Increased expression of prohormone convertase-2 in the irradiated rat brain

Early-life adversity alters adult nucleus incertus neurons: implications for neuronal mechanisms of increased stress and compulsive behavior vulnerability

Early-life stress (ELS) arising from physical and emotional abuse disrupts normal brain development and impairs hypothalamic-pituitary-adrenal axis function, increasing the risk of psychopathological disorders and compulsive behaviors in adulthood. However, the underlying neural mechanisms remain unclear. The brainstem nucleus incertus (NI) is a highly stress-sensitive locus, involved in behavioral activation and stress-induced reward (food/alcohol) seeking, but its sensitivity to ELS remains unexplored. We used neonatal maternal separation stress in rats as a model for ELS and examined its impact on stress-related mRNA and neuropeptide expression in the NI, using fluorescent in situ hybridization and immunohistochemistry, respectively. Using whole-cell, patch-clamp recordings we determined the influence of ELS on the synaptic activity, excitability, and electrophysiological properties of NI neurons. Using c-Fos protein expression we also assessed the impact of ELS on the sensitivity of NI neurons to acute restraint stress in adulthood. ELS weakened the acute stress responsiveness of NI neurons, and caused dendritic shrinkage, impaired synaptic transmission and altered electrophysiological properties of NI neurons in a cell-type-specific manner. Additionally, ELS increased the expression of mRNA encoding corticotropin-releasing hormone receptor type 1 and the nerve-growth factor receptor, TrkA in adult NI. The multiple, cell-type specific changes in the expression of neuropeptides and molecules associated with stress and substance abuse in the NI, as well as impairments in NI neuron morphology and electrophysiology caused by ELS and observed in the adult brain, may contribute to the increased susceptibility to stress and compulsive behaviors observed in individuals with a history of ELS.

The transcriptomic revolution and radiation biology

PURPOSE

This article will briefly review the origins and evolution of functional genomics, first describing the experimental technology, and then some of the approaches applied to data analysis and visualization. It will emphasize application of functional genomics to radiation biology, using examples from the author's work to illustrate several key types of analysis. It concludes with a look at non-coding RNA, alternative reading of the genome, and single-cell transcriptomics, some of the innovative areas that may help to shape future research in radiation biology and oncology.

CONCLUSIONS

Transcriptomic approaches have provided insight into many areas of radiation biology and medicine, and innovations in technology and data analysis approaches promise continued contributions to radiation science in the future.

Molecular, Cellular and Functional Effects of Radiation-Induced Brain Injury: A Review

Radiation therapy is the most effective non-surgical treatment of primary brain tumors and metastases. Preclinical studies have provided valuable insights into pathogenesis of radiation-induced injury to the central nervous system. Radiation-induced brain injury can damage neuronal, glial and vascular compartments of the brain and may lead to molecular, cellular and functional changes. Given its central role in memory and adult neurogenesis, the majority of studies have focused on the hippocampus. These findings suggested that hippocampal avoidance in cranial radiotherapy prevents radiation-induced cognitive impairment of patients. However, multiple rodent studies have shown that this problem is more complex. As the radiation-induced cognitive impairment reflects hippocampal and non-hippocampal compartments, it is of critical importance to investigate molecular, cellular and functional modifications in various brain regions as well as their integration at clinically relevant doses and schedules. We here provide a literature overview, including our previously published results, in order to support the translation of preclinical findings to clinical practice, and improve the physical and mental status of patients with brain tumors.

Radiation-induced brain injury: A review

Approximately 100,000 primary and metastatic brain tumor patients/year in the US survive long enough (>6 months) to experience radiation-induced brain injury. Prior to 1970, the human brain was thought to be highly radioresistant; the acute CNS syndrome occurs after single doses >30 Gy; white matter necrosis occurs at fractionated doses >60 Gy. Although white matter necrosis is uncommon with modern techniques, functional deficits, including progressive impairments in memory, attention, and executive function have become important, because they have profound effects on quality of life. Preclinical studies have provided valuable insights into the pathogenesis of radiation-induced cognitive impairment. Given its central role in memory and neurogenesis, the majority of these studies have focused on the hippocampus. Irradiating pediatric and young adult rodent brains leads to several hippocampal changes including neuroinflammation and a marked reduction in neurogenesis. These data have been interpreted to suggest that shielding the hippocampus will prevent clinical radiation-induced cognitive impairment. However, this interpretation may be overly simplistic. Studies using older rodents, that more closely match the adult human brain tumor population, indicate that, unlike pediatric and young adult rats, older rats fail to show a radiation-induced decrease in neurogenesis or a loss of mature neurons. Nevertheless, older rats still exhibit cognitive impairment. This occurs in the absence of demyelination and/or white matter necrosis similar to what is observed clinically, suggesting that more subtle molecular, cellular and/or microanatomic modifications are involved in this radiation-induced brain injury. Given that radiation-induced cognitive impairment likely reflects damage to both hippocampal- and non-hippocampal-dependent domains, there is a critical need to investigate the microanatomic and functional effects of radiation in various brain regions as well as their integration at clinically relevant doses and schedules. Recently developed techniques in neuroscience and neuroimaging provide not only an opportunity to accomplish this, but they also offer the opportunity to identify new biomarkers and new targets for interventions to prevent or ameliorate these late effects.

Dragon's blood may have radioprotective effects in radiation-induced rat brain injury

Dragon's blood is a bright red resin obtained from Dracaena cochinchinensis. It is a traditional medicinal that is used for wound healing and to stop bleeding. Its main biological activity appears to be from phenolic compounds found in Dragon's blood. In this study, the radioprotective effects of Dragon's blood were examined after whole brain irradiation of rats with either 100 MeV/u Carbon (12)C(6+) heavy ions or (60)Co γ-rays. The amounts of radiation-induced oxidative stress, inflammatory cytokines and apoptosis in irradiated rat brains were compared with and without Dragon's blood treatment. Compared to the "irradiation only" control group, the Dragon's blood treatment group significantly decreased malondialdehyde and hydrogen peroxide levels, and increased superoxide dismutase activity and glutathione levels induced by oxidative stress in radiation exposed rats (P < 0.05). Dragon's blood also significantly reduced radiation-induced inflammatory cytokines of tumor necrosis factor-α, interferon-γ and interleukin-6 levels (P < 0.05) and inhibited hippocampal neuronal apoptosis in (60)Co γ-ray irradiated rats. Furthermore, Dragon's blood significantly increased expression of brain-derived neurophic factor and inhibited the expression of pro-apoptotic caspase 3 (P < 0.05-0.01). Finally, Dragon's blood significantly inhibited expression of the AP-1 transcription factor family members c-fos and c-jun proteins (P < 0.05-0.01). The results obtained here suggest that Dragon's blood has radioprotective properties in rat brains after both heavy ions and (60)Co γ-ray exposure.

Renin-angiotensin system blockers and modulation of radiation-induced brain injury

Radiation-induced brain injury remains a major cause of morbidity in cancer patients with primary or metastatic brain tumors. Approximately 200,000 individuals/year are treated with fractionated partial or whole-brain irradiation, and > half will survive long enough (≤6 months) to develop radiation-induced brain injury, including cognitive impairment. Although short-term treatments have shown efficacy, no long-term treatments or preventive approaches are presently available for modulating radiation-induced brain injury. Based on previous preclinical studies clearly demonstrating that renin-angiotensin system (RAS) blockers can modulate radiation-induced late effects in the kidney and lung, we and others hypothesized that RAS blockade would similarly modulate radiation-induced brain injury. Indeed, studies in the last 5 years have shown that both angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II type 1 receptor antagonists (AT(1)RAs) can prevent/ameliorate radiation-induced brain injury, including cognitive impairment, in the rat. The mechanistic basis for this RAS blocker-mediated effect remains the subject of ongoing investigations. Putative mechanisms include, i] blockade of Ang II/NADPH oxidase-mediated oxidative stress and neuroinflammation, and ii] a change in the balance of angiotensin (Ang) peptides from the pro-inflammatory and pro-oxidative Ang II to the anti-inflammatory and anti-oxidative Ang-1-7). However, given that both ACEIs and AT(1)RAs are 1] well-tolerated drugs routinely prescribed for hypertension, 2] exhibit some antitumor properties, and 3] can prevent/ameliorate radiation-induced brain injury, they appear to be ideal drugs for future clinical trials, offering the promise of improving the quality of life of brain tumor patients receiving brain irradiation.

Defective neuropeptide processing and ischemic brain injury: a study on proprotein convertase 2 and its substrate neuropeptide in ischemic brains

Using a focal cerebral ischemia model in rats, brain ischemia-induced changes in expression levels of mRNA and protein, and activities of proprotein convertase 2 (PC2) in the cortex were examined. In situ hybridization analyses revealed a transient upregulation of the mRNA level for PC2 at an early reperfusion hour, at which the level of PC2 protein was also high as determined by immunocytochemistry and western blotting. When enzymatic activities of PC2 were analyzed using a synthetic substrate, a significant decrease was observed at early reperfusion hours at which levels of PC2 protein were still high. Also decreased at these reperfusion hours were tissue levels of dynorphin-A(1-8) (DYN-A(1-8)), a PC2 substrate, as determined by radioimmunoassay. Further examination of PC2 protein biosynthesis by metabolic labeling in cultured neuronal cells showed that in ischemic cells, the proteolytic processing of PC2 was greatly attenuated. Finally, in mice, an intracerebroventricular administration of synthetic DYN-A(1-8) significantly reduced the extent of ischemic brain injury. In mice those lack an active PC2, exacerbated brain injury was observed after an otherwise non-lethal focal ischemia. We conclude that brain ischemia attenuates PC2 and PC2-mediated neuropeptide processing. This attenuation may play a role in the pathology of ischemic brain injury.

Stereotactic radiosurgery: adjacent tissue injury and response after high-dose single fraction radiation: Part I--Histology, imaging, and molecular events

Radiosurgery is now the preferred treatment modality for many intracranial disease processes. Although almost 50 years have passed since it was introduced as a tool to treat neurological disease, investigations into its effects on normal tissues of the central nervous system are still ongoing. The need for these continuing studies must be underscored. A fundamental understanding of the brain parenchymal response to radiosurgery would permit development of strategies that would enhance and potentiate the radiosurgical treatment effects on diseased tissue while mitigating injury to normal structures. To date, most studies on the response of the central nervous system to radiosurgery have been performed on brain tissue in the absence of pathological lesions, such as benign tumors or metastases. Although instructive, these investigations fail to emulate the majority of clinical scenarios that involve radiosurgical treatment of specific lesions surrounded by normal brain parenchyma. This article is the first in a two-part series that addresses the brain parenchyma's response to radiosurgery. This first article analyzes the histological, radiographic, and molecular data gathered regarding the brain parenchymal response to radiosurgery and aims to suggest future studies that could enhance our understanding of the topic. The second article in the series begins by discussing strategies for radiosurgical therapeutic enhancement. It concludes by focusing on strategies for mitigation and repair of radiation-induced brain injury.

Altered biosynthesis of neuropeptide processing enzyme carboxypeptidase E after brain ischemia: molecular mechanism and implication

In this study, using both in vivo and in vitro ischemia models, the authors investigated the impact of brain ischemia on the biosynthesis of a key neuropeptide-processing enzyme, carboxypeptidase E (CPE). The response to brain ischemia of animals that lacked an active CPE was also examined. Combined in situ hybridization and immunocytochemical analyses for CPE showed reciprocal changes of CPE mRNA and protein, respectively, in the same cortical cells in rat brains after focal cerebral ischemia. Western blot analysis revealed an accumulation of the precursor protein of CPE in the ischemic cortex in vivo and in ischemic cortical neurons in vitro. Detailed metabolic labeling experiments on ischemic cortical neurons showed that ischemic stress caused a blockade in the proteolytic processing of CPE. When mice lacking an active CPE protease were subjected to a sublethal episode of focal cerebral ischemia, abundant TUNEL-positive cells were seen in the ischemic cortex whereas only a few were seen in the cortex of wild-type animals. These findings suggest that ischemia has an adverse impact on the neuropeptide-processing system in the brain and that the lack of an active neuropeptide-processing enzyme exacerbates ischemic brain injury.

Characterization of a repressor element in the promoter region of proprotein convertase 2 (PC2) gene

The proprotein convertase PC2 is primarily expressed in neuroendocrine cells where it mediates the proteolytic maturation of prohormones and proneuropeptides. We have identified in the upstream sequence of its gene a conserved domain partially homologous to the repressor element RE1/NRSE found in several genes for neuronal proteins. RE1/NRSE binds the silencing transcription factor REST/NRSF, a nuclear protein primarily found in nonneuronal cells. To determine the functionality of the PC2 gene RE1-like sequence (RE1-lk), we examined by electrophoretic mobility shift assays its ability to attach nuclear factors from PC2-expressing and nonexpressing cells. Specific binding factors were mostly detectable in PC2-non-expressing cells. These factors differ from REST/NRSF, as molar excess of competing RE1/NRSE could not prevent their binding to RE1-lk. Reciprocally, molar excess of RE1-lk could not prevent the binding of RE1/NRSE to the DNA-binding domain of a recombinant REST/NRSF. The presence of RE1-lk in cis reduced the ability of the PC2 promoter and the heterologous phosphoglycerate kinase promoter to drive expression of a green fluorescent protein reporter gene in transiently transfected PC2-nonexpressing cells, but not in PC2-expressing cells. These observations suggest that binding of transcription-silencing factors to the RE1-lk element may contribute to repression of the PC2 gene in nonneuroendocrine cells.

The radioresponse of the central nervous system: a dynamic process

Radiation continues to be a major treatment modality for tumors located within and close to the central nervous system (CNS). Consequently, alleviating or protecting against radiation-induced CNS injury would be of benefit in cancer treatment. However, the rational development of such interventional strategies will depend on a more complete understand-ing of the mechanisms responsible for the development of this form of normal tissue injury. Whereas the vasculature and the oligodendrocyte lineage have traditionally been considered the primary radiation targets in the CNS, in this review we suggest that other phenotypes as well as critical cellular interactions may also be involved in determining the radio-response of the CNS. Furthermore, based on the assumption that the CNS has a limited repertoire of responses to injury, the reaction of the CNS to other types of insults is used as a framework for modeling the pathogenesis of radiation-induced damage. Evidence is then provided suggesting that, in addition to acute cell death, radiation induces an intrinsic recovery/repair response in the form of specific cytokines and may

NF kappa B activity and target gene expression in the rat brain after one and two exposures to ionizing radiation

The central nervous system injury that can result after radiotherapy has been suggested to involve induced gene expression and cytokine production. We have previously shown that irradiation of primary cultures of rat astrocytes results in the activation of NF kappa B. To determine whether such an effect also occurs in vivo, NF kappa B activity was analyzed in the cerebral cortex of the rat brain after whole body irradiation. After a single dose of 15 Gy, NF kappa B activity was increased by 2 h postirradiation, returning to unirradiated levels by 8 hours. The increase was dose-dependent beginning at 2 Gy and continuing to at least 22.5 Gy. NF kappa B activity in the irradiated cortex was not accompanied by I kappa B alpha degradation. When 7.5 Gy was delivered 24 h before the 15 Gy, the increase in NF kappa B activity after 15 Gy was significantly reduced. These results suggest that an initial exposure to radiation induced a refractory period in the brain during which the susceptibility of NF kappa B to activation by subsequent irradiation was significantly reduced. This period of reduced sensitivity to radiation was also apparent for the induction of the NF kappa B-regulated cytokines IL-1 beta, IL-6, and TNF alpha.