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Adriaenssens et al. provide evidence suggesting that cytosolic small heat shock proteins localize to the mitochondrial intermembrane space, where they operate as molecular chaperones. Mitochondria are complex organelles with different compartments, each harbouring their own protein quality control factors. While chaperones of the mitochondrial matrix are well characterized, it is poorly understood which chaperones protect the mitochondrial intermembrane space. Here we show that cytosolic small heat shock proteins are imported under basal conditions into the mitochondrial intermembrane space, where they operate as molecular chaperones. Protein misfolding in the mitochondrial intermembrane space leads to increased recruitment of small heat shock proteins. Depletion of small heat shock proteins leads to mitochondrial swelling and reduced respiration, while aggregation of aggregation-prone substrates is countered in their presence. Charcot-Marie-Tooth disease-causing mutations disturb the mitochondrial function of HSPB1, potentially linking previously observed mitochondrial dysfunction in Charcot-Marie-Tooth type 2F to its role in the mitochondrial intermembrane space. Our results reveal that small heat shock proteins form a chaperone system that operates in the mitochondrial intermembrane space.

PURPOSE CTR9 is a subunit of the PAF1 complex (PAF1C) that plays a crucial role in transcription regulation by binding CTR9 to RNA polymerase II. It is involved in transcription-coupled histone modification through promoting H3K4 and H3K36 methylation. We describe the clinical and molecular studies in 13 probands, harboring likely pathogenic CTR9 missense variants, collected through GeneMatcher. METHODS Exome sequencing was performed in all individuals. CTR9 variants were assessed through 3-dimensional modeling of the activated human transcription complex Pol II-DSIF-PAF-SPT6 and the PAF1/CTR9 complex. H3K4/H3K36 methylation analysis, mitophagy assessment based on tetramethylrhodamine ethyl ester perchlorate immunofluorescence, and RNA-sequencing in skin fibroblasts from 4 patients was performed. RESULTS Common clinical findings were variable degrees of intellectual disability, hypotonia, joint hyperlaxity, speech delay, coordination problems, tremor, and autism spectrum disorder. Mild dysmorphism and cardiac anomalies were less frequent. For 11 CTR9 variants, de novo occurrence was shown. Three-dimensional modeling predicted a likely disruptive effect of the variants on local CTR9 structure and protein interaction. Additional studies in fibroblasts did not unveil the downstream functional consequences of the identified variants. CONCLUSION We describe a neurodevelopmental disorder caused by (mainly) de novo variants in CTR9, likely affecting PAF1C function.

The present review aims to examine the effect of specific drugs on long-term outcome of pulmonary arterial hypertension (PAH), to critically review the available data, and to derive useful information for daily patient care. PAH is an intrinsic disease of the pulmonary circulation with a malignant evolution as a consequence of progressive right heart failure. Without specific therapy, median survival is only 2.8 yrs. The intravenous prostacyclin analogue epoprostenol is the only treatment with a demonstrated effect on survival, observed during a single 12-week randomised placebo-controlled trial. Three long-term observational studies have also shown that median survival is raised above 6 yrs with this therapy. Subcutaneous treprostinil appears to have similar beneficial effects on survival, as reported in two long-term observational studies. This is not the case for inhaled iloprost, as shown in one study in which a high proportion of patients needed the addition of, or the switch to, another therapy. Among the oral agents, long-term data have only been published for bosentan. The three studies including patients from expert centres also showed very good survival data, but again with a broad use of combination therapy. In less expert hands, with limited access to more complex therapies, reported survival seems much worse. In these studies, baseline New York Heart Association class and 6-min walk distance are repeatedly shown to be important predictors of survival. Finally, there is emerging data that prostanoid therapy results in a tendency to normalise C-reactive protein levels, a factor associated with improved long-term outcomes. ispartof: European Respiratory Review vol:18 issue:114 pages:253-259 ispartof: location:England status: published