Increased resistance of lipofuscin-loaded prematurely senescent fibroblasts to starvation-induced programmed cell death

Abstract

Alterations of cellular structures often found in ageing cells is mainly the result of production of reactive oxygen species and a consequence of aerobic life. Both oxidative stress and decreased degradative capacity of lysosomal system cause accumulation of intralysosomal age-related pigment called lipofuscin. To investigate the influence of lipofuscin on cell function, we compared survival of lipofuscin-loaded and control human fibroblasts following complete starvation induced by exposure to phosphate-buffered saline (PBS). Starving of control fibroblasts resulted in lysosomal alkalinisation, relocation of cathepsin D to the cytosol, caspase-3 activation and, finally, cell death, which became evident 72 h after the start of exposure to PBS. Increase of lysosomal pH was significantly less prominent in lipofuscin-loaded cells than in controls and was accompanied neither by leakage of cathepsin D nor by caspase-3 activation even 96 h after the initiation of starvation. Suppression of autophagy by 3-methyladenine (3-MA) accelerated cell death, while inhibition of cathepsin D delayed it, implying an important role of autophagy in cell survival during starvation and showing the involvement of lysosomes in starvation-induced cell death. Disturbed apoptotic response found in lipofuscin-loaded cells can be interpreted as an example of hormesis--an adaptation to low doses of otherwise harmful agents, in this case of lipofuscin, which has a protective effect at moderate amounts but becomes toxic at large quantities.

Lysosome-targeted stress reveals increased stability of lipofuscin-containing lysosomes

“…The current study is a continuation of the recently presented work of our group, showing that lipofuscinloaded cells are more resistant to cell death (Stroikin et al 2007). Here, instead of studying the apoptotic response, we focus on the effects of lipofuscin on Fig.…”

“…In opposition, some researchers doubt that a convincing evidence of deleterious effects of lipofuscin has ever been demonstrated . Moreover, we recently showed that moderate levels of lipofuscin have protective effects on cell survival during nutritional deprivation (Stroikin et al 2007). The previously suggested idea, that lipofuscin permanently occupies active sites of lysosomal enzymes, preventing their translocation to the cytosol and engagement in programmed cell death during lysosomal stress, is consistent with the present findings of decreased cytosolic translocation of cathepsin D in lipofuscin-loaded cells.…”

“…Thus, it has been suggested that newly produced lysosomal enzymes are misplaced to the lipofuscin-loaded lysosomes in a futile attempt to degrade lipofuscin instead of performing a useful function within autophagolysosomes (Terman and Brunk 2004). On the other hand, we recently found that moderate levels of lipofuscin are protective and increase the resistance of ageing fibroblasts to cell death (Stroikin et al 2007). Beneficial effect of lipofuscin in this case is explained in terms of hormesis-an adaptation to low doses of otherwise harmful agents (Rattan 2004).…”

“…Such a destabilization was suppressed in lipofuscin-loaded fibroblasts (Stroikin et al 2007). The presented study is a continuation of the previous one in order to further investigate the possible hormetic effect of lipofuscin on lysosomal function.…”

Growing cells at 40% ambient oxygen conditions them to subsequent oxidative stress

“…Recently, however, a paper (Stroikin et al 2007) was published in Biogerontology that attributed to lipofuscin a new and stabilizing effect on lysosomes of starved fibroblasts. In that study it was concluded that lipofuscin in moderate amounts renders cells more, not less, resistant to starvation.…”