The morphology of mitochondria in mammalian cells is regulated by proteolytic cleavage of OPA1, a dynamin-like GTPase of the mitochondrial inner membrane. The mitochondrial rhomboid protease PARL, ...and paraplegin, a subunit of the ATP-dependent m-AAA protease, were proposed to be involved in this process. Here, we characterized individual OPA1 isoforms by mass spectrometry, and we reconstituted their processing in yeast to identify proteases involved in OPA1 cleavage. The yeast homologue of OPA1, Mgm1, was processed both by PARL and its yeast homologue Pcp1. Neither of these rhomboid proteases cleaved OPA1. The formation of small OPA1 isoforms was impaired in yeast cells lacking the m-AAA protease subunits Yta10 and Yta12 and was restored upon expression of murine or human m-AAA proteases. OPA1 processing depended on the subunit composition of mammalian m-AAA proteases. Homo-oligomeric m-AAA protease complexes composed of murine Afg3l1, Afg3l2, or human AFG3L2 subunits cleaved OPA1 with higher efficiency than paraplegin-containing m-AAA proteases. OPA1 processing proceeded normally in murine cell lines lacking paraplegin or PARL. Our results provide evidence for different substrate specificities of m-AAA proteases composed of different subunits and reveal a striking evolutionary switch of proteases involved in the proteolytic processing of dynamin-like GTPases in mitochondria.
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The natural capacity of extracellular vesicles (EVs) to transport their payload to recipient cells has raised big interest to repurpose EVs as delivery vehicles for xenobiotics. In ...the present study, bovine milk-derived EVs (BMEVs) were investigated for their potential to shuttle locked nucleic acid-modified antisense oligonucleotides (LNA ASOs) into the systemic circulation after oral administration. To this end, a broad array of analytical methods including proteomics and lipidomics were used to thoroughly characterize BMEVs. We found that additional purification by density gradients efficiently reduced levels of non-EV associated proteins. The potential of BMEVs to functionally transfer LNA ASOs was tested using advanced in vitro systems (i.e. hPSC-derived neurons and primary human cells). A slight increase in cellular LNA ASO internalization and target gene reduction was observed when LNA ASOs were delivered using BMEVs. When dosed orally in mice, only a small fraction (about 1% of total administered dose) of LNA ASOs was recovered in the peripheral tissues liver and kidney, however, no significant reduction in target gene expression (i.e. functional knockdown) was observed.
Autism spectrum disorder (ASD) is characterized by deficits in language development and social cognition and the manifestation of repetitive and restrictive behaviors. Despite recent major advances, ...our understanding of the pathophysiological mechanisms leading to ASD is limited. Although most ASD cases have unknown genetic underpinnings, animal and human cellular models of several rare, genetically defined syndromic forms of ASD have provided evidence for shared pathophysiological mechanisms that may extend to idiopathic cases. Here, we review our current knowledge of the genetic basis and molecular etiology of ASD and highlight how human pluripotent stem cell-based disease models have the potential to advance our understanding of molecular dysfunction. We summarize landmark studies in which neuronal cell populations generated from human embryonic stem cells and patient-derived induced pluripotent stem cells have served to model disease mechanisms, and we discuss recent technological advances that may ultimately allow in vitro modeling of specific human neuronal circuitry dysfunction in ASD. We propose that these advances now offer an unprecedented opportunity to help better understand ASD pathophysiology. This should ultimately enable the development of cellular models for ASD, allowing drug screening and the identification of molecular biomarkers for patient stratification.
Tuberous sclerosis complex (TSC) is a genetic disease characterized by benign tumor growths in multiple organs and neurological symptoms induced by mTOR hyperfunction. Because the molecular pathology ...is highly complex and the etiology poorly understood, we employed a defined human neuronal model with a single mTOR activating mutation to dissect the disease-relevant molecular responses driving the neuropathology and suggest new targets for treatment.
We investigate the disease phenotype of TSC by neural differentiation of a human stem cell model that had been deleted for TSC2 by genome editing. Comprehensive genomic analysis was performed by RNA sequencing and ribosome profiling to obtain a detailed genome-wide description of alterations on both the transcriptional and translational level. The molecular effect of mTOR inhibitors used in the clinic was monitored and comparison to published data from patient biopsies and mouse models highlights key pathogenic processes.
TSC2-deficient neural stem cells showed severely reduced neuronal maturation and characteristics of astrogliosis instead. Transcriptome analysis indicated an active inflammatory response and increased metabolic activity, whereas at the level of translation ribosomal transcripts showed a 5'UTR motif-mediated increase in ribosome occupancy. Further, we observed enhanced protein synthesis rates of angiogenic growth factors. Treatment with mTOR inhibitors corrected translational alterations but transcriptional dysfunction persisted.
Our results extend the understanding of the molecular pathophysiology of TSC brain lesions, and suggest phenotype-tailored pharmacological treatment strategies.
Rationale
The main reason for the current lack of effective treatments for the core symptoms of autism is our limited understanding of the biological mechanisms underlying this heterogeneous group of ...disorders. A primary value of genetic research is enhancing our insight into the biology of autism through the study of identified autism risk genes.
Objectives
In the current review we discuss (1) the genes and loci that are associated with autism, (2) how these provide us with essential cues as to what neurobiological mechanisms may be involved, and (3) how these mechanisms may be used as targets for novel treatments. Next, we provide an overview of currently ongoing clinical trials registered at clinicaltrials.gov with a variety of compounds. Finally, we review current approaches used to translate knowledge derived from gene discovery into novel pharmaceutical compounds and discuss their pitfalls and problems.
Conclusions
An increasing number of genetic variants associated with autism have been identified. This will generate new ideas about the biological mechanisms involved in autism, which in turn may provide new leads for the development of novel pharmaceutical compounds. To optimize this pipeline of drug discovery, large-scale international collaborations are needed for gene discovery, functional validation of risk genes, and improvement of clinical outcome measures and clinical trial methodology in autism.
Purpose
Human pluripotent stem cell (hPSC)‐derived cellular models have great potential to enable drug discovery and improve translation of preclinical insights to the clinic. We have developed a ...hPSC‐derived neural precursor cell model for studying early events in human brain development. We present protein‐level characterization of this model, using a multiplexed SRM approach, to establish reproducibility and physiological relevance; essential prerequisites for utilization of the neuronal development model in phenotypic screening‐based drug discovery.
Experimental design
Profiles of 246 proteins across three key stages of in vitro neuron differentiation were analyzed by SRM. Three independently hPSC‐derived isogenic neural stem cell (NSC) lines were analyzed across five to nine independent neuronal differentiations.
Results
One hundred seventy‐five proteins were reliably quantified revealing a time‐dependent pattern of protein regulation that reflected protein dynamics during in vivo brain development and that was conserved across replicate differentiations and multiple cell lines.
Conclusions and clinical relevance
SRM‐based protein profiling enabled establishment of the reproducibility and physiological relevance of the hPSC‐derived neuronal model. Combined with the successful quantification of proteins relevant to neurodevelopmental diseases, this validates the platform for use as a model to enable neuroscience drug discovery.
Genetic, preclinical and clinical data link Parkinson's disease and Gaucher's disease and provide a rational entry point to disease modification therapy via enhancement of β‐Glucocerebrosidase ...(GCase) activity. We discovered a new class of pyrrolo2,3‐bpyrazine activators effecting both Vmax and Km. They bind to human GCase and increase substrate metabolism in the lysosome in a cellular assay. We obtained the first crystal structure for an activator and identified a novel non‐inhibitory binding mode at the interface of a dimer, rationalizing the observed structure–activity relationship (SAR). The compound binds GCase inducing formation of a dimeric state at both endoplasmic reticulum (ER) and lysosomal pHs, as confirmed by analytical ultracentrifugation. Importantly, the pyrrolo2,3‐bpyrazines have central nervous system (CNS) drug‐like properties. Our findings are important for future drug discovery efforts in the field of GCase activation and provide a deeper mechanistic understanding of the requirements for enzymatic activation, pointing to the relevance of dimerization.
A first crystal structure for a novel GCase activator is obtained and a novel non‐inhibitory binding mode at a dimer interface, rationalizing the observed structure–activity relationship, is identified. Mechanistic insights and key information for future drug discovery efforts towards GCase activation are provided.
Adult neural stem cells hold great promise for repair because of their unique location within the central nervous system, their potential to proliferate and to differentiate into all major neural ...lineages, and their ability to incorporate functionally into the existing neuronal circuitry. However, recruitment of these cells for repair is hampered by the lack of knowledge about the signals that control the generation of a functional neuron from adult neural stem cells. Here, we discuss recent findings on the regulatory mechanisms that underlie neurogenesis from neural stem cells in the adult hippocampus and the implications of these findings for future stem-cell-based repair strategies.
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