Dysregulation of Caveolin-1 Phosphorylation and Nuclear Translocation Is Associated with Senescence Onset

Abstract

We recently reported that the inability of osteoarthritic (OA) chondrocytes to repair oxidative stress (OS) induced DNA damage is linked to Cav-1 overexpression/improper localization. We speculated that the senescent status of OA cells was responsible for this Cav-1 dysregulation. Here, to further investigate this hypothesis, we used Wharton Jelly derived mesenchymal stem cells (WJ-MSCs) and investigated Cav-1 function as cells reached replicative senescence or upon stress induced senescence (SIPS). We showed that Cav-1 is upregulated, phosphorylated and translocated to the nucleus in young WJ-MSCs upon acute exogenous OS, and that it returns back to basal/nonphosphorylated levels and exports the nucleus in the recovery phase. However, as cells reach senescence, this regulation is lost. OS did not induce any Cav-1-mediated response, which is concomitant with the inability of older cells to restore DNA damage. Furthermore, downregulation of Cav-1 resulted in persistent OS-induced DNA damage and subsequent onset of senescence. We also report that the establishment of senescence is mediated by autophagy stimulation, since downregulation of autophagy key molecule Atg5, simultaneously with Cav-1 downregulation, was found to inhibit SIPS. Basically, we propose that Cav-1 involvement in DNA damage response can lead to senescence, either because the damage is extensive or because Cav-1 is absent/unable to perform its homeostatic role.

The establishment of mitotic errors-driven senescence depends on autophagy

“…1 B). The latter, together with our previous observation that late passage WJ-MSCs have higher ROS levels [ 8 ], implies that the intracellular oxidative stress that increases with time could be responsible for DNA damage as well as several other, characteristic of senescent cells, features. For instance, besides double strand breaks other forms of genomic instability, such as micronuclei, giant nuclei, donut shaped nuclei (named here mitotic defects), also increased in late passage cells or when early passage cells were exposed to oxidative insult ( Fig.…”

“…Moreover, the observed here BubR1 decrease in late passage cells, together with its previously reported reduced levels in old mice [ 23 , 24 ], triggered the question about the mechanism responsible for its expression regulation during senescence/aging. As mentioned earlier, it has been suggested that the degradation of proteins shifts from the proteasome to autophagy during senescence [ 30 ], while our lab has also shown that autophagy is dysregulated upon onset of senescence [ 8 , 34 ]. In attempt to shed light in possible connections, we aimed at analyzing protein levels of key molecules of autophagic pathway in early, middle and late passage cells.…”

“…We have previously shown that WJ-MSCs acquire senescence associated beta-galactosidase activity (SA-β-gal) as they reach passage >40 [ 8 ]. Here, we aimed at further characterise late passage cells by comparing them with early (p < 14) and middle (14 < p < 40) passage cells.…”

“…3 A) while Bub1b/BubR1 demonstrated a different pattern; it increased its protein and mRNA levels in middle passage cells while its levels reduced dramatically in late passage cells ( Fig. 3 A and B) or in cells that reach senescence prematurely (Stress Induced Premature Senescence-SIPS) by exposing them to H 2 O 2 and cultivating them for additional passages, a procedure that we have previously described [ 8 ]. The senescence status of these cells was confirmed by the increase in p16 and p21 protein levels ( Fig.…”

“…Oxidative stress has emerged as a crucial factor regulating mesenchymal stem cells’ properties, such as differentiation potential and immunomodulation [ 7 ], while also being a main factor driving their senescence. Elevated levels of reactive oxygen species (ROS) have been detected, by our group [ 8 ] and others [ 9 ], in late passage MSCs as compared to their early passage counterparts, causing macromolecular damage and senescence onset. Even more, even though some controversies have been related to the role of senescence in organismal aging, based mainly in the modest increase in their numbers with time [ 10 ], senescence is implicated in age-related diseases promotion, through the restriction of the regenerative pool of the tissue stem cells [ 11 ].…”