Accelerated ageing: from mechanism to therapy through animal models

Ageing research benefits from the study of accelerated ageing syndromes such as Hutchinson-Gilford progeria syndrome (HGPS), characterized by the early appearance of symptoms normally associated with advanced age. Most HGPS cases are caused by a mutation in the gene LMNA, which leads to the synthesis of a truncated precursor of lamin A known as progerin that lacks the target sequence for the metallopotease FACE-1/ZMPSTE24 and remains constitutively farnesylated. The use of Face-1/Zmpste24-deficient mice allowed us to demonstrate that accumulation of farnesylated prelamin A causes severe abnormalities of the nuclear envelope, hyper-activation of p53 signalling, cellular senescence, stem cell dysfunction and the development of a progeroid phenotype. The reduction of prenylated prelamin A levels in genetically modified mice leads to a complete reversal of the progeroid phenotype, suggesting that inhibition of protein farnesylation could represent a therapeutic option for the treatment of progeria. However, we found that both prelamin A and its truncated form progerin can undergo either farnesylation or geranylgeranylation, revealing the need of targeting both activities for an efficient treatment of HGPS. Using Face-1/Zmpste24-deficient mice as model, we found that a combination of statins and aminobisphosphonates inhibits both types of modifications of prelamin A and progerin, improves the ageing-like symptoms of these mice and extends substantially their longevity, opening a new therapeutic possibility for human progeroid syndromes associated with nuclear-envelope defects. We discuss here the use of this and other animal models to investigate the molecular mechanisms underlying accelerated ageing and to test strategies for its treatment.     

Cytokine-induced activation of mixed lineage kinase 3 requires TRAF2 and TRAF6

Mixed lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that activates multiple mitogen-activated protein kinase (MAPK) pathways in response to growth factors, stresses and the pro-inflammatory cytokine, tumor necrosis factor (TNF). MLK3 is required for optimal activation of stress activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) signaling by TNF, however, the mechanism by which MLK3 is recruited and activated by the TNF receptor remains poorly understood. Here we report that both TNF and interleukin-1β (IL-1β) stimulation rapidly activate MLK3 kinase activity. We observed that TNF stimulates an interaction between MLK3 and TNF receptor associated factor (TRAF) 2 and IL-1β stimulates an interaction between MLK3 and TRAF6. RNA interference (RNAi) of traf2 or traf6 dramatically impairs MLK3 activation by TNF indicating that TRAF2 and TRAF6 are critically required for MLK3 activation. We show that TNF also stimulates ubiquitination of MLK3 and MLK3 can be conjugated with lysine 48 (K48)- and lysine 63 (K63)-linked polyubiquitin chains. Our results suggest that K48-linked ubiquitination directs MLK3 for proteosomal degradation while K63-linked ubiquitination is important for MLK3 kinase activity. These results reveal a novel mechanism for MLK3 activation by the pro-inflammatory cytokines TNF and IL-1β.     

Intervention of cardiomyocyte death based on real-time monitoring of cell adhesion through impedance sensing

Cardiomyocyte death caused by proinflammatory cytokines, such as Tumor necrosis factor α (TNF-α), is one of the hot topics in cardiovascular research. TNF-α can induce multiple cell processes that are dependent on the treatment time although the long-term treatment definitely leads to cell death. The ability to intervene in cell death will be invaluable to reveal the effects of short-term TNF-α treatment to cardiomyocytes. However, a real-time monitoring technique is needed to guide the intervention of cell responses. In this work, we employed the impedance-sensing technique to real-time monitor the equivalent cell–substrate distance of cardiomyocytes via electrochemical impedance spectroscopy (EIS) and electrical cell–substrate impedance sensing (ECIS). In the stabilized cardiomyocyte culture, the sustained TNF-α treatment caused strengthened cell adhesion in the first 2 h which was followed by the transition to cell detachment afterwards. Considering cell detachment was an early morphological evidence of cell death, we removed TNF-α from the cardiomyocyte culture before the transition to achieve the intervention of cell responses. The result of this intervention showed that cell adhesion was continuously strengthened before and after the removal of TNF-α, indicating the short-term treated cardiomyocytes did not undergo death processes. It was also demonstrated in TUNEL and TBE tests that the percentages of apoptosis and cell death were both lowered.     

Sqd interacts with the Drosophila retinoblastoma tumor suppressor Rbf

The retinoblastoma tumor suppressor (RB) serves as a scaffold to coordinate binding of numerous proteins, including E2F and histone deacetylases, through its C-terminal domain. The amino-terminal half of RB has few known binding partners and its function is not well understood. We used the amino-terminal domain of the Drosophila retinoblastoma tumor suppressor Rbf (RbfN) to identify novel binding partners by immunoprecipitation coupled with mass spectrometry. Our experiment revealed that the RNA-binding protein Squid (Sqd) is a putative interacting partner of RbfN. Western blot confirmed that Sqd interacts with the amino-terminal domain of Rbf. We observed that Sqd colocalizes with RbfN in Drosophila salivary gland cells. We also show that double RNAi knockdown of Rbf and Sqd in the eye results in an extensive loss of eye bristles, suggesting that Rbf and Sqd function in a common pathway. We conclude from our studies that Rbf physically and genetically interacts with Sqd. We propose that the retinoblastoma tumor suppressor may play a novel role in RNA processing through interaction with RNA-binding proteins.     

Identification of a common microdeletion cluster in 7q21.3 subband among patients with myeloid leukemia and myelodysplastic syndrome

Monosomy 7 and interstitial deletions in the long arm of chromosome 7 (−7/7q−) is a common nonrandom chromosomal abnormality found frequently in myeloid disorders including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and juvenile myelomonocytic leukemia (JMML). Using a short probe-based microarray comparative genomic hybridization (mCGH) technology, we identified a common microdeletion cluster in 7q21.3 subband, which is adjacent to ‘hot deletion region’ thus far identified by conventional methods. This common microdeletion cluster contains three poorly characterized genes; Samd9, Samd9L, and a putative gene LOC253012, which we named Miki. Gene copy number assessment of three genes by real-time PCR revealed heterozygous deletion of these three genes in adult patients with AML and MDS at high frequency, in addition to JMML patients. Miki locates to mitotic spindles and centrosomes and downregulation of Miki by RNA interference induced abnormalities in mitosis and nuclear morphology, similar to myelodysplasia. In addition, a recent report indicated Samd9 as a tumor suppressor. These findings indicate the usefulness of the short probe-based CGH to detect microdeletions. The three genes located to 7q21.3 would be candidates for myeloid tumor-suppressor genes on 7q.     

MMSET is overexpressed in cancers: Link with tumor aggressiveness

MMSET is expressed ubiquitously in early development and its deletion is associated with the malformation syndrome called Wolf-Hirschhorn syndrome. It is involved in the t(4; 14) (p16; q32) chromosomal translocation, which is the second most common translocation in multiple myeloma (MM) and is associated with the worst prognosis. MMSET expression has been shown to promote cellular adhesion, clonogenic growth and tumorigenicity in multiple myeloma. MMSET expression has been recently shown to increase with ascending tumor proliferation activity in glioblastoma multiforme. These data demonstrate that MMSET could be implicated in tumor emergence and/or progression. Therefore, we compared the expression of MMSET in 40 human tumor types - brain, epithelial, lymphoid - to that of their normal tissue counterparts using publicly available gene expression data, including the Oncomine Cancer Microarray database. We found significant overexpression of MMSET in 15 cancers compared to their normal counterparts. Furthermore MMSET is associated with tumor aggressiveness or prognosis in many types of these aforementioned cancers.Taken together, these data suggest that MMSET potentially acts as a pathogenic agent in many cancers. The identification of the targets of MMSET and their role in cell growth and survival will be key to understand how MMSET is associated with tumor development.     

Enhancement of Th1 immune response by CD8α dendritic cells loaded with heat shock proteins enriched tumor extract in tumor-bearing mice

The discovery of dendritic cells (DCs) as professional antigen presenting cells has opened up new possibilities for their use in the development of tumor vaccines. We investigated the effect of the CD8α⁺ DCs loaded with heat-treated tumor lysate (HTL) as a vaccine in tumor immunotherapy. The HTL loaded CD8α⁺ DCs, TL loaded CD8α⁺ DCs and unloaded CD8α⁺ DCs were subcutaneously injected in the fibrosarcoma-bearing mice. The splenocyte proliferation and the shifting of Th1/Th2 response were measured. The results indicated a significant increase in the lymphocytes proliferation and the IFN-γ production in the test group of mouse splenocytes. According to the results, HTL loaded CD8α⁺ DCs vaccine significantly decreased tumor growth and longer survival than the other immunized animals. These findings show that anti-tumor immune response against the fibrosarcoma can be induced by HTL loaded CD8α⁺ DCs and may provide a useful therapeutic model for development of approaches to tumor treatments.