Effect of age and dietary restriction on expression of heat shock protein 70 in rat alveolar macrophages

Dietary restriction (DR) is the only effective experimental manipulation known to retard aging ill rodents, and this manipulation has been shown to alter a variety of processes that change with age. However, there is no information on the effect of DR on macrophage function. In the present study, the effect of aging and DR on the ability of alveolar macrophages (AMs) to express the heat shock gene, hsp70 was studied. AMs were isolated by lavage from the lungs of young (4 - 6 months) and old (24 - 26 months) rats fed either ad libitum (AL) or a restricted diet (60% of AL). There was no age-related change in the number of cells recovered from young and old rats fed AL. However, the number of cells recovered from the lungs of the DR rats was reduced, and this decrease was statistically significant in young rats. The expression of heat shock protein 70 (hsp70) was measured by the level of the hsp70 mRNA transcript in total RNA isolated from AMs cultured under two conditions: in suspension and after adherence to plastic. When AMs were incubated at 37°C in suspension, no detectable hsp70 expression was observed; however, hsp70 expression was induced at 37°C when the AMs adhered to the plastic culture dishes. Hsp70 mRNA levels were rapidly induced by heat shock (43°C, 1 h) in AMs cultured both in suspension and on plastic. The induction of hsp70 expression did not change significantly with either age or DR in AMs cultured in suspension. In contrast, the induction of hsp70 mRNA levels by AMs adherent to plastic culture plates decreased approximately 70% with age, and hsp70 induction was greater in AMs isolated from DR rats; this difference was statistically significant in young rats. The induction of hsp70 by heat shock (43°C, 1 h) also decreased with age in the adherent AMs, and DR increased the induction of hsp70 expression three- to fourfold in adherent AMs from both young and old rats.