In humans, the composition of gut commensal bacteria is closely correlated with obesity. The bacteria modulate metabolites and influence host immunity. In this study, we attempted to determine whether there is a direct correlation between specific commensal bacteria and host metabolism. As mice aged, we found significantly reduced body weight and fat mass in Atg7 mice when compared with Atg7 mice. When mice shared commensal bacteria by co-housing or feces transfer experiments, body weight and fat mass were similar in both mouse groups. By pyrosequencing analysis, Bacteroides acidifaciens (BA) was significantly increased in feces of Atg7 mice compared with those of control Atg7 mice. Wild-type C57BL/6 (B6) mice fed with BA were significantly more likely to gain less weight and fat mass than mice fed with PBS. Of note, the expression level of peroxisome proliferator-activated receptor alpha (PPARα) was consistently increased in the adipose tissues of Atg7 mice, B6 mice transferred with fecal microbiota of Atg7 mice, and BA-fed B6 mice. Furthermore, B6 mice fed with BA showed elevated insulin levels in serum, accompanied by increased serum glucagon-like peptide-1 and decreased intestinal dipeptidyl peptidase-4. These finding suggest that BA may have potential for treatment of metabolic diseases such as diabetes and obesity.

Morphological change is one of the cardinal features of the senescent phenotype; for example, senescent human diploid cells have a flat large shape. However, the mechanisms underlying such senescence-related morphological alterations have not been well studied. To investigate this situation, we characterized the senescence-dependent changes of cellular structural determinants in terms of their levels and activities. These determinants included integrins, focal adhesion complexes, and small Rho GTPases, and special emphasis was placed on their relationships with caveolin-1 status. We observed that the expression integrin ␤ 1 and focal adhesion kinase (FAK) were increased and that the phosphorylations of FAK and paxillin, hallmarks of focal adhesion formation, were also increased in senescent human diploid fibroblast cells. Moreover, the Rho GTPases Rac1 and Cdc42 were found to be highly activated in senescent cells. In addition, focal adhesion complexes and Rho GTPases were up-regulated in the caveolin-rich membrane domain in the senescent cells. Activated Rac1 and Cdc42 directly interacted with caveolin-1 in senescent cells. Interestingly, caveolin-1 knock-out senescent cells, achieved by using small interfering RNA and antisense oligonucleotide, showed disrupted focal adhesion formation and actin stress fibers via the inactivation of FAK, which resulted in morphological adjustment to the young cell-like small spindle shape. Based on the results obtained, we propose that caveolin-1 plays an important role in senescence-associated morphological changes by regulating focal adhesion kinase activity and actin stress fiber formation in the senescent cells.

Hyporesponsiveness to growth factors is one of the fundamental characteristics of senescent cells. We previously reported that the up-regulation of caveolin attenuates the growth factor response and the subsequent downstream signal cascades in senescent human diploid fibroblasts. Therefore, in the present experiment, we investigated the modulation of caveolin status in senescent cells to determine the effect of caveolin on mitogenic signaling efficiency and cell cycling. We reduced the level of caveolin-1 in senescent human diploid fibroblasts using its antisense oligonucleotides and small interfering RNA, and this resulted in the restoration of normal growth factor responses such as the increased phosphorylation of Erk, the nuclear translocation of pErk, and the subsequent activation of p-Elk upon epidermal growth factor stimulation. Moreover, DNA synthesis and the re-entry of senescent cells into cell cycle were resumed upon epidermal growth factor stimulation concomitantly with decreases in p53 and p21. Taken together, we conclude that the loss of mitogenic signaling in senescent cells is strongly related to their elevated levels of caveolin-1 and that the functional recovery of senescent cells at least in the terms of growth factor responsiveness and cell cycle entry might be achieved simply by lowering the caveolin level.Caveolae are vesicular organelles that represent a subdivision of the plasma membrane (1, 2). They are most abundant in terminally differentiated cell types, i.e. adipocytes, endothelial cells, and muscle cells. Moreover, it has been suggested that caveolae may function as subcellular compartments for the storage of inactive signaling molecules to regulate activation and to facilitate cross-talk between distinct signaling cascades (3, 4).Caveolin, a 21-24-kDa integral membrane protein, is the principal component of caveolae, and the caveolin gene family consists of caveolin-1, -2, and -3. Caveolin-1 and -2 are coexpressed, form a hetero-oligomer in the plasma membrane, and exist in many cell types (5-7), whereas the expression of caveolin-3 is muscle-specific (8). Moreover, recent studies have suggested a regulatory role for caveolin in addition to its structural function. For example, the stable expressions of the caveolin-1 or -3 genes in caveolin-deficient mammalian cells induced the formation of caveolae structures (9).The caveolin functions as scaffolding protein within the caveolae membrane and interacts with signaling proteins such as EGFR, 1 G-proteins, Src-like kinases, Ha-Ras, protein kinase C, endothelial nitric-oxide synthase, and integrin (10 -15). In addition, a short cytosolic N-terminal region of caveolin is involved in the formation of oligomers and mediates the interaction with signaling molecules, which result in the their inactivation (4). The targeted down-regulation of caveolin-1 is sufficient to drive cell transformation and hyperactivates the Erk kinase cascade (16). And caveolin levels in most tumor tissues are significantly lower than in normal tissues, suggesting ...

Major vault protein (MVP), the main component of vault complex, is overexpressed in many multidrug-resistant cancer cell lines, suggesting a possible role for MVP in cell signaling and survival. In this study, we have found that MVP is markedly increased in senescent human diploid fibroblasts (HDFs) as well as in aged organs. We examined whether MVP expression might be affected by apoptotic stress in an aging-dependent manner. We treated young and senescent HDFs with apoptosis-inducing agents such as H 2 O 2 , staurosporine and thapsigargin, and monitored MVP expression. We found that MVP expression is markedly reduced in young HDFs but not in senescent HDFs, in response to apoptotic stresses. Downregulation of MVP increased the sensitivity of senescent HDFs to apoptosis. Also, the level of antiapoptotic B-cell lymphoma protein-2 (Bcl-2) was significantly reduced and the accumulation of c-Jun increased in MVP knocked-down senescent HDFs. Moreover, treatment of MVP knocked-down senescent HDFs with SP600125, a specific c-Jun NH (2) Vaults are large ribonucleoprotein particles found in a great portion of eukaryotic cells. The vault particle is a multimeric structure composed of three proteins -the major vault protein (MVP), two minor vault proteins, vault poly (ADP-ribose) polymerase (VPARP) and telomerase-associated protein-1 (TP-1), and four small untranslated vault RNAs (vRNAs). 1 MVP is the main component of the vault complex accounting for 75% of the total particle mass. 2 The vault particle has been so named because it has a barrel-shaped structure, reminiscent of the vaulted ceilings in cathedrals. 3 The interaction of MVP by its coiled coil domain is involved in the formation of the basic vault complex. 4 MVP expression is upregulated in cancers such as melanoma, 5 colon cancer 6 and gliomas 7 during acquisition of multidrug resistance 8,9 and during differentiation of dendritic cells. 10 MVP expression has also been shown to be induced by histone deacetylase inhibitors such as sodium butyrate, 11 phorbol 12-myristate 13-acetate (PMA) and cytarabine 12 as well as by cytotoxic drugs. 12-14 MVP/vaults have been proposed to be important in intracellular transport, 15-17 innate immunity 18 and virus infection. 19 Several studies demonstrated that MVP is important in cell signaling [20][21][22] and in cell survival. 10,20,23 For example, serumdeprived MVP-deficient mouse embryonic fibroblasts (MEFs) exhibit significantly increased cell death when compared with wild-type MEFs. 20 Therefore, the role of MVP as a scaffolding protein for signaling proteins, especially for cell survival, has received more attention than as a transport vehicle. However, the exact role of MVP in cell survival is not well understood. In this study, we found that apoptotic resistance of senescent human diploid fibroblasts (HDFs) correlates with the increased content of MVP in the senescent cells. This is the first report implicating MVP in apoptosis resistance of senescent HDFs. ResultsIncreased expression of MVP in aged cells and organs...

We previously reported that senescent human diploid fibroblasts (HDFs) are resistant to apoptosis induced by H 2 O 2 and staurosporine. We report here that senescent HDFs are resistant to thapsigargin-induced apoptosis as well. These agonists caused the reductions in mitochondrial membrane potential (MMP) and in the apoptosis inhibitory protein (B-cell lymphoma) only in young HDFs but not in senescent HDFs. In addition, downregulation of Bcl-2 increased the sensitivity of senescent HDFs to apoptosis induction, suggesting the significant role of Bcl-2 in apoptosis resistance of the senescent HDFs. We further found that P-cAMP response element-binding protein (CREB), a positive regulator of Bcl-2, decreased in stress-induced apoptosis of young HDFs but not in senescent HDFs, and that Bcl-2 was markedly reduced in CREB small interfering RNA (siRNA), transfected senescent HDFs. In addition, activity of protein phosphatase 2A (PP2A), which dephosphorylates p-CREB, significantly increased in young HDFs but not in senescent HDFs treated with H 2 O 2 , staurosporine or thapsigargin. Taken together, these results suggest that failure of stress-induced downregulation of Bcl-2 underlies resistance of senescent HDFs to apoptosis.