Single-nucleotide variations in the genes encoding the mitochondrial Hsp60/Hsp10 chaperone system and their disease-causing potential

Chaperonin: Co-chaperonin Interactions

Co-chaperonins function together with chaperonins to mediate ATP-dependent protein folding in a variety of cellular compartments. Chaperonins are evolutionarily conserved and form two distinct classes, namely, group I and group II chaperonins. GroEL and its co-chaperonin GroES form part of group I and are the archetypal members of this family of protein folding machines. The unique mechanism used by GroEL and GroES to drive protein folding is embedded in the complex architecture of double-ringed complexes, forming two central chambers that undergo conformational rearrangements that enable protein folding to occur. GroES forms a lid over the chamber and in doing so dislodges bound substrate into the chamber, thereby allowing non-native proteins to fold in isolation. GroES also modulates allosteric transitions of GroEL. Group II chaperonins are functionally similar to group I chaperonins but differ in structure and do not require a co-chaperonin. A significant number of bacteria and eukaryotes house multiple chaperonin and co-chaperonin proteins, many of which have acquired additional intracellular and extracellular biological functions. In some instances, co-chaperonins display contrasting functions to those of chaperonins. Human HSP60 (HSPD) continues to play a key role in the pathogenesis of many human diseases, in particular autoimmune diseases and cancer. A greater understanding of the fascinating roles of both intracellular and extracellular Hsp10 on cellular processes will accelerate the development of techniques to treat diseases associated with the chaperonin family.

Identification of Biochemical and Molecular Markers of Early Aging in Childhood Cancer Survivors

Simple Summary

Childhood cancer survivors (CCS) display a higher risk of developing second malignant tumors and chronic diseases compared with aged-matched controls because of chemo/radiotherapy. This early frailty seems associated with accelerated cell aging, a process correlated with altered mitochondrial energy production. Therefore, this work aims to shed light on the mechanisms involved in chemo/radiotherapy-induced early aging, morbidities, and the risk of developing second tumors in CCS through a biochemical and molecular approach. The identification of crucial mechanisms involved in the CCS chemo/radiotherapy-related pathological conditions will allow identifying therapeutic targets to develop appropriate risk-based care and interventions, minimize morbidities, and maximize the quality of life in the cancer survivor population.

Abstract

Survival rates of childhood cancer patients have improved over the past four decades, although cancer treatments increase the risk of developing chronic diseases typical of aging. Thus, we aimed to identify molecular/metabolic cellular alterations responsible for early aging in childhood cancer survivors (CCS). Biochemical, proteomic, and molecular biology analyses were conducted on mononuclear cells (MNCs) isolated from peripheral blood of 196 CCS, the results being compared with those obtained on MNCs of 154 healthy subjects. CCS-MNCs showed inefficient oxidative phosphorylation associated with low energy status, and increased lipid peroxidation and lactate fermentation compared with age-matched normal controls. According to a mathematical model based on biochemical parameters, CCS-MNCs showed significantly higher metabolic ages than their real ages. The dysfunctional metabolism of CCS-MNCs is associated with lower expression levels of genes and proteins involved in mitochondrial biogenesis and metabolism regulation, such as CLUH, PGC1-alpha, and SIRT6 in CCS, not observed in the age-matched healthy or elderly subjects. In conclusion, our study identified some biochemical and molecular alterations possibly contributing to the pathophysiology of aging and metabolic deficiencies in CCS. These results identify new targets for pharmacological interventions to restore mitochondrial function, slowing down the aging-associated pathologies in CCS.

Complex Destabilization in the Mitochondrial Chaperonin Hsp60 Leads to Disease

Several neurological disorders have been linked to mutations in chaperonin genes and more specifically to the HSPD1 gene. In humans, HSPD1 encodes the mitochondrial Heat Shock Protein 60 (mtHsp60) chaperonin, which carries out essential protein folding reactions that help maintain mitochondrial and cellular homeostasis. It functions as a macromolecular complex that provides client proteins an environment that favors proper folding in an ATP-dependent manner. It has been established that mtHsp60 plays a crucial role in the proper folding of mitochondrial proteins involved in ATP producing pathways. Recently, various single-point mutations in the mtHsp60 encoding gene have been directly linked to neuropathies and paraplegias. Individuals who harbor mtHsp60 mutations that negatively impact its folding ability display phenotypes with highly compromised muscle and neuron cells. Carriers of these mutations usually develop neuropathies and paraplegias at different stages of their lives mainly characterized by leg stiffness and weakness as well as degeneration of spinal cord nerves. These phenotypes are likely due to hindered energy producing pathways involved in cellular respiration resulting in ATP deprived cells. Although the complete protein folding mechanism of mtHsp60 is not well understood, recent work suggests that several of these mutations act by destabilizing the oligomeric stability of mtHsp60. Here, we discuss recent studies that highlight key aspects of the mtHsp60 mechanism with a focus on some of the known disease-causing point mutations, D29G and V98I, and their effect on the protein folding reaction cycle.

Protein trapping leads to altered synaptic proteostasis in synucleinopathies

Parkinson's disease (PD) is associated with the accumulation of alpha-synuclein (aSyn) in intracellular inclusions known as Lewy bodies and Lewy neurites. Under physiological conditions, aSyn is found at the presynaptic terminal and exists in a dynamic equilibrium between soluble, membrane-associated and aggregated forms. Emerging evidence suggests that, under pathological conditions, aSyn begins to accumulate and acquire a toxic function at the synapse, impairing their normal function and connectivity. However, the precise molecular mechanisms linking aSyn accumulation and synaptic dysfunction are still elusive. Here, we provide an overview of our current findings and discuss the hypothesis that certain aSyn aggregates may interact with proteins with whom aSyn normally does not interact with, thereby trapping them and preventing them from performing their normal functions in the cell. We posit that such abnormal interactions start to occur during the prodromal stages of PD, eventually resulting in the overt manifestation of clinical features. Therefore, understanding the nature and behaviour of toxic aSyn species and their contribution to aSyn-mediated toxicity is crucial for the development of therapeutic strategies capable of modifying disease progression in PD and other synucleinopathies.

LIFE BEYOND LIFE - An Easy Way to Derive Lung Fibroblasts from Cadavers

Several protocols have illustrated the possibility of deriving cells, such as fibroblasts, from different organs. These techniques generally concern organs sampled from living persons, but have already been described for cadavers, especially concerning the skin and tendons. We present, for the first time, an easy way to derive pulmonary fibroblasts from a lung tissue sampled from a cadaver and directly culture plated. The fibroblast output was checked daily. We obtained lung fibroblasts from 3 (60%) cadavers and 2 (100%) living persons. The fibroblast output took about 3 days for cells from living persons and took up to 39 days for those from cadavers. We did not clearly identify any parameters that could explain these differences. Nevertheless, these derived cells had the same features as the source cells, especially in terms of morphology and proliferation, and could potentially be used in different research domains such as forensic or regeneration medicine.

Disease-Associated Mutations in the HSPD1 Gene Encoding the Large Subunit of the Mitochondrial HSP60/HSP10 Chaperonin Complex

Heat shock protein 60 (HSP60) forms together with heat shock protein 10 (HSP10) double-barrel chaperonin complexes that are essential for folding to the native state of proteins in the mitochondrial matrix space. Two extremely rare monogenic disorders have been described that are caused by missense mutations in the HSPD1 gene that encodes the HSP60 subunit of the HSP60/HSP10 chaperonin complex. Investigations of the molecular mechanisms underlying these disorders have revealed that different degrees of reduced HSP60 function produce distinct neurological phenotypes. While mutations with deleterious or strong dominant negative effects are not compatible with life, HSPD1 gene variations found in the human population impair HSP60 function and depending on the mechanism and degree of HSP60 dys- and mal-function cause different phenotypes. We here summarize the knowledge on the effects of disturbances of the function of the HSP60/HSP10 chaperonin complex by disease-associated mutations.

The TREM2-DAP12 signaling pathway in Nasu-Hakola disease: a molecular genetics perspective

Nasu–Hakola disease or polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL) is a rare recessively inherited disease that is associated with early dementia and bone cysts with fractures. Here, we review the genetic causes of PLOSL with loss-of-function mutations or deletions in one of two genes, TYROBP and TREM2, encoding for two proteins DNAX-activating protein 12 (DAP12) and triggering receptor expressed on myeloid cells-2 (TREM2). TREM2 and DAP12 form an immunoreceptor signaling complex that mediates myeloid cell, including microglia and osteoclasts, development, activation, and function. Functionally, TREM2-DAP12 mediates osteoclast multi-nucleation, migration, and resorption. In microglia, TREM2-DAP12 participates in recognition and apoptosis of neuronal debris and amyloid deposits. Review of the complex immunoregulatory roles of TREM2-DAP12 in the innate immune system, where it can both promote and inhibit pro-inflammatory responses, is given. Little is known about the function of TREM2-DAP12 in normal brain homeostasis or in pathological central nervous system diseases. Based on the state of the field, genetic testing now aids in diagnosis of PLOSL, but therapeutics and interventions are still under development.

Chaperonin-co-chaperonin interactions

Co-chaperonins function together with chaperonins to mediate ATP-dependant protein folding in a variety of cellular compartments. GroEL and its co-chaperonin GroES are the only essential chaperones in Escherichia coli and are the archetypal members of this family of protein folding machines. The unique mechanism used by GroEL and GroES to drive protein folding is embedded in the complex architecture of double-ringed complexes, forming two central chambers that undergo structural rearrangements as part of the folding mechanism. GroES forms a lid over the chamber, and in doing so dislodges bound substrate into the chamber, thereby allowing non-native proteins to fold in isolation. GroES also modulates allosteric transitions of GroEL. A significant number of bacteria and eukaryotes house multiple chaperonin and co-chaperonin proteins, many of which have acquired additional intracellular and extracellular biological functions. In some instances co-chaperonins display contrasting functions to those of chaperonins. Human Hsp60 continues to play a key role in the pathogenesis of many human diseases, in particular autoimmune diseases and cancer. A greater understanding of the fascinating roles of both intracellular and extracellular Hsp10, in addition to its role as a co-chaperonin, on cellular processes will accelerate the development of techniques to treat diseases associated with the chaperonin family.

Mutation and clinical characteristics of autosomal-dominant hereditary spastic paraplegias in China

BACKGROUND

Hereditary spastic paraplegias constitute a heterogeneous group of inherited neurodegenerative disorders. To date, there has been no systematic mutation and clinical analysis for a large group of autosomal-dominant hereditary spastic paraplegias in China.

OBJECTIVE

The purpose of this study was to investigate the mutation frequencies and the clinical phenotypes of Chinese spastic paraplegia patients.

METHODS

Direct sequencing and a multiplex ligation-dependent probe amplification assay were applied to detect the mutations of SPAST and ATL1 in 54 autosomal-dominant hereditary spastic paraplegia probands and 66 isolated cases. Next, mutations in NIPA1, KIF5A, REEP1 and SLC33A1 were detected in the negative patients. Subsets of spastic paraplegia patients were genotyped for the modifying variants. Further, detailed clinical data regarding the genetically diagnosed families were analysed.

RESULTS

Altogether, 27 families were diagnosed as SPG4, 3 as SPG3A and 1 as SPG6. No mutations in KIF5A, REEP1 or SLC33A1 were found; 9 SPAST mutations were novel. There was no p.S44L or p.P45Q variant in SPAST and no p.G563A variant in HSPD1 in either the 120 spastic paraplegia patients or the 500 controls. There was a remarkable clinical difference between the SPG4 and non-SPG4 patients and even between genders among the SPG4 patients. Non-penetrance and remarkable gender difference were observed in some SPG4 and SPG3A families.

CONCLUSIONS

Our data confirm that hereditary spastic paraplegias in China represent a heterogeneous group of genetic neurodegenerative disorders in autosomal-dominant and apparently sporadic forms. Novel genotype-phenotype correlations were established. © 2014 S. Karger AG, Basel.

Characteristics of human infant primary fibroblast cultures from Achilles tendons removed post-mortem

Primary cell cultures were investigated as a tool for molecular diagnostics in a forensic setting. Fibroblast cultures had been established from human Achilles tendon resected at autopsies, from cases of sudden infant death syndrome and control infants who died in traumatic events (n=41). After isolation of primary cultures cells were stored at -135°C, and re-established up to 15 years later for experimental intervention. Growth characteristics in cultures were evaluated in relation to the age of the donor, the post mortem interval before sampling, and the storage interval of cells before entry into the study. High interpersonal variation in growth rates and cell doubling time was seen, but no statistically significant differences were found with increasing age of the donor (mean 19 weeks), length of post-mortem interval prior to sampling (6-100 h), or increase in years of storage. Fibroblast cultures established from post-mortem tissue are renewable sources of biological material; they can be the foundation for genetic, metabolic and other functional studies and thus constitute a valuable tool for molecular and pathophysiological investigations in biomedical and forensic sciences.

Heat stress and sudden infant death syndrome--stress gene expression after exposure to moderate heat stress

The aim of the present study was to investigate stress gene expression in cultured primary fibroblasts established from Achilles tendons collected during autopsies from sudden infant death syndrome (SIDS) cases, and age-matched controls (infants dying in a traumatic event). Expression of 4 stress responsive genes, HSPA1B, HSPD1, HMOX1, and SOD2, was studied by quantitative reverse transcriptase PCR analysis of RNA purified from cells cultured under standard or various thermal stress conditions. The expression of all 4 genes was highly influenced by thermal stress in both SIDS and control cells. High interpersonal variance found in the SIDS group indicated that they represented a more heterogeneous group than controls. The SIDS group responded to thermal stress with a higher expression of the HSPA1B and HSPD1 genes compared to the control group, whereas no significant difference was observed in the expression of SOD2 and HMOX1 between the two groups. The differences were related to the heat shock treatment as none of the genes were expressed significantly different in SIDS at base levels at 37 °C. SOD2 and HMOX1 were up regulated in both groups, for SOD2 though the expression was lower in SIDS at all time points measured, and may be less related to heat stress. Being found dead in the prone position (a known risk factor for SIDS) was related to a lower HSPA1B up-regulation in SIDS compared to SIDS found on their side or back. The study demonstrates the potential usefulness of gene expression studies using cultured fibroblasts established from deceased individuals as a tool for molecular and pathological investigations in forensic and biomedical sciences.

Functional single-nucleotide variant of HSPD1 in sudden infant death syndrome

BACKGROUND

An insufficient stress response due to a genetically impaired heat shock protein (Hsp) could play a role in the pathogenesis in a subgroup of sudden infant death syndrome (SIDS) cases. Herein, we are the first to investigate whether a functionally impairing and thus pathogenic variant of the gene for Hsp60, encoded by HSPD1 (rs72466451), is correlated with the occurrence of SIDS.

METHODS

In a case-control study of a series of 133 cases of SIDS and 192 gender-matched German Caucasian control cases, the occurrence and distribution of the HSPD1 single-nucleotide variant (SNV) was analyzed using SNV genotyping by minisequencing.

RESULTS

The results show significantly increased frequency of the pathogenic variant of the HSPD1 SNV in a subgroup (4.5%) of SIDS cases.

CONCLUSION

The results suggest that the pathogenic variant of rs72466451 may play a role in a subgroup of SIDS cases with impaired Hsp60-mediated stress response.

Proteomic changes in HEK-293 cells induced by hepatitis delta virus replication

Hepatitis delta virus (HDV) infection greatly increases the risk of hepatocellular carcinoma in hepatitis B virus chronically infected patients. HDV is highly dependent on host factors for accomplishment of the replication cycle. However, these factors are largely unknown and the mechanisms involved in the pathogenicity of the virus still remain elusive. Here, we made use of the HEK-293 cell line, which was engineered in order to mimic HDV replication. Five different proteomes were analyzed and compared using a MS-based quantitative proteomics approach by (18)O/(16)O stable isotope labeling. About 3000 proteins were quantified and 89 found to be differentially expressed as a consequence HDV RNA replication. The down-regulation of p53 , HSPE, and ELAV as well as the up-regulation of Transportin 1 , EIF3D, and Cofilin 1 were validated by Western blot. A systems biology approach was additionally used to analyze altered pathways and networks. The G2/M DNA damage checkpoint and pyruvate metabolism were among the most affected pathways, and Cancer was the most likely disease associated to HDV replication. Western blot analysis allowed identifying 14-3-3 σ interactor as down-regulated protein acting in the G2/M cell cycle control checkpoint. This evidence supports deregulation of G2/M checkpoint as a possible mechanism involved in the promotion of HDV associated hepatocellular carcinoma.

BIOLOGICAL SIGNIFICANCE

This manuscript provides a description of changes observed in the cellular proteome that arise as result of expression of the hepatitis delta virus (HDV) antigen as well as virus genome replication. Using a systems biology approach cancer was found to be the most probable disease associated with HDV replication. Additionally, results show that HDV alters the regulation of G2/M cell cycle control checkpoint. Taken together, our data provide new insights into probable mechanisms associated with the increased incidence of hepatocellular carcinoma observed in HDV infected patients.

Gene variants predisposing to SIDS: current knowledge

Genetic risk factors play a role in sudden unexpected infant death; either as a cause of death, such as in cases with medium-chain acyl-coenzyme A dehydrogenase deficiency and cardiac arrest due to long QT syndrome, or as predisposing factors for sudden infant death syndrome (SIDS). Most likely genetic predisposition to SIDS represent a polygenic inheritance pattern leading to sudden death when combined with other risk factors, such as a vulnerable developmental stage of the central nervous system and/or the immune system, in addition to environmental risk factors, such as a common cold or prone sleeping position. Genes involved in the regulation of the immune system, cardiac function, the serotonergic network and brain function and development have so far emerged as the most important with respect to SIDS. The purpose of the present paper is to survey current knowledge on SIDS and possible genetic contributions.

Sequence variants in SPAST, SPG3A and HSPD1 in hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a group of clinically and genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and weakness in the lower limbs. The most common forms of autosomal dominant HSP, SPG4 and SPG3, are caused by sequence variants in the SPAST and SPG3A genes, respectively. The pathogenic variants are scattered all over these genes and many variants are unique to a specific family. The phenotype in SPG4 patients can be modified by a variant in SPAST (p.Ser44Leu) and recently, a variant in HSPD1, the gene underlying SPG13, was reported as a second genetic modifier in SPG4 patients. In this study HSP patients were screened for variants in SPG3A, SPAST and HSPD1 in order to identify disease causing variations. SPAST was sequenced in all patients whereas subsets were sequenced in HSPD1 and in selected exons of SPG3A. SPG4 patients and their HSP relatives were genotyped for the modifying variant in HSPD1. We report six new sequence variants in SPAST including a fourth non synonymous sequence variant in exon 1 and two synonymous changes of which one has been found in a HSP patient previously, but never in controls. Of the novel variants in SPAST four were interpreted as disease causing. In addition one new disease causing sequence variant and one non pathogenic non synonymous variant were found in SPG3A. In HSPD1 we identified a sporadic patient homozygote for the potential modifying variation. The effect of the modifying HSPD1 variation was not supported by identification in one SPG4 family.

Mitochondrial hsp60 chaperonopathy causes an autosomal-recessive neurodegenerative disorder linked to brain hypomyelination and leukodystrophy

Hypomyelinating leukodystrophies (HMLs) are disorders involving aberrant myelin formation. The prototype of primary HMLs is the X-linked Pelizaeus-Merzbacher disease (PMD) caused by mutations in PLP1. Recently, homozygous mutations in GJA12 encoding connexin 47 were found in patients with autosomal-recessive Pelizaeus-Merzbacher-like disease (PMLD). However, many patients of both genders with PMLD carry neither PLP1 nor GJA12 mutations. We report a consanguineous Israeli Bedouin kindred with clinical and radiological findings compatible with PMLD, in which linkage to PLP1 and GJA12 was excluded. Using homozygosity mapping and mutation analysis, we have identified a homozygous missense mutation (D29G) not previously described in HSPD1, encoding the mitochondrial heat-shock protein 60 (Hsp60) in all affected individuals. The D29G mutation completely segregates with the disease-associated phenotype. The pathogenic effect of D29G on Hsp60-chaperonin activity was verified by an in vivo E. coli complementation assay, which demonstrated compromised ability of the D29G-Hsp60 mutant protein to support E. coli survival, especially at high temperatures. The disorder, which we have termed MitCHAP-60 disease, can be distinguished from spastic paraplegia 13 (SPG13), another Hsp60-associated autosomal-dominant neurodegenerative disorder, by its autosomal-recessive inheritance pattern, as well as by its early-onset, profound cerebral involvement and lethality. Our findings suggest that Hsp60 defects can cause neurodegenerative pathologies of varying severity, not previously suspected on the basis of the SPG13 phenotype. These findings should help to clarify the important role of Hsp60 in myelinogenesis and neurodegeneration.

Sudden infant death syndrome: another year of new hope but no cure

PURPOSE OF REVIEW

Sudden infant death syndrome has inspired increasingly sophisticated studies at a time when rates are declining because of the Back-to-Sleep campaign, but ethnic disparities are widening. This review evaluates and discusses original, recent research in this area.

RECENT FINDINGS

The epidemiology of sudden infant death syndrome was evaluated, corroborating known risk factors and identifying new risk factors such as socioeconomic depression and air pollution. Deficits in our understanding of risk factors for this syndrome persist, suggesting a need for ethnicity-specific education, especially among the underserved. Both autopsy and genetic testing were found to improve diagnostic accuracy or identify other causes of death (e.g. long Q-T syndrome). Debate persists over counseling regarding pacifiers and co-sleeping within the context of breastfeeding. Support was found for a relationship between sudden infant death syndrome and autonomic dysregulation via the serotonergic pathway, but more research is needed.

SUMMARY

The cause of sudden infant death syndrome remains elusive. Recent studies, however, suggest that improved culturally sensitive educational programs, increased diagnostic specificity, and further clarification of the link between genetics and developmental stage might further decrease the number of infants lost to this devastating disease and elucidate the mechanism(s) responsible for this syndrome.