Effects of expression level of DNA repair-related genes involved in the NHEJ pathway on radiation-induced cognitive impairment

TDP-43 was Involved in Radiation-induced Neuronal Damage and May Not Through the BDNF/TrkB Pathway

Cognitive dysfunction is the most common form of radiation-induced brain injury. TDP-43 is known to be associated with hippocampal degeneration and cognitive dysfunction, in this study we wanted to know if it also had an effect on radiation-induced hippocampus damage. At first, we found the expression of TDP-43 and p-TDP-43 was increased in the hippocampus of rats with radiation-induced cognitive dysfunction. Single-cell RNA-seq analysis of the rat hippocampus showed that TDP-43 was expressed in all cell types and was significantly upregulated in neuron cells after irradiation. Enrichment analysis of gene ontology (GO) functions and KEGG pathways showed that the differential expression genes in neuron after irradiation may be involved in synaptic plasticity. In vitro, the expression of TDP-43 was also increased in neuron cells after irradiation, while the expression of brain-derived neurotrophic factor (BDNF), TrkB, typical synaptic signature proteins (SYN, GAP43 and PSD95), β-tubulin and dendritic spines were decreased. In the irradiated neurons, the β-tubulin, dendritic and spines typical synaptic signature proteins had more severe damage in pcDNA3.1-TDP-43 plasmid transfections group, however, the damages were alleviated in the siRNA-TDP-43 plasmid transfections group. BDNF was highly expressed in the irradiated pcDNA3.1-TDP-43 plasmid transfections group, while its expression was decreased in the siRNA-TDP-43 group. The TrkB expression was significantly reduced in neurons after exposure to ionizing radiation, however, there was no significant correlation with TDP-43 expression. These data indicate that TDP-43 is involved in radiation-induced neuronal synaptic plasticity decline and developmental damage, furthermore, the BDNF/TrkB signaling pathway may not be involved in this process.

Cranial irradiation induces cognitive decline associated with altered dendritic spine morphology in the young rat hippocampus

OBJECTIVE

Therapeutic irradiation is commonly used to treat brain cancers but can induce cognitive dysfunction, especially in children. The mechanism is unknown but likely involves alterations in dendritic spine number and structure.

METHODS

To explore the impact of radiation exposure on the alteration of dendritic spine morphology in the hippocampus of young brains, 21-day-old Sprague-Dawley rats received cranial irradiation (10 Gy), and changes in spine density and morphology in dentate gyrus (DG) granules and CA1 pyramidal neurons were detected 1 and 3 months later by using Golgi staining. Moreover, we analyzed synapse-associated proteins within dendritic spines after irradiation.

RESULT

Our data showed that cognitive deficits were detected in young rats at both time points postirradiation, accompanied by morphological changes in dendritic spines. Our results revealed significant reductions in spine density in the DG at both 1 month (40.58%) and 3 months (28.92%) postirradiation. However, there was a decrease in spine density only at 1 month (33.29%) postirradiation in the basal dendrites of CA1 neurons and no significant changes in the apical dendrites of CA1 neurons at either time point. Notably, among our findings were the significant dynamic changes in spine morphology that persisted 3 months following cranial irradiation. Meanwhile, we found that depletion of the synapse-associated proteins PSD95 and Drebrin coincided with alterations in dendritic spines.

CONCLUSION

These data suggest that the decreased levels of PSD95 and Drebrin after ionizing radiation may cause changes in synaptic plasticity by affecting the morphological structure of dendritic spines, blocking the functional connectivity pathways of the brain and leading to cognitive impairment. Although the mechanism involved is unclear, understanding how ionizing radiation affects young brain hippocampal tissue may be useful to gain new mechanistic insights into radiation-induced cognitive dysfunction.

Decoding competitive endogenous RNA regulatory network in postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a common postoperative neurological complication in elderly patients. Circular RNAs (circRNAs) are abundant in the mammalian brain and can probably regulate cognitive function. However, the competitive endogenous RNA (ceRNA) regulatory network in POCD remains illiterate. Transcriptomic signatures in the hippocampus of POCD mice derived from the Gene Expression Omnibus (GEO) dataset GSE190880, GSE95070, and GSE115440 were used to identify the circRNA, miRNA, and mRNA expression profiles of POCD mice compared with controls, respectively. A set of differentially expressed RNAs, including 119 circRNAs, 33 miRNAs, and 49 mRNAs were identified. Transcript validation showed the enhanced expression of circ_0001634, circ_0001345, and circ_0001493. A ceRNA regulatory network composed of three circRNAs, three miRNAs, and six mRNAs was established. The hub mRNAs in the ceRNA network were further found to be involved in the hormone catabolic process and regulation of canonical Wnt signaling pathway, revealing their crucial role in POCD. Finally, three miRNAs and four mRNAs were verified by qRT-PCR. These results based on bioinformatics and PCR array suggest that circ_0001634/miR-490-5p/Rbm47, circ_0001634/miR-490-5p/Sostdc1, circ_0001634/miR-7001-5p/Sostdc1, circ_0001345/miR-7001-5p/Sostdc1, and circ_0001493/miR-7001-5p/Sostdc1 may be novel diagnostic biomarkers and therapeutic targets for POCD.

Inhibition of the CDK5/caspase-3 Pathway by p5-TAT Protects Hippocampal Neurogenesis and Alleviates Radiation-induced Cognitive Dysfunction

Radiation-induced cognitive dysfunction is a common complication associated with cranial radiation therapy. Inhibition of hippocampal neurogenesis and proliferation plays a critical role in this complication. Relieving hippocampal apoptosis may significantly protect hippocampal neurogenesis and proliferation. Previous studies have demonstrated that hyperactivity of cyclin-dependent kinase 5 (Cdk5) is closely related to apoptosis. The exact molecular changes and function of Cdk5 in radiation-induced cognitive dysfunction are still not clear. Whether inhibition of Cdk5 and the relevant caspase-3 could improve hippocampal neurogenesis and ameliorate radiation-induced cognitive dysfunction needs further exploration. We hypothesized that inhibition of the Cdk5/caspase-3 pathway by p5-TAT could protect hippocampal neurogenesis and alleviate radiation-induced cognitive dysfunction. In our study, we reported that radiation induced hyperactivity of Cdk5 accompanied by elevation of the levels of cleaved caspase-3, a marker of neuronal apoptosis. Inhibition of hippocampal neurogenesis and proliferation as well as cognitive dysfunction was also observed. p5-TAT, a specific inhibitor of Cdk5, decreased the overactivation of Cdk5 without affecting the levels of Cdk5 activators. Additionally, this treatment suppressed the expression of cleaved caspase-3. We further demonstrated that p5-TAT treatment reduced hippocampal dysfunction and improved behavioral performance. Therefore, Cdk5 inhibition by the small peptide p5-TAT is a promising therapeutic strategy for radiation-induced cognitive dysfunction.

Assessment of Nuclear and Mitochondrial DNA, Expression of Mitochondria-Related Genes in Different Brain Regions in Rats after Whole-Body X-ray Irradiation

Studies of molecular changes occurred in various brain regions after whole-body irradiation showed a significant increase in terms of the importance in gaining insight into how to slow down or prevent the development of long-term side effects such as carcinogenesis, cognitive impairment and other pathologies. We have analyzed nDNA damage and repair, changes in mitochondrial DNA (mtDNA) copy number and in the level of mtDNA heteroplasmy, and also examined changes in the expression of genes involved in the regulation of mitochondrial biogenesis and dynamics in three areas of the rat brain (hippocampus, cortex and cerebellum) after whole-body X-ray irradiation. Long amplicon quantitative polymerase chain reaction (LA-QPCR) was used to detect nDNA and mtDNA damage. The level of mtDNA heteroplasmy was estimated using Surveyor nuclease technology. The mtDNA copy numbers and expression levels of a number of genes were determined by real-time PCR. The results showed that the repair of nDNA damage in the rat brain regions occurs slowly within 24 h; in the hippocampus, this process runs much slower. The number of mtDNA copies in three regions of the rat brain increases with a simultaneous increase in mtDNA heteroplasmy. However, in the hippocampus, the copy number of mutant mtDNAs increases significantly by the time point of 24 h after radiation exposure. Our analysis shows that in the brain regions of irradiated rats, there is a decrease in the expression of genes (ND2, CytB, ATP5O) involved in ATP synthesis, although by the same time point after irradiation, an increase in transcripts of genes regulating mitochondrial biogenesis is observed. On the other hand, analysis of genes that control the dynamics of mitochondria (Mfn1, Fis1) revealed that sharp decrease in gene expression level occurred, only in the hippocampus. Consequently, the structural and functional characteristics of the hippocampus of rats exposed to whole-body radiation can be different, most significantly from those of the other brain regions.

Expression Levels of Two DNA Repair-related Genes under 8 Gy Ionizing Radiation and 100 Mg/Kg Melatonin Delivery In Rat Peripheral Blood

BACKGROUND

After radiation therapy (RT), some health hazards including DNA damages may occur where melatonin can play a protective role due to free radical generation. On the other hand, serious accidental overexposures may occur during RT due to nuclear accidents which necessitate the need for study on exposure to high-dose radiations during treatments.

OBJECTIVE

The aim of this study was to study the expression level of two genes in non-homologous end joining (NHEJ) pathways named Xrcc4 and Xrcc6 (Ku70) in order to examine the effect of melatonin on repair of DNA double-strand breaks (BSBs) caused by 8Gy ionizing radiation.

METHODS

One hundred eight male Wistar rats were irradiated with a whole body gamma radiation dose of 8Gy with or without melatonin pretreatments. They were divided into six different groups of control, 100 mg/kg melatonin alone, 8Gy irradiation alone, vehicle alone, vehicle plus 8Gy irradiation and 100 mg/kg melatonin plus 8Gy irradiation. Peripheral blood samples were collected at 8, 24 and 48 h after irradiation. Ku70 and Xrcc4 gene expression were evaluated by real-time quantitative polymerase chain reaction (qPCR) technique and analyzed by one-way ANOVA test.

RESULTS

Expression of Ku70 and Xrcc4 genes normalized against Hprt gene showed significant difference in melatonin plus irradiation group at 8h compared to the control group (p<0.05). At 24h post irradiation, gene expression changes were significantly upregulated in irradiation-alone group as well as melatonin plus irradiation group (p<0.05). No significant change was found in any groups compared to control group at 48 h time point.

CONCLUSION

We concluded that, by increasing expression level of Ku70 and Xrcc4 genes, 100 mg/kg melatonin administration 8 and 24 h before 8 Gyionizing radiation can significantly affect the repair of DNA DSBs in NHEJ pathway.

Mechanistic Modelling and Bayesian Inference Elucidates the Variable Dynamics of Double-Strand Break Repair

DNA double-strand breaks are lesions that form during metabolism, DNA replication and exposure to mutagens. When a double-strand break occurs one of a number of repair mechanisms is recruited, all of which have differing propensities for mutational events. Despite DNA repair being of crucial importance, the relative contribution of these mechanisms and their regulatory interactions remain to be fully elucidated. Understanding these mutational processes will have a profound impact on our knowledge of genomic instability, with implications across health, disease and evolution. Here we present a new method to model the combined activation of non-homologous end joining, single strand annealing and alternative end joining, following exposure to ionising radiation. We use Bayesian statistics to integrate eight biological data sets of double-strand break repair curves under varying genetic knockouts and confirm that our model is predictive by re-simulating and comparing to additional data. Analysis of the model suggests that there are at least three disjoint modes of repair, which we assign as fast, slow and intermediate. Our results show that when multiple data sets are combined, the rate for intermediate repair is variable amongst genetic knockouts. Further analysis suggests that the ratio between slow and intermediate repair depends on the presence or absence of DNA-PKcs and Ku70, which implies that non-homologous end joining and alternative end joining are not independent. Finally, we consider the proportion of double-strand breaks within each mechanism as a time series and predict activity as a function of repair rate. We outline how our insights can be directly tested using imaging and sequencing techniques and conclude that there is evidence of variable dynamics in alternative repair pathways. Our approach is an important step towards providing a unifying theoretical framework for the dynamics of DNA repair processes.

Long-term outcome of changes in cognitive function of young rats after various/different doses of whole brain irradiation

OBJECTIVE

To characterize the early delayed and late-delayed cognitive dysfunction induced by various doses of whole brain irradiation in young rats.

METHODS

One-month-old Sprague-Dawley male rats were divided randomly into the 0 (control), 0 (anesthesia control), 2, 10, 20, and 30-Gy groups. Each group was then subdivided into 4 groups according to the experimental intervals: 1, 2, 3, and 6 months after radiation. Rats were irradiated using a 4-MeV electron beam, which was generated by a linear accelerator. Sequential behavioral tests, including open field, novel location and novel object recognition and Morris water maze were performed after radiation. Changes in gross neurological symptoms, body weight, topical skin response, and histopathology were observed.

RESULTS

In the open field test, there were no radiation-induced alterations found. In the novel location and novel object recognition tests, rats of the 20-Gy group spent less time exploring the novel object and novel location 3 months after irradiation. During the place navigation test, the spatial working memory of the 30 and 20-Gy irradiated rats were impaired from 1 to 2 months after irradiation, respectively. In the spatial probe test, the 20 and 30-Gy irradiated rats spent less time in the critical region compared to control rats at 3 and 6 months post-irradiation. Morphological changes, including edema, vascular dilation, focal necrosis, demyelination, and adjacent reactive gliosis were observed in the 30-Gy irradiation group.

CONCLUSION

More than 20 Gy of whole brain irradiation dose can cause significant cognitive dysfunction in young rats.

Long-term Autophagy and Nrf2 Signaling in the Hippocampi of Developing Mice after Carbon Ion Exposure

To explore charged particle radiation-induced long-term hippocampus damage, we investigated the expression of autophagy and antioxidant Nrf2 signaling-related proteins in the mouse hippocampus after carbon ion radiation. Heads of immature female Balb/c mice were irradiated with carbon ions of different LETs at various doses. Behavioral tests were performed on the mice after maturation. Acute and chronic expression of LC3-II, p62/SQSTM1, nuclear Nrf2, activated caspase-3 and the Bax/Bcl-2 ratio were measured in the hippocampi. Secondary X-ray insult was adopted to amplify potential damages. Long-term behavioral changes were observed in high-LET carbon ion-irradiated mice. There were no differences in the rates of LC3-II induction and p62/SQSTM1 degradation compared to the control group regardless of whether the mice received the secondary X-ray insult. A high nuclear Nrf2 content and low apoptosis level in hippocampal cells subjected to secondary X-rays were observed for the mice exposed to relatively low-LET carbon ions. Therefore, carbon ion exposure in the immature mouse led to an LET-dependent behavioral change after maturation. Although autophagy was intact, the persistently high nuclear Nrf2 content in the hippocampus might account for the unchanged behavioral pattern in mice exposed to the relatively low-LET carbon ions and the subsequent increased radioresistance of the hippocampus.

Hippocampal-dependent neurocognitive impairment following cranial irradiation observed in pre-clinical models: current knowledge and possible future directions

We reviewed the literature for studies pertaining to impaired adult neurogenesis leading to neurocognitive impairment following cranial irradiation in rodent models. This compendium was compared with respect to radiation dose, converted to equivalent dose in 2 Gy fractions (EQD2) to allow for direct comparison between studies. The effects of differences between animal species and the dependence on animal age as well as for time after irradiation were also considered. One of the major sites of de novo adult neurogenesis is the hippocampus, and as such, this review also focuses on assessing evidence related to the expression and potential effects of inflammatory cytokines on neural stem cells in the subgranular zone of the dentate gyrus and whether this correlates with neurocognitive impairment. This review also discusses potential strategies to mitigate the detrimental effects on neurogenesis and neurocognition resulting from cranial irradiation, and how the rationale for these strategies compares with the current outcome of pre-clinical studies.

Electroacupuncture prevents cognitive impairments by regulating the early changes after brain irradiation in rats

Cognitive impairments severely affect the quality of life of patients who undergo brain irradiation, and there are no effective preventive strategies. In this study, we examined the therapeutic potential of electroacupuncture (EA) administered immediately after brain irradiation in rats. We detected changes in cognitive function, neurogenesis, and synaptic density at different time points after irradiation, but found that EA could protect the blood-brain barrier (BBB), inhibit neuroinflammatory cytokine expression, upregulate angiogenic cytokine expression, and modulate the levels of neurotransmitter receptors and neuropeptides in the early phase. Moreover, EA protected spatial memory and recognition in the delayed phase. At the cellular/molecular level, the preventative effect of EA on cognitive dysfunction was not dependent on hippocampal neurogenesis; rather, it was related to synaptophysin expression. Our results suggest that EA applied immediately after brain irradiation can prevent cognitive impairments by protecting against the early changes induced by irradiation and may be a novel approach for preventing or ameliorating cognitive impairments in patients with brain tumors who require radiotherapy.

Minocycline ameliorates cognitive impairment induced by whole-brain irradiation: an animal study

Background

It has been long recognized that cranial irradiation used for the treatment of primary and metastatic brain tumor often causes neurological side-effects such as intellectual impairment, memory loss and dementia, especially in children patients. Our previous study has demonstrated that whole-brain irradiation (WBI) can cause cognitive decline in rats. Minocycline is an antibiotic that has shown neuroprotective properties in a variety of experimental models of neurological diseases. However, whether minocycline can ameliorate cognitive impairment induced by ionizing radiation (IR) has not been tested. Thus this study aimed to demonstrate the potential implication of minocycline in the treatment of WBI-induced cognitive deficits by using a rat model.

Methods

Sprague Dawley rats were cranial irradiated with electron beams delivered by a linear accelerator with a single dose of 20 Gy. Minocycline was administered via oral gavages directly into the stomach before and after irradiation. The open field test was used to assess the anxiety level of rats. The Morris water maze (MWM) was used to assess the spatial learning and memory of rats. The level of apoptosis in hippocampal neurons was measured using immunohistochemistry for caspase-3 and relative markers for mature neurons (NeuN) or for newborn neurons (Doublecortin (DCX)). Neurogenesis was determined by BrdU incorporation method.

Results

Neither WBI nor minocycline affected the locomotor activity and anxiety level of rats. However, compared with the sham-irradiated controls, WBI caused a significant loss of learning and memory manifest as longer latency to reach the hidden platform in the MWM task. Minocycline intervention significantly improved the memory retention of irradiated rats. Although minocycline did not rescue neurogenesis deficit caused by WBI 2 months post-IR, it did significantly decreased WBI-induced apoptosis in the DCX positive neurons, thereby resulting in less newborn neuron depletion 12 h after irradiation.

Conclusions

Minocycline significantly inhibits WBI-induced neuron apoptosis, leading to less newborn neurons loss shortly after irradiation. In the long run, minocycline improves the cognitive performance of rats post WBI. The results indicate a potential clinical implication of minocycline as an effective adjunct in radiotherapy for brain tumor patients.

Forced running exercise attenuates hippocampal neurogenesis impairment and the neurocognitive deficits induced by whole-brain irradiation via the BDNF-mediated pathway

Cranial radiotherapy induces progressive and debilitating cognitive deficits, particularly in long-term cancer survivors, which may in part be caused by the reduction of hippocampal neurogenesis. Previous studies suggested that voluntary exercise can reduce the cognitive impairment caused by radiation therapy. However, there is no study on the effect of forced wheel exercise and little is known about the molecular mechanisms mediating the effect of exercise. In the present study, we investigated whether the forced running exercise after irradiation had the protective effects of the radiation-induced cognitive impairment. Sixty-four Male Sprague-Dawley rats received a single dose of 20Gy or sham whole-brain irradiation (WBI), behavioral test was evaluated using open field test and Morris water maze at 2months after irradiation. Half of the rats accepted a 3-week forced running exercise before the behavior detection. Immunofluorescence was used to evaluate the changes in hippocampal neurogenesis and Western blotting was used to assess changes in the levels of mature brain-derived neurotrophic factor (BDNF), phosphorylated tyrosine receptor kinase B (TrkB) receptor, protein kinase B (Akt), extracellular signal-regulated kinase (ERK), calcium-calmodulin dependent kinase (CaMKII), cAMP-calcium response element binding protein (CREB) in the BDNF-pCREB signaling. We found forced running exercise significantly prevented radiation-induced cognitive deficits, ameliorated the impairment of hippocampal neurogenesis and attenuated the down-regulation of these proteins. Moreover, exercise also increased behavioral performance, hippocampal neurogenesis and elevated BDNF-pCREB signaling in non-irradiation group. These results suggest that forced running exercise offers a potentially effective treatment for radiation-induced cognitive deficits.

Short-course radiotherapy in elderly patients with glioblastoma: feasibility and efficacy of results from a single centre

BACKGROUND

The incidence of glioblastoma (GBM) in the elderly population is currently increasing, with a peak seen between 65 and 84 years. The optimal treatment in terms of both efficacy and quality of life still remains a relevant and debated issue today. The purpose of our study was to evaluate the feasibility of short-course hypofractionated accelerated radiotherapy (HART) in GBM patients aged over 70 years and with a good Karnofsky performance score (KPS).

METHODS

A review of medical records at the "Istituto Neurologico C. Besta" was undertaken; patients aged ≥ 70 years who had undergone adjuvant HART for GBM between January 2000 and January 2004 were included in the study. HART was administered to a total dose of 45 Gy, 2.5 Gy/fraction, in three daily fractions for three consecutive days/cycle fractions each, delivered in two cycles (split 15 days).

RESULTS

A total of 33 patients were evaluable for the current analysis. Median follow-up was 10 months. According to CTCAE (version 3.0) criteria, none of the patients developed radiation-induced neurological status deterioration or necrosis. KPS evaluation after HART was found to be stable in 73 % of patients, improved in 24 %, and worse in 3 %. The median overall survival time of the entire study population was 8 months (range 2-24).

CONCLUSIONS

Our findings suggest that a hypofractionated accelerated schedule can be a safe and effective option in the treatment of GBM in the elderly.