Effect of age on ultrastructural changes of cortisone treated mouse hepatic cells

Morphological aspects of aging liver: half a century of progress in Japan

The most important morphological aspects of the physiological changes of the liver with age are decreases in the numbers of hepatocytes and their mitochondria, coupled with increases in their volumes. The latter is considered to partially compensate for the decrease in numbers of hepatocytes and mitochondria, but leads to a more limited reserve capacity and thus to a condition in which liver function can be more readily exhausted. The binuclearity and polyploidization of the hepatocytes increase with age and are considered to be due to inhibition of their cell division process. Our studies on the parabiosis between young and old rats and mice, on the implantation of isolated hepatocytes in the spleens of rats of different ages, and on the regenerative process after partial hepatectomy in rats of different ages, suggested the existence of humoral inhibitory factor(s) for the division of the cells and their mitochondria. Morphological studies on the native and Hawaiian Japanese, as well as on the USA Caucasians and the Costa Rican Latinos revealed that a difference in the process of the age-related decrease in hepatocyte number among different ethnicities is mainly due to differences in nutritional conditions rather than to genetic factors. Experimental studies are now being carried out on the effect(s) of various dietary conditions on age-related changes of the liver, and the results obtained support the findings of the geographical studies.

Hepatocyte fine structure during maturation and senescence

Aging is accompanied by a myriad of changes in cell structure, function, and composition. The fact that much of the information concerning age-related alterations in cellular morphology is qualitative precludes meaningful correlations with biochemical changes in order to enhance data interpretation. The mammalian liver has been subjected to both qualitative and quantitative evaluations of hepatocyte structure as a function of aging, i.e., development, maturation, and senescence. Although these data are characterized by considerable variability and, in some instances, blatant contradictions, there exists sufficient agreement in several parameters to permit a consensus in the inbred rat model. Certainly the volume of individual hepatocytes increases with age, and many of the organelle compartments reflect this change. While old rats exhibit a high incidence of polyploidy, there is no definitive evidence to demonstrate a concomitant increase in the binuclear hepatocyte index. Several specific hepatocellular organelles undergo changes in their relative volume or surface area that appear to correlate with functional alterations. The volume density of the lysosomal compartment enlarges significantly during senescence and is accompanied by increased activities of several constituent hydrolases. The hepatic concentration of smooth-surfaced endoplasmic reticulum declines markedly with aging, as does the yield of liver microsomes and the activities of several microsomal enzymes, e.g., mono-oxygenases and glucose-6-phosphatase. However, the responses of the majority of hepatocyte organelles to aging is varied and inconsistent based on the limited data currently available.

An electron microscopic examination of age-related changes in the rat liver. The influence of diet

The influence of age and diet on the ultrastructure of hepatocytes is reported. The following dietary manipulations were investigated: Group 1, fed ad libitum a diet containing 21% protein; Group 2, fed a similar diet but restricted to 60% of the intake of Group 1 from 6 weeks of age onwards; Group 3, restricted from 6 weeks to 6 months of age and thereafter fed ad libitum; Group 4, restriction started at 6 months of age; Group 5, fed ad libitum a diet containing 12.6% protein. In all groups the size of hepatocytes was found not to increase during adult life. The size of hepatocytes in Groups 2 and 4 was the same as or larger than that of the other groups; thus food restriction resulted in a decreased number of hepatocytes. Changes in the structure of some organelles and the accumulation of lipofuscin granules occurred with advancing age and the extent of these age-related changes was less in Groups 2 and 4 than in the other groups. These morphologic findings in conjunction with our previously reported metabolic findings provide a new view of the action of food restriction on the aging process.

Age changes of mitochondria of rat kidney

Age-related changes of the mitochondria in the renal proximal convoluted tubules, using 2-, 12-, 18- and 25-29-month-old rats, were morphometrically examined with reference to the mitochondrial function. Mitochondrial volume per cell was significantly larger in 12- and 18-month-old rats compared with that in 2- and 25-29-month-old animals. The total volume of mitochondria in the proximal convoluted tubules was estimated to be maximal in the 18-month-old rats, and decreased significantly in the 25-29-month-old ones; the mitochondrial cristae were arranged most sparsely in the former case and became significantly compact in the latter. The number of epithelial cells in the 25-29-month-old rats was also significantly smaller than in the 18-month-old rats. From the above, in the 25-29-month-old rats, each mitochondrion seems to function more actively to compensate for the numerical loss of cells and their mitochondria.

Stereological analysis of hepatic fine structure in the Fischer 344 rat. Influence of sublobular location and animal age

Stereological analysis of hepatic fine structure in Fischer 344 male rats at 1, 6, 10, 16, 20, 25, and 30 mo of age revealed differences in the amounts and distributions of hepatocellular organelles as a function of sublobular location or animal age. Between 1 and 16 mo of age, both the centrolobular and periportal hepatocytes increased in volume by 65 and 35%, respectively. Subsequently, the cell volumes declined until the hepatocytes of 30-mo-old rats approached the size of those found in the youngest animals. Regardless of animal age, the centrolobular cells were consistently larger than the corresponding periportal hepatocytes. The cytoplasmic and ground substance compartments reflected similar changes in their volumes, although there was no significant alteration in the nuclear volume. The volumes of the mitochondrial and microbody compartments increased and decreased concomitant with the changes in average hepatocyte size. Both lobular zones in the 30-mo-old rats contained significantly smaller relative volumes of mitochondria than similar parenchyma in 16-mo-old animals. The volume density of the dense bodies (lysosomes) increased markedly in both lobular zones between 1 and 30 mo of age, confirming reports of an age-dependent increase in this organelle. The surface area of the endoplasmic reticulum in the centrolobular and periportal hepatocytes reached its maximum level in the 10-mo-old rats and subsequently declined to amounts which approximated those measured in the 1-mo-old animals. This age-related loss of intracellular membrane is attributable to a significant reduction in the surface area of the smooth-surfaced endoplasmic reticulum (SER) in animals beyond 16 mo of age. The amount of rough-surfaced endoplasmic reticulum (RER) in the periportal parenchymal cells was unaffected by aging, but the centrolobular hepatocytes of 30-mo-old animals contained 90% more RER than similar cells in the youngest rats. The centrolobular parenchyma contained more SER and the portal zones more RER throughout the age span studied. These quantitative data suggest that (a) certain hepatic fine structural parameters undergo marked changes as a function of animal age, (b) there exists a gradient in hepatocellular fine structure across the entire liver lobule, and (c) there are remarkable similarities in hepatocyte ultrastructure between very young and senescent animals, including cell size and the amount of SER.

The formation of enlarged and giant mitochondria in the aging process of human hepatic cells

Measurement of area, circumference and total length of membrane profile of mitochondria of hepatic cells in 61 human biopsy materials (age range 21 to 81 years) have been ultramicrometrically performed on electron micrographs, supplemented by electroncytochemical examination of cytochrome c oxidase activity in some cases. The mitochondria decreased in number after 60 years of age. The first stage of compensation for the numerical loss of mitochondria was achieved by an increase of cristae in each mitochondrion, followed with a five year lag by an increase in their size. Formation of enlarged and giant mitochondria in aging process following the significant decrease in their number, may be considered to be of similar mechanism to polyploidization of the nucleus, whose division is interfered.