Optic atrophy 1 (OPA1) is a mitochondrial inner membrane protein that has an important role in mitochondrial fusion and structural integrity. Dysfunctional OPA1 mutations cause atrophy of the optic nerve leading to blindness. Here, we show that OPA1 has an important role in the innate immune system. Using conditional knockout mice lacking Opa1 in neutrophils (Opa1^N∆), we report that lack of OPA1 reduces the activity of mitochondrial electron transport complex I in neutrophils. This then causes a decline in adenosine-triphosphate (ATP) production through glycolysis due to lowered NAD⁺availability. Additionally, we show that OPA1-dependent ATP production in these cells is required for microtubule network assembly and for the formation of neutrophil extracellular traps. Finally, we show thatOpa1^N∆mice exhibit a reduced antibacterial defense capability againstPseudomonas aeruginosa.

The hairpin structure at the 3′ end of animal histone mRNAs controls histone RNA 3′ processing, nucleo‐cytoplasmic transport, translation and stability of histone mRNA. Functionally overlapping, if not identical, proteins binding to the histone RNA hairpin have been identified in nuclear and polysomal extracts. Our own results indicated that these hairpin binding proteins (HBPs) bind their target RNA as monomers and that the resulting ribonucleoprotein complexes are extremely stable. These features prompted us to select for HBP‐encoding human cDNAs by RNA‐mediated three‐hybrid selection in Saccharomyces cerevesiae . Whole cell extract from one selected clone contained a Gal4 fusion protein that interacted with histone hairpin RNA in a sequence‐ and structure‐specific manner similar to a fraction enriched for bovine HBP, indicating that the cDNA encoded HBP. DNA sequence analysis revealed that the coding sequence did not contain any known RNA binding motifs. The HBP gene is composed of eight exons covering 19.5 kb on the short arm of chromosome 4. Translation of the HBP open reading frame in vitro produced a 43 kDa protein with RNA binding specificity identical to murine or bovine HBP. In addition, recombinant HBP expressed in S.cerevisiae was functional in histone pre‐mRNA processing, confirming that we have indeed identified the human HBP gene.

Hypomagnesemia affects insulin resistance and is a risk factor for diabetes mellitus type 2 (DM2) and gestational diabetes mellitus (GDM). Two single nucleotide polymorphisms (SNPs) in the epithelial magnesium channel TRPM6 (V ¹³⁹³ I, K ¹⁵⁸⁴ E) were predicted to confer susceptibility for DM2. Here, we show using patch clamp analysis and total internal reflection fluorescence microscopy, that insulin stimulates TRPM6 activity via a phosphoinositide 3-kinase and Rac1-mediated elevation of cell surface expression of TRPM6. Interestingly, insulin failed to activate the genetic variants TRPM6(V ¹³⁹³ I) and TRPM6(K ¹⁵⁸⁴ E), which is likely due to the inability of the insulin signaling pathway to phosphorylate TRPM6(T ¹³⁹¹ ) and TRPM6(S ¹⁵⁸³ ). Moreover, by measuring total glycosylated hemoglobin (TGH) in 997 pregnant women as a measure of glucose control, we demonstrate that TRPM6(V ¹³⁹³ I) and TRPM6(K ¹⁵⁸⁴ E) are associated with higher TGH and confer a higher likelihood of developing GDM. The impaired response of TRPM6(V ¹³⁹³ I) and TRPM6(K ¹⁵⁸⁴ E) to insulin represents a unique molecular pathway leading to GDM where the defect is located in TRPM6.

Objective: Short‐chain enoyl‐CoA hydratase (ECHS1) is a multifunctional mitochondrial matrix enzyme that is involved in the oxidation of fatty acids and essential amino acids such as valine. Here, we describe the broad phenotypic spectrum and pathobiochemistry of individuals with autosomal‐recessive ECHS1 deficiency.Methods: Using exome sequencing, we identified ten unrelated individuals carrying compound heterozygous or homozygous mutations in ECHS1. Functional investigations in patient‐derived fibroblast cell lines included immunoblotting, enzyme activity measurement, and a palmitate loading assay.Results: Patients showed a heterogeneous phenotype with disease onset in the first year of life and course ranging from neonatal death to survival into adulthood. The most prominent clinical features were encephalopathy (10/10), deafness (9/9), epilepsy (6/9), optic atrophy (6/10), and cardiomyopathy (4/10). Serum lactate was elevated and brain magnetic resonance imaging showed white matter changes or a Leigh‐like pattern resembling disorders of mitochondrial energy metabolism. Analysis of patients’ fibroblast cell lines (6/10) provided further evidence for the pathogenicity of the respective mutations by showing reduced ECHS1 protein levels and reduced 2‐enoyl‐CoA hydratase activity. While serum acylcarnitine profiles were largely normal, in vitro palmitate loading of patient fibroblasts revealed increased butyrylcarnitine, unmasking the functional defect in mitochondrial β‐oxidation of short‐chain fatty acids. Urinary excretion of 2‐methyl‐2,3‐dihydroxybutyrate – a potential derivative of acryloyl‐CoA in the valine catabolic pathway – was significantly increased, indicating impaired valine oxidation.Interpretation: In conclusion, we define the phenotypic spectrum of a new syndrome caused by ECHS1 deficiency. We speculate that both the β‐oxidation defect and the block in l‐valine metabolism, with accumulation of toxic methacrylyl‐CoA and acryloyl‐CoA, contribute to the disorder that may be amenable to metabolic treatment approaches.

Background: Defects of the mitochondrial respiratory chain complex II (succinate dehydrogenase (SDH) complex) are extremely rare. Of the four nuclear encoded proteins composing complex II, only mutations in the 70 kDa flavoprotein (SDHA) and the recently identified complex II assembly factor (SDHAF1) have been found to be causative for mitochondrial respiratory chain diseases. Mutations in the other three subunits (SDHB, SDHC, SDHD) and the second assembly factor (SDHAF2) have so far only been associated with hereditary paragangliomas and phaeochromocytomas. Recessive germline mutations in SDHB have recently been associated with complex II deficiency and leukodystrophy in one patient. Methods and results: We present the clinical and molecular investigations of the first patient with biochemical evidence of a severe isolated complex II deficiency due to compound heterozygous SDHD gene mutations. The patient presented with early progressive encephalomyopathy due to compound heterozygous p.E69 K and p.*164Lext*3 SDHD mutations. Native polyacrylamide gel electrophoresis and western blotting demonstrated an impaired complex II assembly. Complementation of a patient cell line additionally supported the pathogenicity of the novel identified mutations in SDHD. Conclusions: This report describes the first case of isolated complex II deficiency due to recessive SDHD germline mutations. We therefore recommend screening for all SDH genes in isolated complex II deficiencies. It further emphasises the importance of appropriate genetic counselling to the family with regard to SDHD mutations and their role in tumorigenesis.