Biology subjects

Tjahjono, E.

Publications and source records attributed to Tjahjono, E..

4 recordsLinked to original sources

bioRxiv2022

Dietary derived Vitamin B12 protects the nematode Caenorhabditis elegans from thiol reducing agents.

We describe a novel SAM methyl transferase in the nematode Caenorhabditis elegans that is upregulated by thiol reducing agents and hydrogen sulfide with expression controlled by the hypoxia inducible factor pathway. This methyl transferase, RIPS-1, is expressed in the gut and hypodermis of this nematode with homologues found in a small subset of eukaryotes and bacteria, many of which can adapt to fluctuations in environmental oxygen levels. We identified RIPS-1 through forward genetic screens as the only gene that when mutated allowed worms to survive normally lethal concentrations of thiol reducing agents such as dithiothreitol (DTT) and {beta}-mercaptoethanol. The RIPS-1 methyl transferase is an important player in the methionine cycle and its activation consumes methionine in a methionine synthetase and vitamin B12-dependant manner. This requirement limits the availability of vitamin B12 in the mitochondrion. Mitochondrial involvement was also established through a targeted enhancer screen that identified methylmalonyl-CoA epimerase as a strong genetic enhancer of RIPS-1 mutant resistance to DTT. Toxicity associated with thiol reducing agent exposure can be overcome in C. elegans by adding methionine, loss of RIPS-1, or by addition of excess vitamin B12. This work highlights the central importance of dietary vitamin B12 in normal metabolic processes in C. elegans and defines a new role in countering reductive stress

biochemistry↗

bioRxiv2022

A Novel Caenorhabditis elegans Gene Network Uncovers Mechanisms of Mitochondrial Maintenance

Mitochondria play key roles in cellular health and metabolism and are a critical determinant of the activation of multiple cell death processes. Although several pathways for regulating and re-establishing mitochondrial homeostasis have been identified within the past twenty years, large gaps remain in our understanding of how cells keep mitochondria healthy. To address this limitation, have developed a network of genes that underlie mitochondrial health. We began by compiling a list of frequently mutated genes using publicly available data from multiple human cancer cell lines. RNAi was used to disrupt orthologous genes in the model organism Caenorhabditis elegans in a series of assays to evaluate these genes ability to support mitochondrial health, as evidenced by precocious activation of mitochondrial autophagy and sensitivity to acute mitochondrial damage. Iterative screening of ~1000 genes yielded a network of 139 genes showing significant connectivity. Functional validation of a panel of genes from the network indicated that disruption of each gene triggered at least one phenotype consistent with mitochondrial dysfunction, including increased fragmentation of the mitochondrial network, abnormal steady-state levels of ATP, NADH, or ROS, and altered oxygen consumption. Importantly, RNAi-mediated knockdown of these genes often exacerbated -synuclein aggregation in a C. elegans model of Parkinsons disease, indicating significant changes to cellular health. Additionally, human orthologs of the final mitochondrial health gene network showed enrichment for roles in a number of human disorders identified in the OMIM database. This gene network provides a foundation for identifying new mechanisms that support mitochondrial and cellular homeostasis.

genetics↗

bioRxiv2021

Small Molecule Stabilization of PINK-1/PINK1 Improves Neurodegenerative Disease

Macroautophagic recycling of dysfunctional mitochondria, known as mitophagy, is essential for mitochondrial homeostasis and cell viability. Accumulation of defective mitochondria and impaired mitophagy have been widely implicated in many neurodegenerative diseases, and loss-of-function mutations of two regulators of mitophagy, PINK1 and Parkin, are amongst the most common causes of recessive Parkinsons disease. Activation of mitophagy via pharmacological treatments may be a feasible approach for combating neurodegeneration. In this effort, we screened [~]45,000 small molecules for the ability to activate mitophagy. A high-throughput, whole-organism, phenotypic screen was conducted by monitoring stabilization of PINK-1/PINK1, a key event in mitophagy activation, in a Caenorhabditis elegans strain carrying a Ppink-1::PINK-1::GFP reporter. We obtained eight hits that induced mitophagy, as evidenced by increased mitochondrial fragmentation and autophagosome formation. Several of the compounds also reduced ATP production, oxygen consumption, mitochondrial mass, and/or mitochondrial membrane potential. Importantly, we found that treatment with two compounds, which we named PS83 and PS106 (more commonly known as sertraline) reduced neurodegenerative disease phenotypes (including delayed paralysis in a C. elegans Alzheimers model) in a PINK-1/PINK1-dependent manner. This report presents a promising step toward the identification of compounds that will stimulate mitochondrial turnover.

cell biology↗

bioRxiv2021

Box C/D Small Nucleolar Ribonucleoproteins Regulate Mitochondrial Surveillance and Innate Immunity

Monitoring of mitochondrial functions is crucial for organismal survival. This task is performed by mitochondrial surveillance or quality control pathways, which are activated by signals originating from mitochondria and relayed to the nucleus (retrograde response) to start the transcription of protective genes. In Caenorhabditis elegans, several systems exist, including the UPRmt, MAPKmt, and the ESRE pathway. These pathways are highly conserved and their loss results in compromised survival following mitochondrial stress. In this study, we found a novel interaction between the box C/D snoRNA core proteins (snoRNPs) and mitochondrial surveillance and innate immunity pathways. We showed that C/D snoRNPs are required for the full expressions of UPRmt and ESRE upon stress. Meanwhile, we found that the loss of C/D snoRNPs increased immune responses. Understanding the "molecular switch" mechanisms of interplay between these pathways may be important for understanding of multifactorial processes, including response to infection or aging.

cell biology↗