, however, that this mechanism is distinct from normal protein turnover in the cell, but can be rapidly induced by appropriate alterations in the cellular environment. Finally, this induced proteolytic mechanism is not dependent upon an increase in lysosomal enzymes, but rather a structural alteration within the cell which effects a transfer of cellular proteins into the vacuolar apparatus.

Studies on the effects of orally administered Di-(2-ethylhexyl) phthalate in the ferret

A target-organ study of the effects of the phthalate ester di-(2-ethylhexyl) phthalate (DEHP) has been conducted in mature male albino ferrets. DEHP treatment caused a loss of body weight when administered as a 1% (w/w) diet for 14 months. Additionally marked liver enlargement with associated morphological and biochemical changes was observed. These changes consisted of liver cell enlargement, lysosomal changes, dilatation of the endoplasmic reticulum and the depression of a number of marker enzyme activities. The only other tissue observed to be affected by DEHP treatment was the testes where histological evidence of tissue damage was observed in some animals. Studies on the metabolism of [14C]DEHP in the ferret indicated that the diester was metabolised to derivatives of mono-(2-ethylhexyl) phthalate which were excreted in the urine both unconjugated and as glucuronides. The results obtained have been compared with previous studies in the rat and it is concluded that DEHP is hepatotoxic in both species.

Attachment of ribosomes to endoplasmic membranes in mouse pancreas. Degranulation in vivo caused by the inducers of autophagocytosis neutral red, vinblastine, puromycin, and cadmium ions, and prevention by cycloheximide

The present investigation was undertaken to discover whether in vivo inducers of autophagocytosis such as neutral red (0.40 mg/g body weight), cadmium chloride (0.15 mg/animal), vinblastine sulfate (7.5 mg/kg b.w.), and puromycin dihydrochloride (0.20 mg/g b.w.) are able to produce degranulation of rough surfaced endoplasmic reticulum (ER) of pancreatic acinar cells as we suggested earlier. Using a modified method of Blobel and Potter about 30% of the total ribosomes of untreated control pancreas were recovered in the free form, and 70% in the membrane-bound form. Cycloheximide (0.20 mg/g body weight) had no effect on this distribution of ribosomes, while neutral red, cadmium ions, vinblastine, and puromycin led to the presence of more free ribosomes: thus up to 70% of the total cytoplasmic ribosomes were recovered in the free form 30 to 60 min after treatments with the autophagic inducers. Pretreatments with cycloheximide prevented this shift and the distribution of ribosomes remained normal. On the basis of these and previous results we conclude that in pancreas an initial degranulation of the ER caused by these agents is a precondition of membrane transformation in autophagocytosis which is preventable by cycloheximide. Confirming the ultrastructural data of Longnecker et al. on rat pancreas, puromycin was shown to cause different forms of cellular injury including autophagocytosis. All forms of cellular injury were also prevented by pretreatment with cycloheximide in mouse pancreas.

Reversibility of lysosomal and glucose 6-phosphatase changes produced in the rat liver by dimethylnitrosamine

The present investigation was undertaken to discover whether repeated doses of dimethylnitrosamine (DMNA) could produce a cumulative toxic effect on the rat liver. For this purpose doses were selected at a level just too low to produce cytopathological changes, as indicated by depression of glucose-6-phosphatase and induction of autophagic vacuoles (AV) in hepatocytes, when given once only. Single subcutaneous injections of 10 or 3 mg/kg induced these cytopathological changes in the centrilobular (CLB) hepatic cells but when the dose was reduced to 1 mg/kg no such changes were seen. After daily administration of 1 mg/kg for 4 or 8 weeks we observed both glucose-6-phosphatase depression and autophagy, and in addition there was marked hypertrophy of the rough endoplasmic reticulum, nucleolar microsegregation and the appearance of distorted, often ring-shaped mitochondria with shortened cristae. Kupffer cells exhibited a marked increase in lysosomal activity. With the exception of mitochondrial changes and Kupffer cell activity this same picture was observed, although in milder form, when the dose administered was 0.3 or 0.1 mg/kg daily for the same period. When treatment was continued for 12 weeks, however, the only differences from control rats were the presence of hypertrophied rough endoplasmic reticulum (RER) at all three dose levels, nucleolar microsegregation at the upper two dose levels, and pronounced Kupffer cell activity at the top dose. These findings indicate that cumulative cytopathologic effects occur only up to 8 weeks at the dose levels studied but hypertrophy of RER and increased Kupffer cell activity persist up to 12 weeks.