Proteasome inhibition by lipofuscin/ceroid during postmitotic aging of fibroblasts.

We have studied the effects of hyperoxia and of cell loading with artificial lipofuscin or ceroid pigment on the postmitotic aging of human lung fibroblast cell cultures. Normobaric hyperoxia (40% oxygen) caused an irreversible senescence-like growth arrest after about 4 wk and shortened postmitotic life span from 1-1/2 years down to 3 months. During the first 8 wk of hyperoxia-induced 'aging', overall protein degradation (breakdown of [(35)S]methionine metabolically radiolabeled cell proteins) increased somewhat, but by 12 wk and thereafter overall proteolysis was significantly depressed. In contrast, protein synthesis rates were unaffected by 12 wk of hyperoxia. Lysosomal cathepsin-specific activity (using the fluorogenic substrate z-FR-MCA) and cytoplasmic proteasome-specific activity (measured with suc-LLVY-MCA) both declined by 80% or more over 12 wk. Hyperoxia also caused a remarkable increase in lipofuscin/ceroid formation and accumulation over 12 wk, as judged by both fluorescence measurements and FACscan methods. To test whether the association between lipofuscin/ceroid accumulation and decreased proteolysis might be causal, we next exposed cells to lipofuscin/ceroid loading under normoxic conditions. Lipofuscin/ceroid-loaded cells indeed exhibited a gradual decrease in overall protein degradation over 4 wk of treatment, whereas protein synthesis was unaffected. Proteasome specific activity decreased by 25% over this period, which is important since proteasome is normally responsible for degrading oxidized cell proteins. In contrast, an apparent increase in lysosomal cathepsin activity was actually caused by a large increase in the number of lysosomes per cell. To test whether lipofuscin/ceroid could in fact directly inhibit proteasome activity, thus causing oxidized proteins to accumulate, we incubated purified proteasome with lipofuscin/ceroid preparations in vitro. We found that proteasome is directly inhibited by lipofuscin/ceroid. Our results indicate that an accumulation of oxidized proteins (and lipids) such as lipofuscin/ceroid may actually cause further increases in damage accumulation during aging by inhibiting the proteasome.

Hermansky-Pudlak syndrome: an immunologic assessment of 15 cases.

PURPOSE: The Hermansky-Pudlak syndrome is an autosomal recessive disorder consisting of the triad of oculocutaneous albinism, a storage pool platelet defect, and multisystem tissue deposition of ceroid pigment. Although the underlying metabolic defect has not been identified, secondary or associated effects on the immune system are suggested by reports of an association with disorders such as pulmonary fibrosis, granulomatous colitis, lupus, and frequent bacterial infections. We evaluated a large group of patients with the Hermansky-Pudlak syndrome to assess immune competence in this condition. PATIENTS AND METHODS: Fifteen patients with this syndrome were studied. Control subjects included healthy volunteers in the same age range as the patients. Peripheral blood lymphocytes and neutrophils were isolated according to previously described methods. Immunofluorescent staining, flow cytometry, and cytotoxicity assays were performed. Determination of lymphocyte transformation, mixed lymphocyte response, and neutrophil function was made. RESULTS: Immunoglobulin levels, complement, lymphocyte subsets, natural killer and lymphokine-activated cytotoxicity, mixed lymphocyte responses, and lectin-induced transformation were normal in all patients. In addition, there was no evidence for a lymphocyte proliferative response to a preparation of urinary ceroid pigment isolated from these patients. Neutrophil function, including luminol-dependent chemiluminescence, chemotaxis, and aggregation was not significantly different from control values. CONCLUSION: The results suggest that there is no generalized defect of peripheral blood lymphocyte or neutrophil function in the Hermansky-Pudlak syndrome. We propose that future studies should examine the possibility that associated disorders arise from a defect within the monocyte-macrophage system, perhaps secondary to ceroid accumulation.