New routes in frontotemporal dementia drug discovery

Introduction: Research into the pathogenic mechanisms behind frontotemporal dementia (FTD) has yielded several new targets for therapeutic intervention; such targets include specific new pathways uncovered by mutations as well as targets involving the modulation, formation and degradation of protein aggregates.

Areas covered: Herein, the authors outline the principal molecular causes underlying FTD to date and the research that has been performed in these areas with respect to an eventual corrective strategy.

Expert opinion: While it is worthwhile targeting pathways affected by specific mutations with a causative loss of function linked to FTD, research still has to contend with issues including the remaining presence of protein aggregates or that treatments are rarely universally applicable. Aiming to recover function in a downstream target caused by the protein aggregates will likely be insufficient due to the large cascade of events affected. It is our belief that the clearance of these aggregates and the inhibition of protein misfolding are more appropriate and direct routes to an eventual therapy.     

连接蛋白43在骨关节炎发病机制中的研究进展

骨关节炎(osteoarthritis,OA)是常见的关节疾病,也是导致残疾的主要原因之一,给患者及家庭带来巨大的经济生活负担。虽然OA的发病机制至今尚未完全明确,但关节软骨代谢平衡的破坏被认为与骨关节炎的发生息息相关。研究发现连接蛋白43(connexin43)在维持关节软骨代谢平衡的稳态中发挥着至关重要的作用,它所参与形成的半通道(hemichannels)和缝隙连接(gap junctions)在细胞与细胞外基质,以及细胞之间建立起直接的物质信号交换通道。同时,连接蛋白43的高表达和(或)分布的变化都将影响软骨细胞结构和功能的完整性。因此,连接蛋白43被认为与骨关节炎的发生有着密切关系。本文就连接蛋白43与骨关节炎发病机制的研究进展做一综述。     

Mechanism of Regulatory Effect of MicroRNA-206 on Connexin 43 in Distant Metastasis of Breast Cancer

Background:

MicroRNA-206 (miR-206) and connexin 43 (Cx43) are related with the distant metastasis of breast cancer. It remains unclear whether the regulatory effect of miR-206 on Cx43 is involved in metastasis of breast cancer.

Methods:

Using quantitative real-time polymerase chain reaction and Western blot, the expressions of miR-206 and Cx43 were determined in breast cancer tissues, hepatic and pulmonary metastasis (PM), and cell lines (MCF-10A, MCF-7, and MDA-MB-231). MCF-7/MDA-M-231 cells were transfected with lentivirus-shRNA vectors to enhance/inhibit miR-206, and then Cx43 expression was observed. Cell counting kit-8 assay and Transwell method were used to detect their changes in proliferation, migration, and invasion activity. The mutant plasmids of Cx43-3’ untranslated region (3’UTR) at position 478–484 and position 1609–1615 were constructed. Luciferase reporter assay was performed to observe the effects of miR-206 on luciferase expression of different mutant plasmids and to confirm the potential binding sites of Cx43.

Results:

Cx43 protein expression in hepatic and PM was significantly higher than that in the primary tumor, while no significant difference was showed in messenger RNA (mRNA) expression. MiR-206 mRNA expression in hepatic and PM was significantly lower than that in the primary tumor. Cx43 mRNA and protein levels, as well as cell proliferation, migration, and invasion capabilities, were all significantly improved in MDA-MB-231 cells after reducing miR-206 expression but decreased in MCF-7 cells after elevating miR-206 expression, which demonstrated a significantly negative correlation between miR-206 and Cx43 expression (P = 0.03). MiR-206 can drastically decrease Cx43 expression of MCF-7 cells but exerts no effects on Cx43 expression in 293 cells transfected with the Cx43 coding region but the lack of Cx43-3’UTR, suggesting that Cx43-3’UTR may be the key in Cx43 regulated by miR-206. Luciferase expression showed that the inhibition efficiency was reduced by 46.80% in position 478–484 mutant, 16.72% in position 1609–1615 mutant; the inhibition was totally disappeared in double mutant (P = 0.02).

Conclusions:

MiR-206 can regulate the expression of Cx43, the cytobiological activity, and the metastasis of breast cancer through binding to the two binding sites in Cx43-3’UTR: position 478–484 and position 1609–1615.     

Chronic antidepressant treatment selectively increases expression of plasticity-related proteins in the hippocampus and medial prefrontal cortex of the rat

Antidepressants protect against hippocampal volume loss in humans and reverse stress-induced atrophic changes in animals thus supporting the hypothesis that the pathophysiology of stress-related disorders such as depression involves reductions in neuronal connectivity and this effect is reversible by antidepressant treatment. However, it is unclear which brain areas demonstrate such alterations in plasticity in response to antidepressant treatment. The aim of the present study was to examine the effect of antidepressant treatment on the expression of three plasticity-associated marker proteins, the polysialylated form of nerve cell adhesion molecule (PSA-NCAM), phosphorylated cyclic-AMP response element binding protein (pCREB) and growth-associated protein 43 (GAP-43), in the rat brain. To this end, rats were treated either acutely (60 min) or chronically (21 days) with imipramine (30 and 15 mg/kg, respectively) and the expression of PSA-NCAM, pCREB, and GAP-43 was assessed using immunohistochemistry. Initial mapping revealed that chronic imipramine treatment increased expression of these plasticity-associated proteins in the hippocampus, medial prefrontal cortex and piriform cortex but not in the other brain regions examined. Since PSA-NCAM and pCREB are expressed in recently-generated neurons in the dentate gyrus, it is likely that chronic imipramine treatment increased their expression in the hippocampus at least partially by increasing neurogenesis. In contrast, since chronic imipramine treatment is not associated with neurogenesis in the medial prefrontal cortex, increased expression of PSA-NCAM and pCREB in the prelimbic cortex implicates changes in synaptic connectivity in this brain region. Acute treatment with imipramine increased the number of pCREB positive nuclei in the hippocampus and the prefrontal cortex but did not alter expression of GAP-43 or PSA-NCAM in any of the brain regions examined. Taken together, the results of the present study suggest that antidepressant treatment increases synaptic plasticity and connectivity in brain regions associated with mood disorders.     

Connexin 43 Is Necessary for Murine Tendon Enthesis Formation and Response to Loading

The enthesis is a mineralized fibrocartilage transition that attaches tendon to bone and is vital for musculoskeletal function. Despite recent studies demonstrating the necessity of muscle loading for enthesis formation, the mechanisms that regulate enthesis formation and mechanoresponsiveness remain unclear. Therefore, the current study investigated the role of the gap junction protein connexin 43 in these processes by deleting Gja1 (the Cx43 gene) in the tendon and enthesis. Compared with their wild-type (WT) counterparts, mice lacking Cx43 showed disrupted entheseal cell alignment, reduced mineralized fibrocartilage, and impaired biomechanical properties of the supraspinatus tendon entheses during postnatal development. Cx43-deficient mice also exhibited reduced ability to complete a treadmill running protocol but no apparent deficits in daily activity, metabolic indexes, shoulder muscle size, grip strength, and major trabecular bone properties of the adjacent humeral head. To examine enthesis mechanoresponsiveness, young adult mice were subjected to modest treadmill exercise. Gja1 deficiency in the tendon and enthesis reduced entheseal anabolic responses to treadmill exercise: WT mice had increased expression of Sox9, Ihh, and Gli1 and increased Brdu incorporation, whereas Cx43-deficient mice showed no changes or decreased levels with exercise. Collectively, the results demonstrated an essential role for Cx43 in postnatal tendon enthesis formation, function, and response to loading; results further provided evidence implicating a link between Cx43 function and the hedgehog signaling pathway. © 2020 American Society for Bone and Mineral Research.     

oxLDL对人脐静脉内皮细胞通透性影响及机制研究

目的探讨氧化低密度脂蛋白（ox LDL）对人脐静脉内皮细胞（HUVECs）通透性的影响及其可能机制。方法采用Transwell单层细胞模型系统和油红O染色,观察ox LDL对单层血管内皮细胞通透性的影响以及THP-1巨噬细胞内脂质的蓄积情况;采用蛋白质印迹法及免疫荧光技术检测ox LDL对HUVECs紧密连接occludin蛋白的表达及分布改变。结果 ox LDL增加单层内皮细胞对LDL的通透性和THP-1巨噬细胞脂质的蓄积;ox LDL降低occludin蛋白的表达,同时免疫荧光染色显示,ox LDL处理后,血管内皮细胞间隙增宽,occludin染色减少或脱失,而抑制氧化应激可以减弱ox LDL对内皮细胞的高通透性反应和occludin蛋白表达和形态学的影响。结论 ox LDL可能是通过occludin蛋白表达下降使内皮细胞构改变来介导内皮通透性增加,从而促进内皮下巨噬细胞内的脂质蓄积。     

Bunina bodies in motor and non‐motor neurons revisited: A pathological study of an ALS patient after long‐term survival on a respirator

Bunina bodies (BBs) are small eosinophilic neuronal cytoplasmic inclusions (NCIs) found in the remaining lower motor neurons (LMNs) of patients with sporadic amyotrophic lateral sclerosis (SALS), being a specific feature of the cellular pathology. We examined a case of SALS, unassociated with TDP‐43 or C9ORF72 mutation, of 12 years duration in a 75‐year‐old man, who had received artificial respiratory support for 9 years, and showed widespread multisystem degeneration with TDP‐43 pathology. Interestingly, in this patient, many NCIs reminiscent of BBs were observed in the oculomotor nucleus, medullary reticular formation and cerebellar dentate nucleus. As BBs in the cerebellar dentate nucleus have not been previously described, we performed ultrastructural and immunohistochemical studies of these NCIs to gain further insight into the nature of BBs. In each region, the ultrastructural features of these NCIs were shown to be identical to those of BBs previously described in LMNs. These three regions and the relatively well preserved sacral anterior horns (S1 and S2) and facial motor nucleus were immunostained with antibodies against cystatin C (CC) and TDP‐43. Importantly, it was revealed that BBs exhibiting immunoreactivity for CC were a feature of LMNs, but not of non‐motor neurons, and that in the cerebellar dentate nucleus, the ratio of neurons with BBs and TDP‐43 inclusions/neurons with BBs was significantly lower than in other regions. These findings suggest that the occurrence of BBs with CC immunoreactivity is intrinsically associated with the particular cellular properties of LMNs, and that the mechanism responsible for the formation of BBs is distinct from that for TDP‐43 inclusions.     

Is synaptic loss a unique hallmark of Alzheimer's disease?

Synapses may represent a key nidus for dementia including Alzheimer's disease (AD) pathogenesis. Here we review published studies and present new ideas related to the question of the specificity of synapse loss in AD. Currently, AD is defined by the regional presence of neuritic plaques and neurofibrillary tangles in the brain. The severity of involvement by those pathological hallmarks tends to correlate both with antemortem cognitive status, and also with synapse loss in multiple brain areas. Recent studies from large autopsy series have led to a new standard of excellence with regard to clinical–pathological correlation and to improved comprehension of the numerous brain diseases of the elderly. These studies have provided evidence that it is the rule rather than the exception for brains of aged individuals to demonstrate pathologies (often multiple) other than AD plaques and tangles. For many of these comorbid pathologies, the extent of synapse loss is imperfectly understood but could be substantial. These findings indicate that synapse loss is probably not a hallmark specific to AD but rather a change common to many diseases associated with dementia.     

The Portal Vertex of KSHV Promotes Docking of Capsids at the Nuclear Pores

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a cancer-related herpesvirus. Like other herpesviruses, the KSHV icosahedral capsid includes a portal vertex, composed of 12 protein subunits encoded by open reading frame (ORF) 43, which enables packaging and release of the viral genome into the nucleus through the nuclear pore complex (NPC). Capsid vertex-specific component (CVSC) tegument proteins, which directly mediate docking at the NPCs, are organized on the capsid vertices and are enriched on the portal vertex. Whether and how the portal vertex is selected for docking at the NPC is unknown. Here, we investigated the docking of incoming ORF43-null KSHV capsids at the NPCs, and describe a significantly lower fraction of capsids attached to the nuclear envelope compared to wild-type (WT) capsids. Like WT capsids, nuclear envelope-associated ORF43-null capsids co-localized with different nucleoporins (Nups) and did not detach upon salt treatment. Inhibition of nuclear export did not alter WT capsid docking. As ORF43-null capsids exhibit lower extent of association with the NPCs, we conclude that although not essential, the portal has a role in mediating the interaction of the CVSC proteins with Nups, and suggest a model whereby WT capsids can dock at the nuclear envelope through a non-portal penton vertex, resulting in an infection ‘dead end’.