Effect of aging and late onset dietary restriction on antioxidant enzymes and proteasome activities, and protein carbonylation of rat skeletal muscle and tendon

Abstract

Many studies have shown that lifelong dietary restriction (DR) can retard aging processes. Very few reports, however, are found that examined the effect of late onset DR on biochemical parameters in aging animals [Goto, S., Takahashi, R., Araki, S., Nakamoto, H., 2002b. Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism. Ann. NY Acad. Sci. 959, 50–56]. We studied the effect of every-other-day feeding, initiated at the age of 26.5 months and continued for 3.5 months, on antioxidant enzymes, protein carbonyls, and proteasomes of the gastrocnemius muscle and tendon in rats. Age-related increase in the activity and content of Cu, Zn-SOD and the content of Mn-SOD was attenuated by the DR in both tissues. The same was true for glutathione peroxidase and catalase activities. Significant increase with age in protein reactive carbonyl derivatives (RCD) in the tendon was noted that was partially reversed by the DR. No significant change of RCD, however, was observed in the skeletal muscle. The age-related and DR-induced changes of the RCD in the tendon appeared to be associated with proteasome activity that decreases with age and increases by the DR. It is suggested that the late onset DR can have beneficial effects on the locomotive functions by reducing age-associated potentially detrimental oxidative protein damage in the tendon.

Introduction

The free radical theory of aging proposes that aging is primarily caused by radicals derived from cellular metabolic processes and/or exogenous sources such as chemicals and irradiations (Harman, 1956, Harman, 1981). Age-associated decline of physiological functions can be the result of significantly increased production of reactive oxygen species (ROS), including highly reactive hydroxy radicals which overwhelm the capability of antioxidant systems and scavenging activities of oxidatively modified molecules. The decline might also be due to decreased efficiency of repair activities that lead to the accumulation of oxidative damage together with the processes mentioned earlier. ROS can modify lipids, proteins and DNA. Accumulation of oxidized proteins appears to occur at a much higher extent (i.e. on the order of 5–10% of total cellular proteins on average, Stadtman, 1992) than that of oxidatively modified lipid (Miyazawa et al., 1993) or DNA (Richter et al., 1988, Kaneko et al., 1996), which is far below 0.1% as a steady state level. Moreover, oxidative modifications of amino acid residues in antioxidant and repair enzymes would curb their biological activities resulting in further accumulation of oxidative damage (Levine et al., 1981, Stadtman, 1992). Therefore, the degree of oxidative modifications of these enzymes is considered to have significant deteriorating consequences on cell function.

It has been reported by several groups of investigators that reactive carbonyl derivatives (RCD) of proteins which are believed to be formed by ROS-induced modification of side chains of arginyl, aspartyl, glutamyl, lysyl, prolyl, and/or threonyl residues accumulate with age (Stadtman, 1992, Goto et al., 2002a). Accumulation of RCD in the brain proteins appears to be closely related to impaired cognitive function with age, suggesting that accumulation of carbonylated proteins is not just a result but likely to be a causative factor of age-associated decline of physiological functions in the brain (Carney et al., 1991, Forster et al., 1996, Butterfield et al., 1997, Radák et al., 2001). It should also be mentioned, however, that the increase in oxidative damage appears to occur in a limited number of species of proteins rather than proteins in general (Goto et al., 1999), and the issue of age-related general changes of protein carbonyl contents is controversial (Goto and Nakamura, 1997).

Aging of mammalian species including human and rat is associated with decline in muscle mass and force generation (Lexell et al., 1983, Holloszy et al., 1991). Force generated in the sarcomere in the muscle is transmitted to bones to result in locomotion in which process the tendon, a connective tissue, plays a curricular role. Age-related changes in the antioxidant system and oxidative damage to proteins of the skeletal muscle have been reported (Ji et al., 1990, Ji, 1993, Leeuwenburgh et al., 1994, Aspnes et al., 1997). The tendon, however, has remained unexplored in this respect.

Dietary restriction (DR) can increase average as well as maximum life span of a variety of mammalian species as well as non-mammalian species such as fish, nematodes and insects, serving as an important tool to study mechanisms of normal and decelerated aging (Yu, 1996, Sohal and Weindruch, 1996). A lifelong DR is known to attenuate age-related increase in the accumulation of oxidative damage in different organs (Sohal et al., 1993, Chen and Yu, 1994, Kaneko et al., 1997, Radák and Goto, 1998). It has been shown that proteins in hepatocytes from dietarily restricted old mice have significantly shorter half-lives than those of their ad libitum fed counterparts (Ishigami and Goto, 1990). These results suggest possible beneficial effects of DR on protein functions that decrease with age. Limited information is available, however, on whether a shorter period of DR initiated late in life has beneficial effects on the oxidative status in proteins. If proved, the late onset DR would provide a biological basis of potential intervention for human aging after middle age (Goto et al., 2002b).

In the present study, we investigated the activity and content of antioxidant enzymes, proteasome activities and RCD in the gastrocnemius muscle and the connected Achilles tendon of young control (10 month-old) and aged rats subjected to either ad libitum feeding or DR initiated at the age of 26.5 months and continued for 3.5 months.