Biology subjects

Pfeffer, G.

Publications and source records attributed to Pfeffer, G..

8 recordsLinked to original sources

bioRxiv2026

Altered Steroidogenesis in Response to Impaired Mitochondrial Protein Homeostasis

Mitochondrial proteostasis is critical for organelle function, but how it influences mitochondrial steroidogenesis is not understood. We investigated the impact of impaired mitochondrial proteostasis on mitochondrial protein import and how this impacts cortisol production. We found that mild mitochondrial proteostatic stress increased cortisol synthesis whereas severe stress suppressed cortisol, revealing a biphasic steroidogenic response. Mild stress induced increases in cholesterol import and cortisol production in a manner dependent on STARD1-mediated cholesterol transport, which is the first and rate-limiting step in steroidogenesis. Severe stress reduced cortisol synthesis independently of STARD1 activity, indicating this inhibition occurs downstream in steroidogenesis. These findings reveal mitochondrial protein import as a regulatory node linking mitochondrial proteostasis to steroidogenic output. Furthermore, we observed increased cortisol synthesis in rotenone, A53T alpha-synuclein and PINK1-KO models of PD, suggesting that this response is relevant to PD-associated mitochondrial dysfunction. Together, our findings reveal a biphasic steroidogenic response to impairments in mitochondrial quality control with implications in human disease. Our work recognizes a previously unexplored branch of the mitochondrial stress response that enables cellular and physiological adaptations that can be detrimental if constitutively activated.

cell biology↗

bioRxiv2024

The gut microbiota is a determinant of sexual dimorphism in ALS-linked TDP43 mice

The mechanisms underlying the earlier onset and male predominance of amyotrophic lateral sclerosis (ALS), the most common form of human motoneuron disease, are poorly understood. Here we show that the gut microbiota protects against TDP43 toxicity and contributes to the sexual dimorphism in mice expressing a mutant form of TDP43 (A315T) linked to ALS. TDP43 mice raised under germ-free conditions, or treated with antibiotics to deplete the gut microbiota, develop motoneuron disease earlier and show no sex differences in onset and lifespan. Behavioral and histopathological analyses confirm the exacerbation in neurodegeneration caused by the absence of gut microbiota. Castration did not alter disease course of male TDP43 mice, suggesting that male sex hormones do not interact with the gut microbiota to confer disease phenotype. Future identification of gut bacteria species and their mechanisms of action offers a unique opportunity to understand sexual dimorphism in ALS, with the ultimate goal to develop non-invasive and sex-specific treatments for ALS.

physiology↗

bioRxiv2024

Pharmacologic Activation of Integrated Stress Response Kinases Inhibits Pathologic Mitochondrial Fragmentation

Excessive mitochondrial fragmentation is associated with the pathologic mitochondrial dysfunction implicated in the pathogenesis of etiologically-diverse diseases, including many neurodegenerative disorders. The integrated stress response (ISR) - comprising the four eIF2 kinases PERK, GCN2, PKR, and HRI - is a prominent stress-responsive signaling pathway that regulates mitochondrial morphology and function in response to diverse types of pathologic insult. This suggests that pharmacologic activation of the ISR represents a potential strategy to mitigate pathologic mitochondrial fragmentation associated with human disease. Here, we show that pharmacologic activation of the ISR kinases HRI or GCN2 promotes adaptive mitochondrial elongation and prevents mitochondrial fragmentation induced by the calcium ionophore ionomycin. Further, we show that pharmacologic activation of the ISR reduces mitochondrial fragmentation and restores basal mitochondrial morphology in patient fibroblasts expressing the pathogenic D414V variant of the pro-fusion mitochondrial GTPase MFN2 associated with neurological dysfunctions including ataxia, optic atrophy, and sensorineural hearing loss. These results identify pharmacologic activation of ISR kinases as a potential strategy to prevent pathologic mitochondrial fragmentation induced by disease-relevant chemical and genetic insults, further motivating the pursuit of highly selective ISR kinase-activating compounds as a therapeutic strategy to mitigate mitochondrial dysfunction implicated in diverse human diseases.

cell biology↗

bioRxiv2022

A Protocol for Single Nucleus RNAseq from Frozen Skeletal Muscle

Single cell technologies are a method of choice to obtain vast amounts of cell-specific transcriptional information under physiological and diseased states. Myogenic cells are resistant to single nucleus RNA sequencing (snRNAseq) due to their large, multinucleated nature. Here, we report a novel, reliable, and cost-effective method to analyze frozen human skeletal muscle by snRNAseq. This method yields all expected cell types for human skeletal muscle and works on tissue frozen for long periods of time and with significant pathological changes. Our method is ideal for studying banked samples with the intention of studying human muscle disease.

genomics↗

bioRxiv2022

Single molecule long-read real-time amplicon-based sequencing of CYP2D6: a proof-of-concept with hybrid haplotypes

CYP2D6 is a widely expressed human xenobiotic metabolizing enzyme, best known for its role in the hepatic phase I cytochrome P450 enzyme system, where it metabolizes [~]20% of medications. It is also expressed in other organs including the brain, where its potential role in physiology and mental health traits and disorders is under further investigation. Owing to the presence of homologous pseudogenes in the CYP2D locus and transposable repeat elements in the intergenic regions, the gene encoding the CYP2D6 enzyme, CYP2D6, is one of the most hypervariable known human genes - with more than 165 core haplotypes. Haplotypes include structural variants, with a subtype of these known as hybrid haplotypes or fusion genes comprising part of CYP2D6 and part of its adjacent pseudogene, CYP2D7. The fusion genes are particularly challenging to identify. High fidelity (HiFi) single molecule real-time (SMRT) long-read sequencing can cover whole CYP2D6 haplotypes in a single continuous sequence, and is therefore ideal for structural variant detection. In addition, it is highly accurate and suitable for novel haplotype identification, which is necessary as new CYP2D6 haplotypes are continuously being discovered, and many more likely remain to be identified in relatively understudied populations such as Indigenous Peoples. The aim of the present work was to develop an efficient and accurate HiFi SMRT amplicon-based method capable of detecting the full range of CYP2D6 haplotypes including fusion genes. We report proof-of-concept for 24 amplicons including three positive controls, aligned to fusion gene haplotypes, with prior cross-validation data. Amplicons with CYP2D7-D6 fusion genes, including positive controls, aligned to the *13 subhaplotypes predicted (*13F, *13A2) with 100% accuracy, with the exception of one that aligned at 99.9%. Alignment of the *68 was 100% and above 99.9% to the CYP2D6*68 partial sequences EU5300606 and JF307779, respectively. The best alignments for the remaining CYP2D6-2D7 fusion genes were [≥]99.7% (to 3 significant figures). Lower percentage alignment for CYP2D6-2D7 fusion genes may reflect imperfect PCR optimization and/or the possibility that we may have haplotypes not yet in public databases. Further work on these is in progress. Moreover, we have adapted this method for non-hybrid haplotypes. This technique could therefore suffice for the characterization of the full range of CYP2D6 haplotypes. The method that we have developed could be extended to other complex loci and to other species in a multiplexed high throughput assay.

genomics↗

bioRxiv2021

Mitochondrial fission is required for proper nucleoid distribution within mitochondrial networks

Mitochondrial DNA (mtDNA) maintenance is essential to sustain a functionally healthy population of mitochondria within cells. Proper mtDNA replication and distribution within mitochondrial networks are essential to maintain mitochondrial homeostasis. However, the fundamental basis of mtDNA segregation and distribution within mitochondrial networks is still unclear. To address these questions, we developed an algorithm, Mitomate tracker to unravel the global distribution of nucleoids within mitochondria. Using this tool, we decipher the semi-regular spacing of nucleoids across mitochondrial networks. Furthermore, we show that mitochondrial fission actively regulates mtDNA distribution by controlling the distribution of nucleoids within mitochondrial networks. Specifically, we found that primary cells bearing disease-associated mutations in the fission proteins DRP1 and MYH14 show altered nucleoid distribution, and acute enrichment of enlarged nucleoids near the nucleus. Further analysis suggests that the altered nucleoid distribution observed in the fission mutants is the result of both changes in network structure and nucleoid density. Thus, our study provides novel insights into the role of mitochondria fission in nucleoid distribution and the understanding of diseases caused by fission defects. Significance statementMutation or deletion of mitochondrial DNA (mtDNA) is associated with a large number of human diseases. However, the mechanisms controlling mtDNA replication and segregation are still poorly understood. Here, we have developed a new computational method to quantify the distribution of nucleoids (mtDNA with associated proteins) and define how nucleoid distribution is affected by changes in mitochondrial network structure. We demonstrate that mitochondrial fission is required for the proper distribution of nucleoids across mitochondrial networks, cells from patients with fission defects showing irregular nucleoid distribution and perinuclear accumulation. Nonetheless, each fission mutant behaved in a distinct manner, indicating a complex relationship between mitochondrial dynamics and nucleoid distribution.

cell biology↗

bioRxiv2021

Characterization of a novel variant in the HR1 domain of MFN2 in a patient with ataxia, optic atrophy and sensorineural hearing loss

Pathogenic variants in MFN2 cause Charcot-Marie-Tooth disease (CMT) type 2A (CMT2A) and are the leading cause of the axonal subtypes of CMT. CMT2A is characterized by predominantly distal motor weakness and muscle atrophy, with highly variable severity and onset age. Notably, some MFN2 variants can also lead to other phenotypes such as optic atrophy, hearing loss and lipodystrophy. Despite the clear link between MFN2 and CMT2A, our mechanistic understanding of how dysfunction of the MFN2 protein causes human disease pathologies remains incomplete. This lack of understanding is due in part to the multiple cellular roles of MFN2. Though initially characterized for its role in mediating mitochondrial fusion, MFN2 also plays important roles in mediating interactions between mitochondria and other organelles, such as the endoplasmic reticulum and lipid droplets. Additionally, MFN2 is also important for mitochondrial transport, mitochondrial autophagy, and has even been implicated in lipid transfer. Though over 100 pathogenic MFN2 variants have been described to date, only a few have been characterized functionally, and even then, often only for one or two functions. Here, we describe a novel homozygous MFN2 variant, D414V, in a patient presenting with cerebellar ataxia, deafness, blindness, and diffuse cerebral and cerebellar atrophy. Characterization of patient fibroblasts reveals phenotypes consistent with impaired MFN2 functions and expands the phenotypic presentation of MFN2 variants to include cerebellar ataxia.

genetics↗

bioRxiv2019

Cross-validation of technologies for genotyping CYP2D6 and CYP2C19

BackgroundCYP2D6 and CYP2C19 are cytochrome P450 enzymes involved in the metabolism of many medications from multiple therapeutic classes. Associations between patterns of variants (known as haplotypes) in the genes encoding them (CYP2D6 and CYP2C19) and enzyme activities are well described. The genes in fact comprise 21% of biomarkers in drug labels. Despite this, genotyping is not common, partly attributable to its challenging nature (CYP2D6 having >100 haplotypes, including those with sequence from an adjacent pseudogene, and gene duplications). We cross-validated different methodologies for identifying haplotypes in these genes against each other. MethodsNinety-two samples with a variety of CYP2D6 and CYP2C19 genotypes according to prior AmpliChip CYP450 and TaqMan CYP2C19*17 data were selected from the Genome-based therapeutic drugs for depression (GENDEP) study. Genotyping was performed with TaqMan copy number variant (CNV) and single nucleotide variant (SNV) analysis, the next generation sequencing-based Ion S5 AmpliSeq Pharmacogenomics Panel, PharmacoScan, long-range polymerase chain reaction (L-PCR) followed by amplicon analysis, and Agena for CYP2C19. Variant pattern to haplotype translation was automated. ResultsThe inter-platform concordance for CYP2C19 was high (up to 100% for available data). For CYP2D6, the IonS5-PharmacoScan concordance was 94% for a range of variants tested apart from those with at least one extra copy of a CYP2D6 gene (occurring at a frequency of 3.8%, 33/853), or those with substantial sequence derived from pseudogene, known as hybrids (3%, 26/853). ConclusionsInter-platform concordance for CYP2C19 was high, and, moreover, the Ion S5 and PharmacoScan data were 100% concordant with that from a TaqMan CYP2C19*2 assay. We have also demonstrated feasibility of using an NGS platform for genotyping CYP2D6 and CYP2C19, with automated data interpretation methodology. This points the way to a method of making CYP2D6 and CYP2C19 genotyping more readily accessible.

genetics↗