DNA is vulnerable to damage resulting from endogenous metabolites, environmental and dietary carcinogens, some anti-inflammatory drugs, and genotoxic cancer therapeutics. Cells respond to DNA damage ...by activating complex signalling networks that decide cell fate, promoting not only DNA repair and survival but also cell death. The decision between cell survival and death following DNA damage rests on factors that are involved in DNA damage recognition, and DNA repair and damage tolerance, as well as on factors involved in the activation of apoptosis, necrosis, autophagy and senescence. The pathways that dictate cell fate are entwined and have key roles in cancer initiation and progression. Furthermore, they determine the outcome of cancer therapy with genotoxic drugs. Understanding the molecular basis of these pathways is important not only for gaining insight into carcinogenesis, but also in promoting successful cancer therapy. In this Review, we describe key decision-making nodes in the complex interplay between cell survival and death following DNA damage.
The optimal management of a torn anterior cruciate ligament (ACL) of the knee is unknown.
We conducted a randomized, controlled trial involving 121 young, active adults with acute ACL injury in which ...we compared two strategies: structured rehabilitation plus early ACL reconstruction and structured rehabilitation with the option of later ACL reconstruction if needed. The primary outcome was the change from baseline to 2 years in the average score on four subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS)--pain, symptoms, function in sports and recreation, and knee-related quality of life (KOOS(4); range of scores, 0 worst to 100 best). Secondary outcomes included results on all five KOOS subscales, the Medical Outcomes Study 36-Item Short-Form Health Survey, and the score on the Tegner Activity Scale.
Of 62 subjects assigned to rehabilitation plus early ACL reconstruction, 1 did not undergo surgery. Of 59 assigned to rehabilitation plus optional delayed ACL reconstruction, 23 underwent delayed ACL reconstruction; the other 36 underwent rehabilitation alone. The absolute change in the mean KOOS(4) score from baseline to 2 years was 39.2 points for those assigned to rehabilitation plus early ACL reconstruction and 39.4 for those assigned to rehabilitation plus optional delayed reconstruction (absolute between-group difference, 0.2 points; 95% confidence interval, -6.5 to 6.8; P=0.96 after adjustment for the baseline score). There were no significant differences between the two treatment groups with respect to secondary outcomes. Adverse events were common in both groups. The results were similar when the data were analyzed according to the treatment actually received.
In young, active adults with acute ACL tears, a strategy of rehabilitation plus early ACL reconstruction was not superior to a strategy of rehabilitation plus optional delayed ACL reconstruction. The latter strategy substantially reduced the frequency of surgical reconstructions. (Funded by the Swedish Research Council and the Medical Faculty of Lund University and others; Current Controlled Trials number, ISRCTN84752559.)
Apoptosis, autophagy, necrosis and cellular senescence are key responses of cells that were exposed to genotoxicants. The types of DNA damage triggering these responses and their interrelationship ...are largely unknown. Here we studied these responses in glioma cells treated with the methylating agent temozolomide (TMZ), which is a first-line chemotherapeutic for this malignancy. We show that upon TMZ treatment cells undergo autophagy, senescence and apoptosis in a specific time-dependent manner. Necrosis was only marginally induced. All these effects were completely abrogated in isogenic glioma cells expressing O(6)-methylguanine-DNA methyltransferase (MGMT), indicating that a single type of DNA lesion, O(6)-methylguanine (O(6)MeG), is able to trigger all these responses. Studies with mismatch repair mutants and MSH6, Rad51 and ATM knockdowns revealed that autophagy induced by O(6)MeG requires mismatch repair and ATM, and is counteracted by homologous recombination. We further show that autophagy, which precedes apoptosis, is a survival mechanism as its inhibition greatly ameliorated the level of apoptosis following TMZ at therapeutically relevant doses (<100 µM). Cellular senescence increases with post-exposure time and, similar to autophagy, precedes apoptosis. If autophagy was abrogated, TMZ-induced senescence was reduced. Therefore, we propose that autophagy triggered by O(6)MeG adducts is a survival mechanism that stimulates cells to undergo senescence rather than apoptosis. Overall, the data revealed that a specific DNA adduct, O(6)MeG, has the capability of triggering autophagy, senescence and apoptosis and that the decision between survival and death is determined by the balance of players involved. The data also suggests that inhibition of autophagy may ameliorate the therapeutic outcome of TMZ-based cancer therapy.
Genomic prediction of future phenotypes or genetic merit using dense SNP genotypes can be used for prediction of disease risk, forensics, and genomic selection of livestock and domesticated plant ...species. The reliability of genomic predictions is their squared correlation with the true genetic merit and indicates the proportion of the genetic variance that is explained. As reliability relies heavily on the number of phenotypes, combining data sets from multiple populations may be attractive as a way to increase reliabilities, particularly when phenotypes are scarce. However, this strategy may also decrease reliabilities if the marker effects are very different between the populations. The effect of combining multiple populations on the reliability of genomic predictions was assessed for two simulated cattle populations, A and B, that had diverged for T = 6, 30, or 300 generations. The training set comprised phenotypes of 1000 individuals from population A and 0, 300, 600, or 1000 individuals from population B, while marker density and trait heritability were varied. Adding individuals from population B to the training set increased the reliability in population A by up to 0.12 when the marker density was high and T = 6, whereas it decreased the reliability in population A by up to 0.07 when the marker density was low and T = 300. Without individuals from population B in the training set, the reliability in population B was up to 0.77 lower than in population A, especially for large T. Adding individuals from population B to the training set increased the reliability in population B to close to the same level as in population A when the marker density was sufficiently high for the marker-QTL linkage disequilibrium to persist across populations. Our results suggest that the most accurate genomic predictions are achieved when phenotypes from all populations are combined in one training set, while for more diverged populations a higher marker density is required.
Genomic selection uses total breeding values for juvenile animals, predicted from a large number of estimated marker haplotype effects across the whole genome. In this study the accuracy of ...predicting breeding values is compared for four different models including a large number of markers, at different marker densities for traits with heritabilities of 50 and 10%. The models estimated the effect of (1) each single-marker allele single-nucleotide polymorphism (SNP)1, (2) haplotypes constructed from two adjacent marker alleles (SNP2), and (3) haplotypes constructed from 2 or 10 markers, including the covariance between haplotypes by combining linkage disequilibrium and linkage analysis (HAP_IBD2 and HAP_IBD10). Between 119 and 2343 polymorphic SNPs were simulated on a 3-M genome. For the trait with a heritability of 10%, the differences between models were small and none of them yielded the highest accuracies across all marker densities. For the trait with a heritability of 50%, the HAP_IBD10 model yielded the highest accuracies of estimated total breeding values for juvenile and phenotyped animals at all marker densities. It was concluded that genomic selection is considerably more accurate than traditional selection, especially for a low-heritability trait.
Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are age-related neurodegenerative disorders with shared genetic etiologies and overlapping clinical and pathological features. ...Here we studied a novel ALS/FTD family and identified the P362L mutation in the low-complexity domain (LCD) of T cell-restricted intracellular antigen-1 (TIA1). Subsequent genetic association analyses showed an increased burden of TIA1 LCD mutations in ALS patients compared to controls (p = 8.7 × 10−6). Postmortem neuropathology of five TIA1 mutations carriers showed a consistent pathological signature with numerous round, hyaline, TAR DNA-binding protein 43 (TDP-43)-positive inclusions. TIA1 mutations significantly increased the propensity of TIA1 protein to undergo phase transition. In live cells, TIA1 mutations delayed stress granule (SG) disassembly and promoted the accumulation of non-dynamic SGs that harbored TDP-43. Moreover, TDP-43 in SGs became less mobile and insoluble. The identification of TIA1 mutations in ALS/FTD reinforces the importance of RNA metabolism and SG dynamics in ALS/FTD pathogenesis.
•Mutations affecting the low-complexity domain of TIA1 cause ALS and ALS-FTD•ALS-linked TIA1 mutations share a neuropathological TDP-43 signature•TIA1 mutations promote phase separation and impair stress granule dynamics•TDP-43 recruited to poorly dynamic stress granules becomes immobile and insoluble
Mackenzie et al. report the identification of mutations in TIA1 as a novel cause of ALS and ALS-FTD. ALS-linked mutations perturb phase transitions of TIA1, which impair the dynamics of stress granules and indirectly promote TDP-43 insolubility.
TDP-43, an RNA-binding protein that is primarily nuclear and important in splicing and RNA metabolism, is mislocalized from the nucleus to the cytoplasm of neural cells in amyotrophic lateral ...sclerosis (ALS), and contributes to disease. We sought to investigate whether TDP-43 is mislocalized in infections with the acute neuronal GDVII strain and the persistent demyelinating DA strain of Theiler's virus murine encephalomyelitis virus (TMEV), a member of the Cardiovirus genus of Picornaviridae because: i) L protein of both strains is known to disrupt nucleocytoplasmic transport, including transport of polypyrimidine tract binding protein, an RNA-binding protein, ii) motor neurons and oligodendrocytes are targeted in both TMEV infection and ALS. TDP-43 phosphorylation, cleavage, and cytoplasmic mislocalization to an aggresome were observed in wild type TMEV-infected cultured cells, with predicted splicing abnormalities. In contrast, cells infected with DA and GDVII strains that have L deletion had rare TDP-43 mislocalization and no aggresome formation. TDP-43 mislocalization was also present in neural cells of TMEV acutely-infected mice. Of note, TDP-43 was mislocalized six weeks after DA infection to the cytoplasm of oligodendrocytes and other glial cells in demyelinating lesions of spinal white matter. A recent study showed that TDP-43 knock down in oligodendrocytes in mice led to demyelination and death of this neural cell 1, suggesting that TMEV infection mislocalization of TDP-43 and other RNA-binding proteins is predicted to disrupt key cellular processes and contribute to the pathogenesis of TMEV-induced diseases. Drugs that inhibit nuclear export may have a role in antiviral therapy.
O
6-methylguanine-DNA methyltransferase (MGMT) plays a crucial role in the defense against alkylating agents that generate, among other lesions, O
6-alkylguanine in DNA (collectively termed O
...6-alkylating agents O
6AA). The defense is highly important, since O
6AA are common environmental carcinogens, are formed endogenously during normal cellular metabolism and possibly inflammation, and are being used in cancer therapy. O
6AA induced DNA damage is subject to repair, which is executed by MGMT, AlkB homologous proteins (ABH) and base excision repair (BER). Although this review focuses on MGMT, the mechanism of repair by ABH and BER will also be discussed. Experimental systems, in which MGMT has been modulated, revealed that O
6-methylguanine (O
6MeG) and O
6-chloroethylguanine are major mutagenic, carcinogenic, recombinogenic, clastogenic and killing lesions. O
6MeG-induced clastogenicity and cell death require MutSα-dependent mismatch repair (MMR), whereas O
6-chloroethylguanine-induced killing occurs independently of MMR. Extensive DNA replication is required for O
6MeG to provoke cytotoxicity. In MGMT depleted cells, O
6MeG induces apoptosis almost exclusively, barely any necrosis, which is presumably due to the remarkable ability of secondarily formed DNA double-strand breaks (DSBs) to trigger apoptosis via ATM/ATR, Chk1, Chk2, p53 and p73. Depending on the cellular background, O
6MeG activates both the death receptor and the mitochondrial apoptotic pathway. The inter-individual expression of MGMT in human lymphocytes is highly variable. Given the key role of MGMT in cellular defense, determination of MGMT activity could be useful for assessing a patient's drug sensitivity. MGMT is expressed at highly variable amounts in human tumors. In gliomas, a correlation was found between MGMT activity, MGMT promoter methylation and response to O
6AA. Although the human MGMT gene is inducible by glucocorticoids and genotoxins such as radiation and alkylating agents, the role of this induction in the protection against carcinogens and the development of chemotherapeutic alkylating drug resistance are still unclear. Modulation of MGMT expression in tumors and normal tissue is currently being investigated as a possible strategy for improving cancer therapy.
Expansion of a hexanucleotide repeat (HRE), GGGGCC, in the C9ORF72 gene is recognized as the most common cause of familial amyotrophic lateral sclerosis (FALS), frontotemporal dementia (FTD) and ...ALS-FTD, as well as 5–10% of sporadic ALS. Despite the location of the HRE in the non-coding region (with respect to the main C9ORF72 gene product), dipeptide repeat proteins (DPRs) that are thought to be toxic are translated from the HRE in all three reading frames from both the sense and antisense transcript. Here, we identified a CUG that has a good Kozak consensus sequence as the translation initiation codon. Mutation of this CTG significantly suppressed polyglycine-alanine (GA) translation. GA was translated when the G4C2 construct was placed as the second cistron in a bicistronic construct. CRISPR/Cas9-induced knockout of a non-canonical translation initiation factor, eIF2A, impaired GA translation. Transfection of G4C2 constructs induced an integrated stress response (ISR), while triggering the ISR led to a continuation of translation of GA with a decline in conventional cap-dependent translation. These in vitro observations were confirmed in chick embryo neural cells. The findings suggest that DPRs translated from an HRE in C9ORF72 aggregate and lead to an ISR that then leads to continuing DPR production and aggregation, thereby creating a continuing pathogenic cycle.
•Poly-GA translation from the G4C2 expanded repeat starts at CUG located at -24 nucleotide upstream of G4C2 repeats.•Poly-GA translation involves internal ribosome entry.•Poly-GA translation partly depends on eIF2A.•The integrated stress response (ISR) maintains polyGA translation but decreases conventional translation, while polyGA translation triggers the ISR.
Abstract Approximately 20% of familial amyotrophic lateral sclerosis (FALS) cases are caused by mutant superoxide dismutase type 1 (mtSOD1). Although the mechanisms of mtSOD1-induced toxicity remain ...poorly understood, evidence suggests that accumulation of misfolded SOD1 is fundamental to its toxicity and the death of motor neurons. Misfolded mtSOD1 can accumulate inside the endoplasmic reticulum (ER), leading to ER stress, with activation of the unfolded protein response (UPR). We have previously carried out genetic studies focused on PERK (which is an eIF2α kinase that is rapidly activated in response to ER stress and leads to a repression in translation) and GADD34 (which participates in the dephosphorylation of eIF2α). We reported that mtSOD1 transgenic mice that are haploinsufficient for PERK have a significantly accelerated ALS disease, while mtSOD1 mice that are mutated for GADD34 have a remarkably ameliorated disease. Guanabenz, a centrally acting oral drug approved for the treatment of hypertension, enhances the PERK pathway by selectively inhibiting GADD34-mediated dephosphorylation of eIF2α. We have now treated G93A mtSOD1 transgenic mice with guanabenz and found a significant amelioration of disease with a delay in the onset and prolongation of the early phase of disease and survival. Guanabenz-treated G93A mice have less accumulation of mtSOD1 and an enhanced phosphorylation of eIF2α at endstage. This study further emphasizes the importance of the PERK pathway in the pathogenesis of FALS and as a therapeutic target in ALS, and identifies guanabenz as a candidate drug for the treatment of ALS patients.
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