Highlights from Special Issue: Junctional Targets of Skin and Heart Diseases

Abstract

In this issue, guest editors Kathy Green and Mario Delmar, who are leaders in the fields of epidermal desmosomes and heart intercalated discs respectively, have joined forces to collate a two-part series of reviews focused on junctional proteins and genes that are targets of skin and heart diseases.     

Mosaic RASopathies

“RASopathies” are a group of developmental syndromes with partly overlapping clinical symptoms that are caused by germline mutations of genes within the Ras/MAPK signaling pathway. Mutations affecting this pathway can also occur in a mosaic state, resulting in congenital syndromes often distinct from those generated by the corresponding germline mutations. For syndromes caused by mosaic mutations of the Ras/MAPK signaling pathway, the term “mosaic RASopathies” has been proposed. In the following article, genetic and phenotypic aspects of mosaic RASopathies will be discussed.     

Feedback inhibition of ENaC: Acute and chronic mechanisms

Intracellular [Na⁺] ([Na⁺]_i) modulates the activity of the epithelial Na channel (ENaC) to help prevent cell swelling and regulate epithelial Na⁺ transport, but the underlying mechanisms remain unclear. We show here that short-term (60–80 min) incubation of ENaC-expressing oocytes in high Na⁺ results in a 75% decrease in channel activity. When the β subunit was truncated, corresponding to a gain-of-function mutation found in Liddle's syndrome, the same maneuver reduced activity by 45% despite a larger increase in [Na⁺]_i. In both cases the inhibition occurred with little to no change in cell-surface expression of γENaC. Long-term incubation (18 hours) in high Na⁺ reduced activity by 92% and 75% in wild-type channels and Liddle's mutant, respectively, with concomitant 70% and 52% decreases in cell-surface γENaC. In the presence of Brefeldin A to inhibit forward protein trafficking, high-Na⁺ incubation decreased wt ENaC activity by 52% and 88% after 4 and 8 hour incubations, respectively. Cleaved γENaC at the cell surface had lifetimes at the surface of 6 hrs in low Na⁺ and 4 hrs in high Na⁺, suggesting that [Na⁺]_i increased the rate of retrieval of cleaved γ ENaC by 50%. This implies that enhanced retrieval of ENaC channels at the cell surface accounts for part, but not all, of the downregulation of ENaC activity shown with chronic increases in [Na⁺]_i.     

儿童噬血细胞综合征38例临床分析

摘要目的：探讨噬血细胞综合征患儿的临床特征、治疗及预后。方法：对38例噬血细胞综合征患儿的Il盏床症状、体征、试验检查结果、治疗及预后,进行回顾性总结与分析。结果：38例患儿主要表现为发热、肝脾淋巴结肿大、外周血细胞减少、铁蛋白升高、凝血功能异常;经针对性治疗后,治愈3例,好转20例,疗效不佳自动出院9例,死亡6例。结论：噬血细胞综合征病因复杂,临床表现多种多样,病情凶险,预后较差,旱期诊断及治疗对预后十分关键。     

即刻电针介入对IBS模型大鼠血浆ET,CGRP水平及结肠ETR-A,CGRPmRNA表达的影响

目的：比较即刻电针天枢穴、足三里穴对肠易激综合征（ms）模型大鼠血浆降钙基因相关肽（CGRP）、内皮素（ET）水平及结肠组织中内皮素受体A（ETR－A）、CGRPmRNA表达的影响,旨在探讨电针即刻治疗IBS的部分机制。方法：采用WISTAR幼鼠制备肠易激综合征模型,随机分为空白对照组、模型组、天枢组、足三里组,每组8只。空白对照组不作任何处理,模型组只束缚不针刺,天枢组和足三里组在实验第8周电针治疗一次,留针20min。治疗结束后处死大鼠,取大鼠血浆及部分结肠组织进行生物活性物质检测。采用酶联免疫法检测血浆中CGRP、ET、结肠组织中ETR—A的含量,采用RT—PCR法检测结肠组织中CGRPmRNA表达。结果：（1）即刻电针对IBS模型大鼠血浆CGRP、ET水平的影响：与空白对照组比较,模型组CGRP水平明显降低（P〈0．01）;与模型组比较,天枢组、足三里组CGRP水平明显升高（P〈0．01）。与空白对照组比较,模型组ET水平升高（P〈0．05）;与模型组比较,天枢组ET水平明显降低（P〈0．01）。（2）即刻电针对IBS模型大鼠结肠组织ETR—A水平的影响：与空白对照组比较,模型组ETR—A水平明显升高（P〈0．01）;与模型组比较,足三里组ETR-A水平明显降低（P〈0．01）。（3）即刻电针对IBS模型大鼠结肠组织CGRPmRNA表达的影响：与空白对照组比较,模型组、天枢组、足三里组CGRPmRNA表达明显增强（P〈0．01,P〈0．05）;与模型组比较,足三里组CGRPmRNA表达减弱（P〈0．05）。结论：即刻电针介入后,能够调节机体的内环境紊乱和CGRP、ET的平衡失调。这种调节作用因穴位不同而具有不同的特点,天枢穴对血浆中CGRP、ET调节作用较强,足三里穴在受体和基因表达方面作用明显。     

MLH1 constitutional and somatic methylation in patients with MLH1 negative tumors fulfilling the revised Bethesda criteria

Lynch syndrome (LS) is a tumor predisposing condition caused by constitutional defects in genes coding for components of the mismatch repair (MMR) apparatus. While hypermethylation of the promoter of the MMR gene MLH1 occurs in about 15% of colorectal cancer samples, it has also been observed as a constitutional alteration, in the absence of DNA sequence mutations, in a small number of LS patients. In order to obtain further insights on the phenotypic characteristics of MLH1 epimutation carriers, we investigated the somatic and constitutional MLH1 methylation status of 14 unrelated subjects with a suspicion of LS who were negative for MMR gene constitutional mutations and whose tumors did not express the MLH1 protein. A novel case of constitutional MLH1 epimutation was identified. This patient was affected with multiple primary tumors, including breast cancer, diagnosed starting from the age of 55 y. Investigation of her offspring by allele specific expression revealed that the epimutation was not stable across generations. We also found MLH1 hypermethylation in cancer samples from 4 additional patients who did not have evidence of constitutional defects. These patients had some characteristics of LS, namely early age at onset and/or positive family history, raising the possibility of genetic influences in the establishment of somatic MLH1 methylation.     

Is reactivation of autophagy a possible therapeutic solution for obesity and metabolic syndrome?

The molecular mechanism regulating the cardiomyocyte response to energy stress has been a hot topic in cardiac research in recent years, since this mechanism could be targeted for treatment of patients with ischemic heart disease. We have shown recently that the activity of RAS homolog enriched in brain (RHEB), a small GTP binding protein, is inhibited in response to glucose deprivation (GD) in cardiomyocytes and ischemia in the mouse heart. This is a physiological adaptation, since it inhibits complex 1 of the mechanistic target of rapamycin (MTORC1) and activates autophagy, thereby promoting cell survival during GD and prolonged ischemia. Importantly, the physiological inhibition of RHEB-MTORC1 signaling during myocardial ischemia is impaired in the presence of obesity and metabolic syndrome caused by high-fat diet (HFD) feeding, leading to a dramatic increase in ischemic injury. Although MTORC1 and autophagy can be regulated through RHEB-independent mechanisms, such as the AMPK-dependent phosphorylation of RPTOR and ULK1, RHEB appears to be critical in the regulation of MTORC1 and autophagy during ischemia in cardiomyocytes, and its dysregulation is relevant to human disease. Here we discuss the biological relevance of the dysregulation of RHEB-MTORC1 signaling and the suppression of autophagy in obesity and metabolic syndrome.