A tRNA processing enzyme is a key regulator of the mitochondrial unfolded protein response

CYP14 family in Caenorhabditis elegans: Mitochondrial function, detoxification, and lifespan

CYP-14 members of the Caenorhabditis elegans (C. elegans) Cytochrome P450 (CYP) enzyme family, plays important roles in mitochondrial dysfunction, detoxification, lipid metabolism, defense and lifespan regulation. The review identifies CYP-14 members: cyp-14A1, cyp-14A2, cyp-14A3, cyp-14A4, cyp-14A5 and their homology with human CYP families. Despite limited studies on C. elegans cyp-14 members, the findings unraveled their complex crosstalk between mitochondrial stress, detoxification mechanisms, and lifespan regulation, emphasizing the complexity of these interconnected pathways as well as how their regulation depends on environmental cues changes including pH, nutrients, ROS and chemical stressors. The review underscores the translational relevance to human health, shedding light on potential human homologues and their implications in age-related, metabolic and respiratory diseases. Among other genes, cyp-14A2 and cyp-14A4 predominate the mitochondrial function, heat resistance, lipid metabolism, detoxification and lifespan pathways. In conclusion, these insights pave the way for future research, offering promising avenues for therapeutic interventions targeting CYP-14 activity to address age-related diseases and promote healthy aging.

A viable hypomorphic mutation in the mitochondrial ribosome subunit, MRPS-31, exhibits mitochondrial dysfunction in C. elegans

The mitochondrial ribosome (mitoribosome) translates mitochondrial genome encoded proteins essential for cellular energy production. Given this critical role, defects in the mitoribosome can cause mitochondrial stress and manifest as multisystemic diseases. In a screen for unique activators of the mitochondrial unfolded protein response (UPR mt ) in Caenorhabditis elegans , we recovered a strain harboring a missense mutation in the gene encoding mitochondrial ribosome protein S31 ( MRPS-31 )-a component of the mitoribosome small subunit. Herein, we confirm causality of the mrps-31 allele and characterize its induction of UPR mt and impact on organismal development, providing a valuable model for further study of the mitoribosome.

Decreased ATF5 level contributes to improved mitochondrial function in oocytes exposed to vitrification stress

Background

Mitochondrial unfolded protein response (mtUPR) plays an essential role in the response of mitochondria to stress-induced damage. Activating of transcription factor 5 (ATF5) can help to sustain mitochondrial function and regulate organelle recovery under mitochondrial stress. Vitrification is a stressor that disrupts mitochondrial activity and cell homeostasis. However, little is known about the function of ATF5 in response to the extreme biophysical and chemical stresses during oocyte vitrification.

Methods

The expression of ATF5 and mtUPR biomarkers were measured in fresh and vitrified oocytes. Subsequently, oocytes with ATF5 deficiency were constructed by siRNA microinjection, and the function of ATF5 in mitochondrial function and oocyte development were analyzed in vitrified oocytes. Furthermore, transcriptome analysis was performed to uncover the molecular network regulated by ATF5 in response to oocyte vitrification.

Results

In the present study, the mitochondrial membrane potential and ATP levels were decreased in ATF5 knockdown oocytes, in line with the phenotypes observed in vitrified oocytes. In addition, ATF5 knockdown resulted in decreased mitochondrial temperature, reduced unfolded protein levels, abnormal mitochondrial dynamics (fusion and fission), and increased autophagy. Subsequent experiments indicated that mtUPR was suppressed in oocytes with ATF5 knockdown. Interestingly, ATF5 was aberrantly upregulated in oocytes exposed to vitrification stress. Reduced ATF5 expression to a homeostatic level in vitrified oocytes led to accumulated unfolded protein levels and increased mitochondrial membrane potential. Moreover, increased mitochondrial dynamics and an increased germinal vesicle breakdown (GVBD) rate were detected after in vitro maturation. Transcriptome analysis revealed that ATF5 is involved in the vitrification stress response, and ATF5 regulated the in vitro maturation potential in vitrified oocytes through the cAMP-PKA and PI3K/AKT pathways.

Discussion

Our findings indicate that mtUPR was initiated in response to vitrification stimuli, and downregulated ATF5 level to a homeostatic state contributes to improved mitochondrial function in oocytes exposed to vitrification stress. Our results highlight the crucial role of ATF5 in the regulation of mitochondrial function in vitrified oocytes through mediating mtUPR.

A bird's eye view of mitochondrial unfolded protein response in cancer: mechanisms, progression and further applications

Mitochondria are essential organelles that play critical roles in energy metabolism, apoptosis and various cellular processes. Accumulating evidence suggests that mitochondria are also involved in cancer development and progression. The mitochondrial unfolded protein response (UPRmt) is a complex cellular process that is activated when the protein-folding capacity of the mitochondria is overwhelmed. The core machinery of UPRmt includes upstream regulatory factors, mitochondrial chaperones and proteases. These components work together to eliminate misfolded proteins, increase protein-folding capacity, and restore mitochondrial function. Recent studies have shown that UPRmt is dysregulated in various cancers and contributes to tumor initiation, growth, metastasis, and therapeutic resistance. Considering the pivotal role of the UPRmt in oncogenesis, numerous compounds and synthetic drugs targeting UPRmt-related components induce cancer cell death and suppress tumor growth. In this review, we comprehensively summarize recent studies on the molecular mechanisms of UPRmt activation in C. elegans and mammals and elucidate the conceptual framework, functional aspects, and implications of the UPRmt for cancer therapy. In summary, we paint a developmental landscape of the UPRmt in different types of cancer and offer valuable insights for the development of novel cancer treatment strategies by targeting the UPRmt.

Germline status and micronutrient availability regulate a somatic mitochondrial quality control pathway via short-chain fatty acid metabolism

Reproductive status, such as pregnancy and menopause in women, profoundly influences metabolism of the body. Mitochondria likely orchestrate many of these metabolic changes. However, the influence of reproductive status on somatic mitochondria and the underlying mechanisms remain largely unexplored. We demonstrate that reproductive signals modulate mitochondria in the Caenorhabditis elegans soma. We show that the germline acts via an RNA endonuclease, HOE-1, which despite its housekeeping role in tRNA maturation, selectively regulates the mitochondrial unfolded protein response (UPRmt). Mechanistically, we uncover a fatty acid metabolism pathway acting upstream of HOE-1 to convey germline status. Furthermore, we link vitamin B12's dietary intake to the germline's regulatory impact on HOE-1-driven UPRmt. Combined, our study uncovers a germline-somatic mitochondrial connection, reveals the underlying mechanism, and highlights the importance of micronutrients in modulating this connection. Our findings provide insights into the interplay between reproductive biology and metabolic regulation.

A role for N6-methyldeoxyadenosine in C. elegans mitochondrial genome regulation

Epigenetic modifications provide powerful means for transmitting information from parent to progeny. As a maternally inherited genome that encodes essential components of the electron transport chain, the mitochondrial genome (mtDNA) is ideally positioned to serve as a conduit for the transgenerational transmission of metabolic information. Here, we provide evidence that mtDNA of C. elegans contains the epigenetic mark N6-methyldeoxyadenosine (6mA). Bioinformatic analysis of SMRT sequencing data and methylated DNA IP sequencing data reveal that C. elegans mtDNA is methylated at high levels in a site-specific manner. We further confirmed that mtDNA contains 6mA by leveraging highly specific anti-6mA antibodies. Additionally, we find that mtDNA methylation is dynamically regulated in response to antimycin, a mitochondrial stressor. Further, 6mA is increased in nmad-1 mutants and is accompanied by a significant decrease in mtDNA copy number. Our discovery paves the way for future studies to investigate the regulation and inheritance of mitochondrial epigenetics.

The role of tRNA-derived small RNAs in aging

Aging is characterized by a gradual decline in biological functions, leading to the increased probability of diseases and deaths in organisms. Previous studies have identified biological factors that modulate aging and lifespan, including non-coding RNAs (ncRNAs). Here, we review the relationship between aging and tRNA-derived small RNAs (tsRNAs), ncRNAs that are generated from the cleavage of tRNAs. We describe age-dependent changes in tsRNA levels and their functions in age-related diseases, such as cancer and neurodegenerative diseases. We also discuss the association of tsRNAs with aging-regulating processes, including mitochondrial respiration and reduced mRNA translation. We cover recent findings regarding the potential roles of tsRNAs in cellular senescence, a major cause of organismal aging. Overall, our review will provide useful information for understanding the roles of tsRNAs in aging and age-associated diseases. [BMB Reports 2023; 56(2): 49-55].

The role of tRNA-derived small RNAs in aging

Aging is characterized by a gradual decline in biological functions, leading to the increased probability of diseases and deaths in organisms. Previous studies have identified biological factors that modulate aging and lifespan, including non-coding RNAs (ncRNAs). Here, we review the relationship between aging and tRNA-derived small RNAs (tsRNAs), ncRNAs that are generated from the cleavage of tRNAs. We describe age-dependent changes in tsRNA levels and their functions in age-related diseases, such as cancer and neurodegenerative diseases. We also discuss the association of tsRNAs with aging-regulating processes, including mitochondrial respiration and reduced mRNA translation. We cover recent findings regarding the potential roles of tsRNAs in cellular senescence, a major cause of organismal aging. Overall, our review will provide useful information for understanding the roles of tsRNAs in aging and age-associated diseases. [BMB Reports 2023; 56(2): 49-55].