2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency is caused by mutations in the HADH2 gene

SPAG7 deletion causes intrauterine growth restriction, resulting in adulthood obesity and metabolic dysfunction

From a forward mutagenetic screen to discover mutations associated with obesity, we identified mutations in the Spag7 gene linked to metabolic dysfunction in mice. Here, we show that SPAG7 KO mice are born smaller and develop obesity and glucose intolerance in adulthood. This obesity does not stem from hyperphagia, but a decrease in energy expenditure. The KO animals also display reduced exercise tolerance and muscle function due to impaired mitochondrial function. Furthermore, SPAG7-deficiency in developing embryos leads to intrauterine growth restriction, brought on by placental insufficiency, likely due to abnormal development of the placental junctional zone. This insufficiency leads to loss of SPAG7-deficient fetuses in utero and reduced birth weights of those that survive. We hypothesize that a 'thrifty phenotype' is ingrained in SPAG7 KO animals during development that leads to adult obesity. Collectively, these results indicate that SPAG7 is essential for embryonic development and energy homeostasis later in life.

Discovery, structure, mechanisms, and evolution of protein-only RNase P enzymes

The endoribonuclease RNase P is responsible for tRNA 5' maturation in all domains of life. A unique feature of RNase P is the variety of enzyme architectures, ranging from dual- to multi-subunit ribonucleoprotein forms with catalytic RNA subunits to protein-only enzymes, the latter occurring as single- or multi-subunit forms or homo-oligomeric assemblies. The protein-only enzymes evolved twice: a eukaryal protein-only RNase P termed PRORP and a bacterial/archaeal variant termed homolog of Aquifex RNase P (HARP); the latter replaced the RNA-based enzyme in a small group of thermophilic bacteria but otherwise coexists with the ribonucleoprotein enzyme in a few other bacteria as well as in those archaea that also encode a HARP. Here we summarize the history of the discovery of protein-only RNase P enzymes and review the state of knowledge on structure and function of bacterial HARPs and eukaryal PRORPs, including human mitochondrial RNase P as a paradigm of multi-subunit PRORPs. We also describe the phylogenetic distribution and evolution of PRORPs, as well as possible reasons for the spread of PRORPs in the eukaryal tree and for the recruitment of two additional protein subunits to metazoan mitochondrial PRORP. We outline potential applications of PRORPs in plant biotechnology and address diseases associated with mutations in human mitochondrial RNase P genes. Finally, we consider possible causes underlying the displacement of the ancient RNA enzyme by a protein-only enzyme in a small group of bacteria.

Involvement of Type 10 17β-Hydroxysteroid Dehydrogenase in the Pathogenesis of Infantile Neurodegeneration and Alzheimer's Disease

Type 10 17β-hydroxysteroid dehydrogenase (17β-HSD10) is the HSD17B10 gene product playing an appreciable role in cognitive functions. It is the main hub of exercise-upregulated mitochondrial proteins and is involved in a variety of metabolic pathways including neurosteroid metabolism to regulate allopregnanolone homeostasis. Deacetylation of 17β-HSD10 by sirtuins helps regulate its catalytic activities. 17β-HSD10 may also play a critical role in the control of mitochondrial structure, morphology and dynamics by acting as a member of the Parkin/PINK1 pathway, and by binding to cyclophilin D to open mitochondrial permeability pore. 17β-HSD10 also serves as a component of RNase P necessary for mitochondrial tRNA maturation. This dehydrogenase can bind with the Aβ peptide thereby enhancing neurotoxicity to brain cells. Even in the absence of Aβ, its quantitative and qualitative variations can result in neurodegeneration. Since elevated levels of 17β-HSD10 were found in brain cells of Alzheimer's disease (AD) patients and mouse AD models, it is considered to be a key factor in AD pathogenesis. Since data underlying Aβ-binding-alcohol dehydrogenase (ABAD) were not secured from reported experiments, ABAD appears to be a fabricated alternative term for the HSD17B10 gene product. Results of this study would encourage researchers to solve the question why elevated levels of 17β-HSD10 are present in brains of AD patients and mouse AD models. Searching specific inhibitors of 17β-HSD10 may find candidates to reduce senile neurodegeneration and open new approaches for the treatment of AD.

Infantile Neurodegeneration Results from Mutants of 17β-Hydroxysteroid Dehydrogenase Type 10 Rather Than Aβ-Binding Alcohol Dehydrogenase

Type 10 17β-hydroxysteroid dehydrogenase (17β-HSD10), a homo-tetrameric multifunctional protein with 1044 residues encoded by the HSD17B10 gene, is necessary for brain cognitive function. Missense mutations result in infantile neurodegeneration, an inborn error in isoleucine metabolism. A 5-methylcytosine hotspot underlying a 388-T transition leads to the HSD10 (p.R130C) mutant to be responsible for approximately half of all cases suffering with this mitochondrial disease. Fewer females suffer with this disease due to X-inactivation. The binding capability of this dehydrogenase to Aβ-peptide may play a role in Alzheimer's disease, but it appears unrelated to infantile neurodegeneration. Research on this enzyme was complicated by reports of a purported Aβ-peptide-binding alcohol dehydrogenase (ABAD), formerly referred to as endoplasmic-reticulum-associated Aβ-binding protein (ERAB). Reports concerning both ABAD and ERAB in the literature reflect features inconsistent with the known functions of 17β-HSD10. It is clarified here that ERAB is reportedly a longer subunit of 17β-HSD10 (262 residues). 17β-HSD10 exhibits L-3-hydroxyacyl-CoA dehydrogenase activity and is thus also referred to in the literature as short-chain 3-hydorxyacyl-CoA dehydrogenase or type II 3-hydorxyacyl-CoA dehydrogenase. However, 17β-HSD10 is not involved in ketone body metabolism, as reported in the literature for ABAD. Reports in the literature referring to ABAD (i.e., 17β-HSD10) as a generalized alcohol dehydrogenase, relying on data underlying ABAD's activities, were found to be unreproducible. Furthermore, the rediscovery of ABAD/ERAB's mitochondrial localization did not cite any published research on 17β-HSD10. Clarification of the purported ABAD/ERAB function derived from these reports on ABAD/ERAB may invigorate this research field and encourage new approaches to the understanding and treatment of HSD17B10-gene-related disorders. We establish here that infantile neurodegeneration is caused by mutants of 17β-HSD10 but not ABAD, and so we conclude that ABAD represents a misnomer employed in high-impact journals.

3-Hydroxyacyl-CoA and Alcohol Dehydrogenase Activities of Mitochondrial Type 10 17β-Hydroxysteroid Dehydrogenase in Neurodegeneration Study

BACKGROUND

Mitochondrial 17β-hydroxysteroid dehydrogenase type 10 (17β-HSD10) is necessary for brain cognitive function, but its studies were confounded by reports of Aβ-peptide binding alcohol dehydrogenase (ABAD), formerly endoplasmic reticulum-associated Aβ-peptide binding protein (ERAB), for two decades so long as ABAD serves as the alternative term of 17β-HSD10.

OBJECTIVE

To determine whether those ABAD reports are true or false, even if they were published in prestigious journals.

METHODS

6xHis-tagged 17β-HSD10 was prepared and characterized by well-established experimental procedures.

RESULTS

The N-terminal 6xHis tag did not significantly interfere with the dehydrogenase activities of 17β-HSD10, but the kinetic constants of its 3-hydroxyacyl-CoA dehydrogenase activity are drastically distinct from those of ABAD, and it was not involved in ketone body metabolism as previously reported for ABAD. Furthermore, it was impossible to measure its generalized alcohol dehydrogenase activities underlying the concept of ABAD because the experimental procedures described in ABAD reports violated basic chemical and/or biochemical principles. More incredibly, both authors and journals had not yet agreed to make any corrigenda of ABAD reports.

CONCLUSION

Brain 17β-HSD10 plays a key role in neurosteroid metabolism and further studies in this area may lead to potential treatments of neurodegeneration including AD.

Bi-allelic variants in the mitochondrial RNase P subunit PRORP cause mitochondrial tRNA processing defects and pleiotropic multisystem presentations

Human mitochondrial RNase P (mt-RNase P) is responsible for 5′ end processing of mitochondrial precursor tRNAs, a vital step in mitochondrial RNA maturation, and is comprised of three protein subunits: TRMT10C, SDR5C1 (HSD10), and PRORP. Pathogenic variants in TRMT10C and SDR5C1 are associated with distinct recessive or x-linked infantile onset disorders, resulting from defects in mitochondrial RNA processing. We report four unrelated families with multisystem disease associated with bi-allelic variants in PRORP, the metallonuclease subunit of mt-RNase P. Affected individuals presented with variable phenotypes comprising sensorineural hearing loss, primary ovarian insufficiency, developmental delay, and brain white matter changes. Fibroblasts from affected individuals in two families demonstrated decreased steady state levels of PRORP, an accumulation of unprocessed mitochondrial transcripts, and decreased steady state levels of mitochondrial-encoded proteins, which were rescued by introduction of the wild-type PRORP cDNA. In mt-tRNA processing assays performed with recombinant mt-RNase P proteins, the disease-associated variants resulted in diminished mitochondrial tRNA processing. Identification of disease-causing variants in PRORP indicates that pathogenic variants in all three subunits of mt-RNase P can cause mitochondrial dysfunction, each with distinct pleiotropic clinical presentations.

HSD10 disease in a female: A case report and review of literature

HSD10 disease is a rare X-linked mitochondrial disorder caused by pathogenic variants in the HSD17B10 gene. The phenotype results from impaired 17β-hydroxysteroid dehydrogenase 10 (17β-HSD10) protein structure and function. HSD10 is a multifunctional protein involved in enzymatic degradation of isoleucine and branched-chain fatty acids, the metabolism of sex hormones and neurosteroids, as well as in regulating mitochondrial RNA maturation. HSD10 disease is characterised by progressive neurologic impairment. Disease onset is varied and includes neonatal-onset, infantile-onset and late-onset in males. Females can also be affected. Our index case is a 45-month-old female, who initially presented at 11 months of age with global developmental delay. She subsequently began to lose previously acquired cognitive and motor skills starting around 29 months of age. Brain MRI showed abnormalities in the basal ganglia indicative of possible mitochondrial disease. Urine organic acid analysis revealed elevations of 2-methyl-3-hydroxybutyric acid and tiglyglycine. HSD17B10 gene sequencing revealed a likely pathogenic variant, NM_001037811.2:c.439C>T (p.Arg147Cys) inherited from her mother, expected to be causative of HSD10 disease. Her X-chromosome inactivation study is consistent with a skewed X-inactivation pattern. We report a female patient with HSD10 disease caused by a missense pathogenic variant, Arg147Cys in the HSD17B10 gene. The patient is the fifth severely affected female with this disease. This case adds to the small number of known affected families with this highly variable disease in the literature. These findings support the possibility of X-inactivation patterns influencing the penetrance of HSD10 disease in females.

Deacetylation of HSD17B10 by SIRT3 regulates cell growth and cell resistance under oxidative and starvation stresses

17-beta-hydroxysteroid dehydrogenase 10 (HSD17B10) plays an important role in mitochondrial fatty acid metabolism and is also involved in mitochondrial tRNA maturation. HSD17B10 missense mutations cause HSD10 mitochondrial disease (HSD10MD). HSD17B10 with mutations identified from cases of HSD10MD show loss of function in dehydrogenase activity and mitochondrial tRNA maturation, resulting in mitochondrial dysfunction. It has also been implicated to play roles in the development of Alzheimer disease (AD) and tumorigenesis. Here, we found that HSD17B10 is a new substrate of NAD-dependent deacetylase Sirtuin 3 (SIRT3). HSD17B10 is acetylated at lysine residues K79, K99 and K105 by the acetyltransferase CBP, and the acetylation is reversed by SIRT3. HSD17B10 acetylation regulates its enzymatic activity and the formation of mitochondrial RNase P. Furthermore, HSD17B10 acetylation regulates the intracellular functions, affecting cell growth and cell resistance in response to stresses. Our results demonstrated that acetylation is an important regulation mechanism for HSD17B10 and may provide insight into interrupting the development of AD.

Friend or enemy? Review of 17β-HSD10 and its role in human health or disease

17β-hydroxysteroid dehydrogenase (17β-HSD10) is a multifunctional human enzyme with important roles both as a structural component and also as a catalyst of many metabolic pathways. This mitochondrial enzyme has important functions in the metabolism, development and aging of the neural system, where it is involved in the homeostasis of neurosteroids, especially in regard to estradiol, changes in which make it an essential part of neurodegenerative pathology. These roles therefore, indicate that 17β-HSD10 may be a possible druggable target for neurodegenerative diseases including Alzheimer's disease (AD), and in hormone-dependent cancer. The objective of this review was to provide a summary about physiological functions and pathological roles of 17β-HSD10 and the modulators of its activity.

2-methylacetoacetyl-coenzyme A thiolase (beta-ketothiolase) deficiency: one disease - two pathways

Background

2-methylacetoacetyl-coenzyme A thiolase deficiency (MATD; deficiency of mitochondrial acetoacetyl-coenzyme A thiolase T2/ “beta-ketothiolase”) is an autosomal recessive disorder of ketone body utilization and isoleucine degradation due to mutations in ACAT1.

Methods

We performed a systematic literature search for all available clinical descriptions of patients with MATD. Two hundred forty-four patients were identified and included in this analysis. Clinical course and biochemical data are presented and discussed.

Results

For 89.6% of patients at least one acute metabolic decompensation was reported. Age at first symptoms ranged from 2 days to 8 years (median 12 months). More than 82% of patients presented in the first 2 years of life, while manifestation in the neonatal period was the exception (3.4%). 77.0% (157 of 204 patients) of patients showed normal psychomotor development without neurologic abnormalities.

Conclusion

This comprehensive data analysis provides a systematic overview on all cases with MATD identified in the literature. It demonstrates that MATD is a rather benign disorder with often favourable outcome, when compared with many other organic acidurias.

HSD10 mitochondrial disease: p.Leu122Val variant, mild clinical phenotype, and founder effect in French-Canadian patients from Quebec

BACKGROUND

HSD10 mitochondrial disease (HSD10MD), originally described as a deficiency of 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD), is a rare X-linked disorder of a moonlighting protein encoded by the HSD17B10. The diagnosis is usually first suspected on finding elevated isoleucine degradation metabolites in urine, reflecting decreased MHBD activity. However, it is now known that clinical disease pathogenesis reflects other independent functions of the HSD10 protein; particularly its essential role in mitochondrial transcript processing and tRNA maturation. The classical phenotype of HSD10MD in affected males is an infantile-onset progressive neurodegenerative disorder associated with severe mitochondrial dysfunction.

PATIENTS, METHODS, AND RESULTS

In four unrelated families, we identified index patients with MHBD deficiency, which implied a diagnosis of HSD10MD. Each index patient was independently investigated because of neurological or developmental concerns. All had persistent elevations of urinary 2-methyl-3-hydroxybutyric acid and tiglylglycine. Analysis of HSD17B10 identified a single missense variant, c.364C>G, p.Leu122Val, in each case. This rare variant (1/183336 alleles in gnomAD) was previously reported in one Dutch patient and was described as pathogenic. The geographic origins of our families and results of haplotype analysis together provide evidence of a founder effect for this variant in Quebec. Notably, we identified an asymptomatic hemizygous adult male in one family, while a second independent genetic disorder contributed substantially to the clinical phenotypes observed in probands from two other families.

CONCLUSION

The phenotype associated with p.Leu122Val in HSD17B10 currently appears to be attenuated and nonprogressive. This report widens the spectrum of phenotypic severity of HSD10MD and contributes to genotype-phenotype correlation. At present, we consider p.Leu122Val a "variant of uncertain significance." Nonetheless, careful follow-up of our patients remains advisable, to assess long-term clinical course and ensure appropriate management. It will also be important to identify other potential patients in our population and to characterize their phenotype.

17B-hydroxysteroid dehydrogenases as acyl thioester metabolizing enzymes

17β-Hydroxysteroid dehydrogenases (HSD17B) catalyze the oxidation/reduction of 17β-hydroxy/keto group in position C17 in C18- and C19 steroids. Most HSD17Bs are also catalytically active with substrates other than steroids. A subset of these enzymes is able to process thioesters of carboxylic acids. This group of enzymes includes HSD17B4, HSD17B8, HSD17B10 and HSD17B12, which execute reactions in intermediary metabolism, participating in peroxisomal β-oxidation of fatty acids, mitochondrial oxidation of 3R-hydroxyacyl-groups, breakdown of isoleucine and fatty acid chain elongation in endoplasmic reticulum. Divergent substrate acceptance capabilities exemplify acquirement of catalytic site adaptiveness during evolution. As an additional common feature these HSD17Bs are multifunctional enzymes that arose either via gene fusions (HSD17B4) or are incorporated as subunits into multifunctional protein complexes (HSD17B8 and HSD17B10). Crystal structures of HSD17B4, HSD17B8 and HSD17B10 give insight into their structure-function relationships. Thus far, deficiencies of HSD17B4 and HSD17B10 have been assigned to inborn errors in humans, underlining their significance as enzymes of metabolism.

Subcellular localization and membrane topology of 17β-hydroxysteroid dehydrogenases

The 17β-hydroxysteroid dehydrogenases (17β-HSDs) comprise enzymes initially identified by their ability to interconvert active and inactive forms of sex steroids, a vital process for the tissue-specific control of estrogen and androgen balance. However, most 17β-HSDs have now been shown to accept substrates other than sex steroids, including bile acids, retinoids and fatty acids, thereby playing unanticipated roles in cell physiology. This functional divergence is often reflected by their different subcellular localization, with 17β-HSDs found in the cytosol, peroxisome, mitochondria, endoplasmic reticulum and in lipid droplets. Moreover, a subset of 17β-HSDs are integral membrane proteins, with their specific topology dictating the cellular compartment in which they exert their enzymatic activity. Here, we summarize the present knowledge on the subcellular localization and membrane topology of the 17β-HSD enzymes and discuss the correlation with their biological functions.

Neurocognitive assessments and long-term outcome in an adult with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency

Background

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency (MHBDD) is a rare X-linked disorder associated with the accumulation of 2-methyl-3-hydroxybutyric acid in body fluids as a consequence of a disruption in isoleucine metabolism. The clinical presentation is heterogeneous, including a neurodegenerative course with retinopathy and cardiomyopathy leading to death in early childhood and a slowly progressive disease associated with learning disability and survival into adulthood. The condition is often diagnosed in childhood.

Results

This paper outlines the long-term neurocognitive outcomes in a 38-year old man with MHBDD. Several psychometric tests were used to assess his cognitive ability and adaptive functioning in childhood during an acute illness and in adulthood when the patient showed deterioration in the ability to walk or speak.

Conclusions

There is an increasing demand for an accurate and objective measure of cognitive functioning that can be used to follow the natural progression of MHBDD. Psychological assessment may enable the identification of organic problems. The application and interpretation of psychometric tests used in children may vary from those used in adults.

Discovery and Engineering of Pathways for Production of α-Branched Organic Acids

Cell-based synthesis offers many opportunities for preparing small molecules from simple renewable carbon sources by telescoping multiple reactions into a single fermentation step. One challenge in this area is the development of enzymatic carbon-carbon bond forming cycles that enable a modular disconnection of a target structure into cellular building blocks. In this regard, synthetic pathways based on thiolase enzymes to catalyze the initial carbon-carbon bond forming step between acyl coenzyme A (CoA) substrates offer a versatile route for biological synthesis, but the substrate diversity of such pathways is currently limited. In this report, we describe the identification and biochemical characterization of a thiolase-ketoreductase pair involved in production of branched acids in the roundworm, Ascaris suum, that demonstrates selectivity for forming products with an α-methyl branch using a propionyl-CoA extender unit. Engineering synthetic pathways for production of α-methyl acids in Escherichia coli using these enzymes allows the construction of microbial strains that produce either chiral 2-methyl-3-hydroxy acids (1.1 ± 0.2 g L^-1) or branched enoic acids (1.12 ± 0.06 g L^-1) in the presence of a dehydratase at 44% and 87% yield of fed propionate, respectively. In vitro characterization along with in vivo analysis indicates that the ketoreductase is the key driver for selectivity, forming predominantly α-branched products even when paired with a thiolase that highly prefers unbranched linear products. Our results expand the utility of thiolase-based pathways and provide biosynthetic access to α-branched compounds as precursors for polymers and other chemicals.

Novel patient missense mutations in the HSD17B10 gene affect dehydrogenase and mitochondrial tRNA modification functions of the encoded protein

MRPP2 (also known as HSD10/SDR5C1) is a multifunctional protein that harbours both catalytic and non-catalytic functions. The protein belongs to the short-chain dehydrogenase/reductases (SDR) family and is involved in the catabolism of isoleucine in vivo and steroid metabolism in vitro. MRPP2 also moonlights in a complex with the MRPP1 (also known as TRMT10C) protein for N1-methylation of purines at position 9 of mitochondrial tRNA, and in a complex with MRPP1 and MRPP3 (also known as PRORP) proteins for 5'-end processing of mitochondrial precursor tRNA. Inherited mutations in the HSD17B10 gene encoding MRPP2 protein lead to a childhood disorder characterised by progressive neurodegeneration, cardiomyopathy or both. Here we report two patients with novel missense mutations in the HSD17B10 gene (c.34G>C and c.526G>A), resulting in the p.V12L and p.V176M substitutions. Val12 and Val176 are highly conserved residues located at different regions of the MRPP2 structure. Recombinant mutant proteins were expressed and characterised biochemically to investigate their effects towards the functions of MRPP2 and associated complexes in vitro. Both mutant proteins showed significant reduction in the dehydrogenase, methyltransferase and tRNA processing activities compared to wildtype, associated with reduced stability for protein with p.V12L, whereas the protein carrying p.V176M showed impaired kinetics and complex formation. This study therefore identified two distinctive molecular mechanisms to explain the biochemical defects for the novel missense patient mutations.

Ocular manifestations in the X-linked intellectual disability syndromes

Intellectual disability (ID), a common neurodevelopmental disorder characterized by limitations of both intellectual functioning and adaptive behavior, affects an estimated 1-2% of children. Genetic causes of ID are often accompanied by recognizable syndromal patterns. The vision apparatus is a sensory extension of the brain, and individuals with intellectual disabilities frequently have coexisting abnormalities of ocular structures and the visual pathway system. About one-third of the X-linked intellectual disability (XLID) syndromes have significant eye or ocular adnexa abnormalities that provide important diagnostic clues. Some XLID syndromes (e.g. Aicardi, cerebrooculogenital, Graham anophthalmia, Lenz, Lowe, MIDAS) are widely known for their characteristic ocular manifestations. Nystagmus, optic atrophy, and strabismus are among the more common, nonspecific, ocular manifestations that contribute to neuro-ophthalmological morbidity. Common dysmorphic oculofacial findings include anophthalmia, microphthalmia, hypertelorism, and abnormalities in the configuration or orientation of the palpebral fissures. Four XLID syndromes with major ocular manifestations (incontinentia pigmenti, Goltz, MIDAS, and Aicardi syndromes) are notable because of male lethality and expression occurring predominantly in females. The majority of the genes associated with XLID and ocular manifestations have now been identified.

Physical Exercise and Brain Mitochondrial Fitness: The Possible Role Against Alzheimer's Disease

Exercise is one of the most effective strategies to maintain a healthy body and mind, with particular beneficial effects of exercise on promoting brain plasticity, increasing cognition and reducing the risk of cognitive decline and dementia in later life. Moreover, the beneficial effects resulting from increased physical activity occur at different levels of cellular organization, mitochondria being preferential target organelles. The relevance of this review article relies on the need to integrate the current knowledge of proposed mechanisms, focus mitochondria, to explain the protective effects of exercise that might underlie neuroplasticity and seeks to synthesize these data in the context of exploring exercise as a feasible intervention to delay cognitive impairment associated with neurodegenerative conditions, particularly Alzheimer disease.

Japanese Male Siblings with 2-Methyl-3-Hydroxybutyryl-CoA Dehydrogenase Deficiency (HSD10 Disease) Without Neurological Regression

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency (HSD10 disease) is a rare X-linked disorder caused by a mutation in the HSD17B10 gene. Fewer than 30 patients with this disorder have been reported worldwide. The classical infantile form of HSD10 disease is characterized by a progressive neurodegenerative course with retinopathy and cardiomyopathy, although HSD10 disease has broad clinical heterogeneity. However, several male patients have not shown neurological regression. Here, we describe two Japanese siblings with HSD10 disease without neurological regression. A 4-year-old boy presented with unconsciousness due to severe hypoglycemia. Laboratory testing on admission showed mild metabolic acidosis and mild hyperammonemia. Urinary organic acid analysis in the acute phase showed elevated excretion of 2-methyl-3-hydroxybutyric acid, tiglylglycine, and ketones. However, 2-methylacetoacetate was not elevated. HSD10 disease was suspected based on urinary organic acid data. The patient had a novel hemizygous c.470C>T (p.A157V) mutation in the HSD17B10 gene. His mother was a heterozygous carrier of this mutation. The patient's older brother also had the c.470C>T (p.A157V) mutation. Neurological development was normal at the time of evaluation. The pilot newborn screening results using tandem mass spectrometry of the proband were reevaluated retrospectively and showed a high C5:1 carnitine level of 0.070 nmol/mL (upper cutoff limit, 0.05 nmol/mL) and a normal C5-OH carnitine level of 0.290 nmol/mL (upper cutoff limit, 1.0 nmol/mL). His affected brother and another patient with the atypical form of HSD10 disease having p.A154T also showed elevated C5:1 but not C5-OH in serum acylcarnitine analysis. Thus, these data suggested that some patients with this disorder may be identified using newborn screening.

Hydroxysteroid 17-Beta Dehydrogenase Type 10 Disease in Siblings

Hydroxysteroid 17-beta dehydrogenase type 10 (HSD10) deficiency (HSD10 disease) is a rare X-linked neurodegenerative condition caused by abnormalities in the HSD17B10 gene. A total of 10 mutations have been reported in the literature since 2000. Described phenotypes include a severe neonatal or progressive infantile form with hypotonia, choreoathetosis, seizures, cardiomyopathy, neurodegeneration, and death, as well as an attenuated form with variable regression. Here we present the second report of a c.194T>C (p.V65A) mutation in two half-brothers with a clinical phenotype characterized by neurodevelopmental delay, choreoathetosis, visual loss, cardiac findings, and behavioral abnormalities, with regressions now noted in the older sibling. Neither has experienced a metabolic crisis. Both of the siblings had normal tandem mass spectroscopy analysis of their newborn screening samples. The older brother's phenotype may be complicated by the presence of a 3q29 microduplication. Diagnosis requires a high index of suspicion, as the characteristic urine organic acid pattern may escape detection. The exact pathogenic mechanism of disease remains to be elucidated, but may involve the non-dehydrogenase functionalities of the HSD10 protein. Our report highlights clinical features of two patients with the less fulminant phenotype associated with a V65A mutation, compares the reported phenotypes to date, and reviews recent findings regarding the potential pathophysiology of this condition.Summary Sentence Hydroxysteroid 17-beta dehydrogenase type 10 (HSD10) disease (HSD10 disease) is a rare X-linked neurodegenerative condition with a variable clinical phenotype; diagnosis requires a high index of suspicion.

Chemoproteomic Strategy to Quantitatively Monitor Transnitrosation Uncovers Functionally Relevant S-Nitrosation Sites on Cathepsin D and HADH2

S-Nitrosoglutathione (GSNO) is an endogenous transnitrosation donor involved in S-nitrosation of a variety of cellular proteins, thereby regulating diverse protein functions. Quantitative proteomic methods are necessary to establish which cysteine residues are most sensitive to GSNO-mediated transnitrosation. Here, a competitive cysteine-reactivity profiling strategy was implemented to quantitatively measure the sensitivity of >600 cysteine residues to transnitrosation by GSNO. This platform identified a subset of cysteine residues with a high propensity for GSNO-mediated transnitrosation. Functional characterization of previously unannotated S-nitrosation sites revealed that S-nitrosation of a cysteine residue distal to the 3-hydroxyacyl-CoA dehydrogenase type 2 (HADH2) active site impaired catalytic activity. Similarly, S-nitrosation of a non-catalytic cysteine residue in the lysosomal aspartyl protease cathepsin D (CTSD) inhibited proteolytic activation. Together, these studies revealed two previously uncharacterized cysteine residues that regulate protein function, and established a chemical-proteomic platform with capabilities to determine substrate specificity of other cellular transnitrosation agents.

Estrogen-mediated regulation of mitochondrial gene expression

Estrogens, in particular 17β-estradiol, are well-known regulators of essential cellular functions; however, discrepancies remain over the mechanisms by which they act on mitochondria. Here we propose a novel mechanism for the direct regulation of mitochondrial gene expression by estrogen under metabolic stress. We show that in serum-depleted medium, estrogen stimulates a rapid relocation of estrogen receptor-α to mitochondria, in which it elicits a cellular response, resulting in an increase in mitochondrial RNA abundance. Mitochondrial RNA levels are regulated through the association of estrogen receptor-α with 17β-hydroxysteroid dehydrogenase 10, a multifunctional protein involved in steroid metabolism that is also a core subunit of the mitochondrial ribonuclease P complex responsible for the cleavage of mitochondrial polycistronic transcripts. Processing of mitochondrial transcripts affects mitochondrial gene expression by controlling the levels of mature RNAs available for translation. This work provides the first mechanism linking RNA processing and estrogen activation in mitochondrial gene expression and underscores the coordinated response between the nucleus and mitochondria in response to stress.

Investigation of sex differences in the expression of RORA and its transcriptional targets in the brain as a potential contributor to the sex bias in autism

Background

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by significant impairment in reciprocal social interactions and communication coupled with stereotyped, repetitive behaviors and restricted interests. Although genomic and functional studies are beginning to reveal some of the genetic complexity and underlying pathobiology of ASD, the consistently reported male bias of ASD remains an enigma. We have recently proposed that retinoic acid-related orphan receptor alpha (RORA), which is reduced in the brain and lymphoblastoid cell lines of multiple cohorts of individuals with ASD and oppositely regulated by male and female hormones, might contribute to the sex bias in autism by differentially regulating target genes, including CYP19A1 (aromatase), in a sex-dependent manner that can also lead to elevated testosterone levels, a proposed risk factor for autism.

Methods

In this study, we examine sex differences in RORA and aromatase protein levels in cortical tissues of unaffected and affected males and females by re-analyzing pre-existing confocal immunofluorescence data from our laboratory. We further investigated the expression of RORA and its correlation with several of its validated transcriptional targets in the orbital frontal cortex and cerebellum as a function of development using RNAseq data from the BrainSpan Atlas of the Developing Human Brain. In a pilot study, we also analyzed the expression of Rora and the same transcriptional targets in the cortex and cerebellum of adult wild-type male and female C57BL/6 mice.

Results

Our findings suggest that Rora/RORA and several of its transcriptional targets may exhibit sexually dimorphic expression in certain regions of the brain of both mice and humans. Interestingly, the correlation coefficients between Rora expression and that of its targets are much higher in the cortex of male mice relative to that of female mice. A strong positive correlation between the levels of RORA and aromatase proteins is also seen in the cortex of control human males and females as well as ASD males, but not ASD females.

Conclusions

Based on these studies, we suggest that disruption of Rora/RORA expression may have a greater impact on males, since sex differences in the correlation of RORA and target gene expression indicate that RORA-deficient males may experience greater dysregulation of genes relevant to ASD in certain brain regions during development.

Electronic supplementary material

The online version of this article (doi:10.1186/2040-2392-6-7) contains supplementary material, which is available to authorized users.

Determination of small molecule ABAD inhibitors crossing blood-brain barrier and pharmacokinetics

A major obstacle to the development of effective treatment of Alzheimer's disease (AD) is successfully delivery of drugs to the brain. We have previously identified a series of benzothiazole phosphonate compounds that block the interaction of amyloid-β peptide with amyloid-β binding alcohol dehydrogenase (ABAD). A selective and sensitive method for the presence of three new benzothiazole ABAD inhibitors in mouse plasma, brain, and artificial cerebrospinal fluid has been developed and validated based on high performance liquid chromatography tandem mass spectrometry. Mass spectra were generated using Micromass Quattro Ultima "triple" quadrupole mass spectrometer equipped with an Electrospray Ionization interface. Good linearity was obtained over a concentration range of 0.05-2.5 μg/ml. The lowest limit of quantification and detection was found to be 0.05 μg/ml. All inter-day accuracies and precisions were within ± 15% of the nominal value and ± 20%, respectively, at the lower limit of quantitation. The tested compounds were stable at various conditions with recoveries >90.0% (RSD <10%). The method used for pharmacokinetic studies of compounds in mouse cerebrospinal fluid, plasma, and brain is accurate, precise, and specific with no matrix effect. Pharmacokinetic data showed that these compounds penetrate the blood-brain barrier (BBB) yielding 4-50 ng/ml peak brain concentrations and 2 μg/ml peak plasma concentrations from a 10 mg/kg dose. These results indicate that our newly synthesized small molecule ABAD inhibitors have a good drug properties with the ability to cross the blood-brain barrier, which holds a great potential for AD therapy.

Molecular insights into HSD10 disease: impact of SDR5C1 mutations on the human mitochondrial RNase P complex

SDR5C1 is an amino and fatty acid dehydrogenase/reductase, moonlighting as a component of human mitochondrial RNase P, which is the enzyme removing 5′-extensions of tRNAs, an early and crucial step in tRNA maturation. Moreover, a subcomplex of mitochondrial RNase P catalyzes the N¹-methylation of purines at position 9, a modification found in most mitochondrial tRNAs and thought to stabilize their structure. Missense mutations in SDR5C1 cause a disease characterized by progressive neurodegeneration and cardiomyopathy, called HSD10 disease. We have investigated the effect of selected mutations on SDR5C1's functions. We show that pathogenic mutations impair SDR5C1-dependent dehydrogenation, tRNA processing and methylation. Some mutations disrupt the homotetramerization of SDR5C1 and/or impair its interaction with TRMT10C, the methyltransferase subunit of the mitochondrial RNase P complex. We propose that the structural and functional alterations of SDR5C1 impair mitochondrial RNA processing and modification, leading to the mitochondrial dysfunction observed in HSD10 patients.

Nuclear-encoded factors involved in post-transcriptional processing and modification of mitochondrial tRNAs in human disease

The human mitochondrial genome (mtDNA) encodes 22 tRNAs (mt-tRNAs) that are necessary for the intraorganellar translation of the 13 mtDNA-encoded subunits of the mitochondrial respiratory chain complexes. Maturation of mt-tRNAs involves 5′ and 3′ nucleolytic excision from precursor RNAs, as well as extensive post-transcriptional modifications. Recent data suggest that over 7% of all mt-tRNA residues in mammals undergo post-transcriptional modification, with over 30 different modified mt-tRNA positions so far described. These processing and modification steps are necessary for proper mt-tRNA function, and are performed by dedicated, nuclear-encoded enzymes. Recent growing evidence suggests that mutations in these nuclear genes (nDNA), leading to incorrect maturation of mt-tRNAs, are a cause of human mitochondrial disease. Furthermore, mtDNA mutations in mt-tRNA genes, which may also affect mt-tRNA function, processing, and modification, are also frequently associated with human disease. In theory, all pathogenic mt-tRNA variants should be expected to affect only a single process, which is mitochondrial translation, albeit to various extents. However, the clinical manifestations of mitochondrial disorders linked to mutations in mt-tRNAs are extremely heterogeneous, ranging from defects of a single tissue to complex multisystem disorders. This review focuses on the current knowledge of nDNA coding for proteins involved in mt-tRNA maturation that have been linked to human mitochondrial pathologies. We further discuss the possibility that tissue specific regulation of mt-tRNA modifying enzymes could play an important role in the clinical heterogeneity observed for mitochondrial diseases caused by mutations in mt-tRNA genes.

Mitochondrial energy failure in HSD10 disease is due to defective mtDNA transcript processing

Muscle, heart and liver were analyzed in a male subject who succumbed to HSD10 disease. Respiratory chain enzyme analysis and BN-PAGE showed reduced activities and assembly of complexes I, III, IV, and V. The mRNAs of all RNase P subunits were preserved in heart and overexpressed in muscle, but MRPP2 protein was severely decreased. RNase P upregulation correlated with increased expression of mitochondrial biogenesis factors and preserved mitochondrial enzymes in muscle, but not in heart where this compensatory mechanism was incomplete. We demonstrate elevated amounts of unprocessed pre-tRNAs and mRNA transcripts encoding mitochondrial subunits indicating deficient RNase P activity. This study provides evidence of abnormal mitochondrial RNA processing causing mitochondrial energy failure in HSD10 disease.

Inborn errors of ketone body utilization

Succinyl-CoA:3-ketoacid CoA transferase (SCOT) deficiency and mitochondrial acetoacetyl-CoA thiolase (beta-ketothiolase or T2) deficiency are classified as autosomal recessive disorders of ketone body utilization characterized by intermittent ketoacidosis. Patients with mutations retaining no residual activity on analysis of expression of mutant cDNA are designated as severe genotype, and patients with at least one mutation retaining significant residual activity, as mild genotype. Permanent ketosis is a pathognomonic characteristic of SCOT-deficient patients with severe genotype. Patients with mild genotype, however, may not have permanent ketosis, although they may develop severe ketoacidotic episodes similar to patients with severe genotype. Permanent ketosis has not been reported in T2 deficiency. In T2-deficient patients with severe genotype, biochemical diagnosis is done on urinary organic acid analysis and blood acylcarnitine analysis to observe characteristic findings during both ketoacidosis and non-episodic conditions. In Japan, however, it was found that T2-deficient patients with mild genotype are common, and typical profiles were not identified on these analyses. Based on a clinical study of ketone body utilization disorders both in Japan and worldwide, we have developed guidelines for disease diagnosis and treatment. These diseases are treatable by avoiding fasting and by providing early infusion of glucose, which enable the patients to grow without sequelae.

The first case in Asia of 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency (HSD10 disease) with atypical presentation

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (2M3HBD) deficiency (HSD10 disease) is a rare inborn error of metabolism, and <30 cases have been reported worldwide. This disorder is typically characterized by progressive neurodegenerative disease from 6 to 18 months of age. Here, we report the first patient with this disorder in Asia, with atypical clinical presentation. A 6-year-old boy, who had been well, presented with severe ketoacidosis following a 5-day history of gastroenteritis. Urinary organic acid analysis showed elevated excretion of 2-methyl-3-hydroxybutyrate and tiglylglycine. He was tentatively diagnosed with β-ketothiolase (T2) deficiency. However, repeated enzyme assays using lymphocytes showed normal T2 activity and no T2 mutation was found. Instead, a hemizygous c.460G>A (p.A154T) mutation was identified in the HSD17B10 gene. This mutation was not found in 258 alleles from Japanese subjects (controls). A normal level of the HSD17B10 protein was found by immunoblot analysis but no 2M3HBD enzyme activity was detected in enzyme assays using the patient's fibroblasts. These data confirmed that this patient was affected with HSD10 disease. He has had no neurological regression until now. His fibroblasts showed punctate and fragmented mitochondrial organization by MitoTracker staining and had relatively low respiratory chain complex IV activity to those of other complexes.

Roles of 17β-hydroxysteroid dehydrogenase type 10 in neurodegenerative disorders

17β-Hydroxysteroid dehydrogenase type 10 (17β-HSD10) is encoded by the HSD17B10 gene mapping at Xp11.2. This homotetrameric mitochondrial multifunctional enzyme catalyzes the oxidation of neuroactive steroids and the degradation of isoleucine. This enzyme is capable of binding to other peptides, such as estrogen receptor α, amyloid-β, and tRNA methyltransferase 10C. Missense mutations of the HSD17B10 gene result in 17β-HSD10 deficiency, an infantile neurodegeneration characterized by progressive psychomotor regression and alteration of mitochondria morphology. 17β-HSD10 exhibits only a negligible alcohol dehydrogenase activity, and is not localized in the endoplasmic reticulum or plasma membrane. Its alternate name - Aβ binding alcohol dehydrogenase (ABAD) - is a misnomer predicated on the mistaken belief that this enzyme is an alcohol dehydrogenase. Misconceptions about the localization and function of 17β-HSD10 abound. 17β-HSD10's proven location and function must be accurately identified to properly assess this enzyme's important role in brain metabolism, especially the metabolism of allopregnanolone. The brains of individuals with Alzheimer's disease (AD) and of animals in an AD mouse model exhibit abnormally elevated levels of 17β-HSD10. Abnormal expression, as well as mutations of the HSD17B10 gene leads to impairment of the structure, function, and dynamics of mitochondria. This may underlie the pathogenesis of the synaptic and neuronal deficiency exhibited in 17β-HSD10 related diseases, including 17β-HSD10 deficiency and AD. Restoration of steroid homeostasis could be achieved by the supplementation of neuroactive steroids with a proper dosing and treatment regimen or by the adjustment of 17β-HSD10 activity to protect neurons. The discovery of this enzyme's true function has opened a new therapeutic avenue for treating AD.

Occasional seizures, epilepsy, and inborn errors of metabolism

Seizures are a common paediatric problem, with inborn errors of metabolism being a rare underlying aetiology. The clinical presentation of inborn errors of metabolism is often associated with other neurological symptoms, such as hypotonia, movement disorders, and cognitive disturbances. However, the occurrence of epilepsy associated with inborn errors of metabolism represents a major challenge that needs to be identified quickly; for some cases, specific treatments are available, metabolic decompensation might be avoided, and accurate counselling can be given about recurrence risk. Some clinical presentations are more likely than others to point to an inborn error of metabolism as the cause of seizures. Knowledge of important findings at examination, and appropriate biochemical investigation of children with seizures of uncertain cause, can aid the diagnosis of an inborn error of metabolism and ascertain whether or not the seizures are amenable to specific metabolic treatment.

Mutation or knock-down of 17β-hydroxysteroid dehydrogenase type 10 cause loss of MRPP1 and impaired processing of mitochondrial heavy strand transcripts

17β-Hydroxysteroid dehydrogenase type 10 (HSD10) is multifunctional protein coded by the X-chromosomal HSD17B10 gene. Mutations in this gene cause HSD10 disease characterized by progressive neurological abnormalities and cardiomyopathy. Disease progression and severity of symptoms is unrelated to the protein's dehydrogenase activity. Recently, it was shown that HSD10 is an essential component of mitochondrial Ribonuclease P (RNase P), an enzyme required for mitochondrial tRNA processing, but little is known about the role of HSD10 in RNase P function. RNase P consists of three different proteins MRPP1, MRPP2 (HSD10) and MRPP3, each of which is essential for RNase P function. Here, we show that HSD10 protein levels are significantly reduced in fibroblasts from patients carrying the HSD17B10 mutation p.R130C. A reduction in HSD10 levels was accompanied by a reduction in MRPP1 protein but not MRPP3 protein. In HSD10 knock-down cells, MRPP1 protein content was also reduced, indicating that HSD10 is important for the maintenance of normal MRPP1 protein levels. Ectopic expression of HSD10 partially restored RNA processing in HSD10 knock-down cells and fibroblasts, and also expression of MRPP1 protein was restored to values comparable to controls. In both, patient fibroblasts and HSD10 knock-down cells, there was evidence of impaired processing of precursor tRNA transcripts of the mitochondrial heavy strand but not the light strand compared with controls. Our findings indicate that HSD10 is important for the maintenance of the MRPP1-HSD10 subcomplex of RNase P and that loss of HSD10 causes impaired mitochondrial precursor transcript processing which may explain mitochondrial dysfunction observed in HSD10 disease.

Physicochemical characteristics of soluble oligomeric Aβand their pathologic role in Alzheimer's disease

Extracellular fibrillar amyloid deposits are prominent and universal Alzheimer's disease (AD) features, but senile plaque abundance does not always correlate directly with the degree of dementia exhibited by AD patients. The mechanism(s) and dynamics of Abeta fibril genesis and deposition remain obscure. Enhanced Abeta synthesis rates coupled with decreased degradative enzyme production and accumulating physical modifications that dampen proteolysis may all enhance amyloid deposit formation. Amyloid accumulation may indirectly exert the greatest pathologic effect on the brain vasculature by destroying smooth muscle cells and creating a cascade of negative impacts on cerebral blood flow. The most visible manifestation of amyloid dis-equilibrium could actually be a defense mechanism employed to avoid serious vascular wall degradation while the major toxic effects to the gray and white matter neurons are mediated by soluble oligomeric Abeta peptides with high beta-sheet content. The recognition that dynamic soluble oligomeric Abeta pools exist in AD and are correlated to disease severity led to neurotoxicity and physical conformation studies. It is now recognized that the most basic soluble Abeta peptides are stable dimers with hydrophobic regions sequestered from the aqueous environment and are capable of higher order aggregations. Time course experiments employing a modified ELISA method able to detect Abeta oligomers revealed dynamic intermolecular interactions and additional experiments physically confirmed the presence of stable amyloid multimers. Amyloid peptides that are rich in beta-sheet structure are capable of creating toxic membrane ion channels and a capacity to self-assemble as annular structures was confirmed in vitro using atomic force microscopy. Biochemical studies have established that soluble Abeta peptides perturb metabolic processes, provoke release of deleterious reactive compounds, reduce blood flow, induce mitochondrial apoptotic toxicity and inhibit angiogenesis. While there is no question that gross amyloid deposition does contribute to AD pathology, the destructive potential now associated with soluble Abeta suggests that treatment strategies that target these molecules may be efficacious in preventing some of the devastating effects of AD.

Comparative proteomics analysis reveals roles for FADD in the regulation of energy metabolism and proteolysis pathway in mouse embryonic fibroblast

Fas-associated death domain-containing protein (FADD) is a classical apoptotic pathway adaptor. Further studies revealed that it also plays essential roles in nonapoptotic processes, which is assumed to be regulated by its phosphorylation. However, the exact mechanisms are still poorly understood. To study the nonapoptotic effects of FADD, a comprehensive strategy of proteomics identification combined with bioinformatic analysis was undertaken to identify proteins differentially expressed in three cell lines containing FADD and its mutant, FADD-A and FADD-D. The cell lines were thought to bear wild-type FADD, unphosphorylated FADD mimic and constitutive phosphorylated FADD mimic, respectively. A total of 47 proteins were identified to be significantly changed due to FADD phosphorylation. Network analysis using MetaCore™ identified a number of changed proteins that were involved in cellular metabolic process, including lipid metabolism, fatty acid metabolism, glycolysis, and oxidative phosphorylation. The finding that FADD-D cell line showed an increase in fatty acid oxidation argues that it could contribute to the leaner phenotype of FADD-D mice as reported previously. In addition, six proteins related to the ubiquitin-proteasome pathway were also specifically overexpressed in FADD-D cell line. Finally, the c-Myc gene represents a convergent hub lying at the center of dysregulated pathways, and was upregulated in FADD-D cells. Taken together, these studies allowed us to conclude that impaired mitochondrial function and proteolysis might play pivotal roles in the dysfunction associated with FADD phosphorylation-induced disorders.

The mitochondrial solute carrier SLC25A5 at Xq24 is a novel candidate gene for non-syndromic intellectual disability

Loss-of-function mutations in several different neuronal pathways have been related to intellectual disability (ID). Such mutations often are found on the X chromosome in males since they result in functional null alleles. So far, microdeletions at Xq24 reported in males always have been associated with a syndromic form of ID due to the loss of UBE2A. Here, we report on overlapping microdeletions at Xq24 that do not include UBE2A or affect its expression, in patients with non-syndromic ID plus some additional features from three unrelated families. The smallest region of overlap, confirmed by junction sequencing, harbors two members of the mitochondrial solute carrier family 25, SLC25A5 and SLC25A43. However, identification of an intragenic microdeletion including SLC25A43 but not SLC25A5 in a healthy boy excluded a role for SLC25A43 in cognition. Therefore, our findings point to SLC25A5 as a novel gene for non-syndromic ID. This highly conserved gene is expressed ubiquitously with high levels in cortex and hippocampus, and a presumed role in mitochondrial exchange of ADP/ATP. Our data indicate that SLC25A5 is involved in memory formation or establishment, which could add mitochondrial processes to the wide array of pathways that regulate normal cognitive functions.

Genome-wide identification of transcriptional targets of RORA reveals direct regulation of multiple genes associated with autism spectrum disorder

BACKGROUND

We have recently identified the nuclear hormone receptor RORA (retinoic acid-related orphan receptor-alpha) as a novel candidate gene for autism spectrum disorder (ASD). Our independent cohort studies have consistently demonstrated the reduction of RORA transcript and/or protein levels in blood-derived lymphoblasts as well as in the postmortem prefrontal cortex and cerebellum of individuals with ASD. Moreover, we have also shown that RORA has the potential to be under negative and positive regulation by androgen and estrogen, respectively, suggesting the possibility that RORA may contribute to the male bias of ASD. However, little is known about transcriptional targets of this nuclear receptor, particularly in humans.

METHODS

Here we identify transcriptional targets of RORA in human neuronal cells on a genome-wide level using chromatin immunoprecipitation (ChIP) with an anti-RORA antibody followed by whole-genome promoter array (chip) analysis. Selected potential targets of RORA were then validated by an independent ChIP followed by quantitative PCR analysis. To further demonstrate that reduced RORA expression results in reduced transcription of RORA targets, we determined the expression levels of the selected transcriptional targets in RORA-deficient human neuronal cells, as well as in postmortem brain tissues from individuals with ASD who exhibit reduced RORA expression.

RESULTS

The ChIP-on-chip analysis reveals that RORA1, a major isoform of RORA protein in human brain, can be recruited to as many as 2,764 genomic locations corresponding to promoter regions of 2,544 genes across the human genome. Gene ontology analysis of this dataset of genes that are potentially directly regulated by RORA1 reveals statistically significant enrichment in biological functions negatively impacted in individuals with ASD, including neuronal differentiation, adhesion and survival, synaptogenesis, synaptic transmission and plasticity, and axonogenesis, as well as higher level functions such as development of the cortex and cerebellum, cognition, memory, and spatial learning. Independent ChIP-quantitative PCR analyses confirm binding of RORA1 to promoter regions of selected ASD-associated genes, including A2BP1, CYP19A1, ITPR1, NLGN1, and NTRK2, whose expression levels (in addition to HSD17B10) are also decreased in RORA1-repressed human neuronal cells and in prefrontal cortex tissues from individuals with ASD.

CONCLUSIONS

Findings from this study indicate that RORA transcriptionally regulates A2BP1, CYP19A1, HSD17B10, ITPR1, NLGN1, and NTRK2, and strongly suggest that reduction of this sex hormone-sensitive nuclear receptor in the brain causes dysregulated expression of these ASD-relevant genes as well as their associated pathways and functions which, in turn, may contribute to the underlying pathobiology of ASD.

Is amyloid binding alcohol dehydrogenase a drug target for treating Alzheimer's disease?

Current strategies for the treatment of Alzheimer's disease (AD) involve tackling the formation or clearance of the amyloid-beta peptide (Aβ) and/or hyper-phosphorylated tau, or the support and stabilization of the remaining neuronal networks. However, as we gain a clearer idea of the large number of molecular mechanisms at work in this disease, it is becoming clearer that the treatment of AD should take a combined approach of dealing with several aspects of the pathology. The concept that we also need to protect specific sensitive targets within the cell should also be considered. In particular the role of protecting the function of a specific mitochondrial protein, amyloid binding alcohol dehydrogenase (ABAD), will be the focus of this review. Mitochondrial dysfunction is a well-recognized fact in the progression of AD, though until recently the mechanisms involved could only be loosely labeled as changes in 'metabolism'. The discovery that Aβ can be present within the mitochondria and specifically bind to ABAD, has opened up a new area of AD research. Here we review the evidence that the prevention of Aβ binding to ABAD is a drug target for the treatment of AD.

Functional specific roles of FADD: comparative proteomic analyses from knockout cell lines

Comparative proteomics identification combined with bioinformatic analyses and cell biology validation revealed novel non-apoptotic functions of FADD in energy metabolism and proteolysis.

A 5-methylcytosine hotspot responsible for the prevalent HSD17B10 mutation

Approximately half of the cases of hydroxysteroid (17β) dehydrogenase X (HSD10) deficiency are due to a missense C>T mutation in exon 4 of the HSD17B10 gene. The resulting HSD10 (p.R130C) loses most or all catalytic functions, and the males with this mutation have a much more severe clinical phenotype than those carrying p.V65A, p.L122V, or p.E249Q mutations. We found that the mutated cytosine which is +2259 nucleotide from the ATG of the gene, is >90% methylated in both the active and inactive X chromosomes in two normal females as well as in the X chromosome of a normal male. Since 5-methylcytosine is prone to conversion to thymine by deamination, the methylation of this cytosine in normal X chromosomes provides an explanation for the prevalence of the p.R130C mutation among patients with HSD10 deficiency. The substitution of arginine for cysteine eliminates several hydrogen bonds and reduces the van der Waals interaction between HSD10 subunits. The resulting disruption of protein structure impairs some if not all of the catalytic and non-enzymatic functions of HSD10. A meta-analysis of residual HSD10 activity in eight patients with the p.R130C mutation showed an average 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) activity of only 6 (±5) % of the normal control level. This is significantly lower than in cells of patients with other, clinically milder mutations and suggests that the loss of HSD10/MHBD activity is a marker for the disorder.

Copy-number gains of HUWE1 due to replication- and recombination-based rearrangements

We previously reported on nonrecurrent overlapping duplications at Xp11.22 in individuals with nonsyndromic intellectual disability (ID) harboring HSD17B10, HUWE1, and the microRNAs miR-98 and let-7f-2 in the smallest region of overlap. Here, we describe six additional individuals with nonsyndromic ID and overlapping microduplications that segregate in the families. High-resolution mapping of the 12 copy-number gains reduced the minimal duplicated region to the HUWE1 locus only. Consequently, increased mRNA levels were detected for HUWE1, but not HSD17B10. Marker and SNP analysis, together with identification of two de novo events, suggested a paternally derived intrachromosomal duplication event. In four independent families, we report on a polymorphic 70 kb recurrent copy-number gain, which harbors part of HUWE1 (exon 28 to 3' untranslated region), including miR-98 and let-7f-2. Our findings thus demonstrate that HUWE1 is the only remaining dosage-sensitive gene associated with the ID phenotype. Junction and in silico analysis of breakpoint regions demonstrated simple microhomology-mediated rearrangements suggestive of replication-based duplication events. Intriguingly, in a single family, the duplication was generated through nonallelic homologous recombination (NAHR) with the use of HUWE1-flanking imperfect low-copy repeats, which drive this infrequent NAHR event. The recurrent partial HUWE1 copy-number gain was also generated through NAHR, but here, the homologous sequences used were identified as TcMAR-Tigger DNA elements, a template that has not yet been reported for NAHR. In summary, we showed that an increased dosage of HUWE1 causes nonsyndromic ID and demonstrated that the Xp11.22 region is prone to recombination- and replication-based rearrangements.

Inborn errors of ketogenesis and ketone body utilization

Ketone bodies acetoacetate and 3-hydroxy-n-butyric acid are metabolites derived from fatty acids and ketogenic amino acids such as leucine. They are mainly produced in the liver via reactions catalyzed by the ketogenic enzymes mitochondrial 3-hydroxy-3-methylglutary-coenzyme A synthase and 3-hydroxy-3-methylglutary-coenzyme A lyase. After prolonged starvation, ketone bodies can provide up to two-thirds of the brain's energy requirements. The rate-limiting enzyme of ketone body utilization (ketolysis) is succinyl-coenzyme A:3-oxoacid coenzyme A transferase. The subsequent step of ketolysis is catalyzed by 2-methylactoacetyl-coenzyme A thiolase, which is also involved in isoleucine catabolism. Inborn errors of metabolism affecting those four enzymes are presented and discussed in the context of differential diagnoses. While disorders of ketogenesis can present with hypoketotic hypoglycemia, inborn errors of ketolysis are characterized by metabolic decompensations with ketoacidosis. If those diseases are considered early and appropriate treatment is initiated without delay, patients with inborn errors of ketone body metabolism often have a good clinical outcome.

HSD10 disease: clinical consequences of mutations in the HSD17B10 gene

The HSD17B10 gene is located on chromosome Xp11.2 and codes for a multifunctional protein called 17β-hydroxysteroid dehydrogenase type 10 (HSD10). This protein catalyzes the 2-methyl-3-hydroxybutyryl-CoA dehydrogenation (MHBD) reaction in isoleucine metabolism and is an essential component of mitochondrial RNase P required for the processing of mtDNA transcripts. HSD10 is required for normal mitochondrial maintenance, and complete loss of HSD10 is incompatible with life. Mutations in the HSD17B10 gene have been reported in 19 families. The classical infantile form of what is best named HSD10 disease is characterized by a period of more or less normal development in the first 6-18 months of life. Some patients showed transient metabolic derangement in the neonatal period, with good clinical recovery but often persistent lactate elevation. Usually from age 6-18 months affected boys show a progressive neurodegenerative disease course in conjunction with retinopathy and cardiomyopathy leading to death at age 2-4 years or later. A more severe presentation in the neonatal period with little neurological development, severe progressive cardiomyopathy, and early death, is denoted neonatal form. Juvenile and atypical/asymptomatic forms of HSD10 disease have been recognized. Heterozygous females often show non-progressive developmental delay and intellectual disability but may also be clinically normal. The pathogenesis is poorly understood but is unrelated to MHBD function. Diagnosis is based on typical abnormalities in urinary organic acid analysis and molecular studies. The same de novo mutation p.R130C was found in over half of patient families; it is associated with the infantile disease form. There is no effective treatment.

Of P and Z: mitochondrial tRNA processing enzymes

Mitochondrial tRNAs are generally synthesized as part of polycistronic transcripts. Release of tRNAs from these precursors is thus not only required to produce functional adaptors for translation, but also responsible for the maturation of other mitochondrial RNA species. Cleavage of mitochondrial tRNAs appears to be exclusively accomplished by endonucleases. 5'-end maturation in the mitochondria of different Eukarya is achieved by various kinds of RNase P, representing the full range of diversity found in this enzyme family. While ribonucleoprotein enzymes with RNA components of bacterial-like appearance are found in a few unrelated protists, algae, and fungi, highly degenerate RNAs of dramatic size variability are found in the mitochondria of many fungi. The majority of mitochondrial RNase P enzymes, however, appear to be pure protein enzymes. Human mitochondrial RNase P, the first to be identified and possibly the prototype of all animal mitochondrial RNases P, is composed of three proteins. Homologs of its nuclease subunit MRPP3/PRORP, are also found in plants, algae and several protists, where they are apparently responsible for RNase P activity in mitochondria (and beyond) without the help of extra subunits. The diversity of RNase P enzymes is contrasted by the uniformity of mitochondrial RNases Z, which are responsible for 3'-end processing. Only the long form of RNase Z, which is restricted to eukarya, is found in mitochondria, even when an additional short form is present in the same organism. Mitochondrial tRNA processing thus appears dominated by new, eukaryal inventions rather than bacterial heritage. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.

A novel mutation in the HSD17B10 gene of a 10-year-old boy with refractory epilepsy, choreoathetosis and learning disability

Hydroxysteroid (17beta) dehydrogenase 10 (HSD10) is a mitochondrial multifunctional enzyme encoded by the HSD17B10 gene. Missense mutations in this gene result in HSD10 deficiency, whereas a silent mutation results in mental retardation, X-linked, syndromic 10 (MRXS10). Here we report a novel missense mutation found in the HSD17B10 gene, namely c.194T>C transition (rs104886492), brought about by the loss of two forked methyl groups of valine 65 in the HSD10 active site. The affected boy, who possesses mutant HSD10 (p.V65A), has a neurological syndrome with metabolic derangements, choreoathetosis, refractory epilepsy and learning disability. He has no history of acute decompensation or metabolic acidosis whereas his urine organic acid profile, showing elevated levels of 2-methyl-3-hydroxybutyrate and tiglylglycine, is characteristic of HSD10 deficiency. His HSD10 activity was much lower than the normal control level, with normal β-ketothiolase activity. The c.194T>C mutation in HSD17B10 can be identified by the restriction fragment polymorphism analysis, thereby facilitating the screening of this novel mutation in individuals with intellectual disability of unknown etiology and their family members much easier. The patient's mother is an asymptomatic carrier, and has a mixed ancestry (Hawaiian, Japanese and Chinese). This demonstrates that HSD10 deficiency patients are not confined to a particular ethnicity although previously reported cases were either Spanish or German descendants.