Some Liked It Hot: A Hypothesis Regarding Establishment of the Proto-Mitochondrial Endosymbiont During Eukaryogenesis

Tracing the evolutionary pathway: on the origin of mitochondria and eukaryogenesis

The mito-early hypothesis posits that mitochondrial integration was a key driver in the evolution of defining eukaryotic characteristics (DECs). Building on previous work that identified endosymbiotic selective pressures as central to eukaryotic cell evolution, this study examines how endosymbiotic gene transfer (EGT) and the resulting genomic and bioenergetic constraints shaped mitochondrial protein import systems. These systems were crucial for maintaining cellular function in early eukaryotes and facilitated their subsequent diversification. A primary focus is the co-evolution of mitochondrial import mechanisms and eukaryotic endomembrane complexity. Specifically, I investigate how the necessity for nuclear-encoded mitochondrial protein import drove the adaptation of bacterial secretion components, alongside eukaryotic innovations, to refine translocation pathways. Beyond enabling bioenergetic expansion, mitochondrial endosymbiosis played a fundamental role in the emergence of compartmentalisation and cellular complexity in LECA, driving the evolution of organellar networks. By integrating genomic, structural and phylogenetic evidence, this study aimed to contribute to the mito-early framework, clarifying the mechanisms that linked mitochondrial acquisition to the origin of eukaryotic cells.

Mitochondrial Dysfunction in Endothelial Cells: A Key Driver of Organ Disorders and Aging

Mitochondria are of great importance in cell biology since they are major sites of adenosine triphosphate (ATP) production and are widely involved in different cellular pathways involved in the response to stress. During ATP production, reactive oxygen species (ROS) can be produced. While a small amount of ROS may be important for the regulation of physiological processes, at elevated levels they can turn into harmful agents leading to cellular damage. From a pathological perspective, it could be particularly interesting to focus on mitochondrial function in endothelial cells since they may be involved in the development of aging and in the onset of different diseases, including renal, cardio-metabolic, liver and neurodegenerative ones. However, to date, there are no surveys which address the above issues. To fill this gap, it may be valuable to collect recent findings about the role of mitochondria in the regulation of endothelial function, not only to increase knowledge about it but also for clinical applications. Here, we overview the most recent knowledge about the above issues in the view of characterizing the role of mitochondria in endothelial cells as an innovative potential target for the prevention of aging, as well as the treatment of the above pathological conditions.

Mitochondria: great balls of fire

Recent experimental studies indicate that mitochondria in mammalian cells are maintained at temperatures of at least 50 °C. While acknowledging the limitations of current experimental methods and their interpretation, we here consider the ramifications of this finding for cellular functions and for evolution. We consider whether mitochondria as heat-producing organelles had a role in the origin of eukaryotes and in the emergence of homeotherms. The homeostatic responses of mitochondrial temperature to externally applied heat imply the existence of a molecular heat-sensing system in mitochondria. While current findings indicate high temperatures for the innermost compartments of mitochondria, those of the mitochondrial surface and of the immediately surrounding cytosol remain to be determined. We ask whether some aspects of mitochondrial dynamics and motility could reflect changes in the supply and demand for mitochondrial heat, and whether mitochondrial heat production could be a factor in diseases and immunity.

Wolbachia infection negatively impacts Drosophila simulans heat tolerance in a strain- and trait-specific manner

The susceptibility of insects to rising temperatures has largely been measured by their ability to survive thermal extremes. However, the capacity for maternally inherited endosymbionts to influence insect heat tolerance has been overlooked. Further, while some studies have addressed the impact of heat on traits like fertility, which can decline at temperatures below lethal thermal limits, none have considered the impact of endosymbionts. Here, we assess the impact of three Wolbachia strains (wRi, wAu and wNo) on the survival and fertility of Drosophila simulans exposed to heat stress during development or as adults. The effect of Wolbachia infection on heat tolerance was generally small and trait/strain specific. Only the wNo infection significantly reduced the survival of adult males after a heat shock. When exposed to fluctuating heat stress during development, the wRi and wAu strains reduced egg-to-adult survival but only the wNo infection reduced male fertility. Wolbachia densities of all three strains decreased under developmental heat stress, but reductions occurred at temperatures above those that reduced host fertility. These findings emphasize the necessity to account for endosymbionts and their effect on both survival and fertility when investigating insect responses to heat stress.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

The multiple facets of mitochondrial regulations controlling cellular thermogenesis

Understanding temperature production and regulation in endotherm organisms becomes a crucial challenge facing the increased frequency and intensity of heat strokes related to global warming. Mitochondria, located at the crossroad of metabolism, respiration, Ca2+ homeostasis, and apoptosis, were recently proposed to further act as cellular radiators, with an estimated inner temperature reaching 50 °C in common cell lines. This inner thermogenesis might be further exacerbated in organs devoted to produce consistent efforts as muscles, or heat as brown adipose tissue, in response to acute solicitations. Consequently, pathways promoting respiratory chain uncoupling and mitochondrial activity, such as Ca2+ fluxes, uncoupling proteins, futile cycling, and substrate supplies, provide the main processes controlling heat production and cell temperature. The mitochondrial thermogenesis might be further amplified by cytoplasmic mechanisms promoting the over-consumption of ATP pools. Considering these new thermic paradigms, we discuss here all conventional wisdoms linking mitochondrial functions to cellular thermogenesis in different physiological conditions.

Mitochondrial iron-sulfur clusters: Structure, function, and an emerging role in vascular biology

Iron-sulfur (Fe-S) clusters are essential cofactors most commonly known for their role mediating electron transfer within the mitochondrial respiratory chain. The Fe-S cluster pathways that function within the respiratory complexes are highly conserved between bacteria and the mitochondria of eukaryotic cells. Within the electron transport chain, Fe-S clusters play a critical role in transporting electrons through Complexes I, II and III to cytochrome c, before subsequent transfer to molecular oxygen. Fe-S clusters are also among the binding sites of classical mitochondrial inhibitors, such as rotenone, and play an important role in the production of mitochondrial reactive oxygen species (ROS). Mitochondrial Fe-S clusters also play a critical role in the pathogenesis of disease. High levels of ROS produced at these sites can cause cell injury or death, however, when produced at low levels can serve as signaling molecules. For example, Ndufs2, a Complex I subunit containing an Fe-S center, N2, has recently been identified as a redox-sensitive oxygen sensor, mediating homeostatic oxygen-sensing in the pulmonary vasculature and carotid body. Fe-S clusters are emerging as transcriptionally-regulated mediators in disease and play a crucial role in normal physiology, offering potential new therapeutic targets for diseases including malaria, diabetes, and cancer.

The complete mitochondrial genome of medicinal fungus Taiwanofungus camphoratus reveals gene rearrangements and intron dynamics of Polyporales

Taiwanofungus camphoratus is a highly valued medicinal mushroom that is endemic to Taiwan, China. In the present study, the mitogenome of T. camphoratus was assembled and compared with other published Polyporales mitogenomes. The T. camphoratus mitogenome was composed of circular DNA molecules, with a total size of 114,922 bp. Genome collinearity analysis revealed large-scale gene rearrangements between the mitogenomes of Polyporales, and T. camphoratus contained a unique gene order. The number and classes of introns were highly variable in 12 Polyporales species we examined, which proved that numerous intron loss or gain events occurred in the evolution of Polyporales. The Ka/Ks values for most core protein coding genes in Polyporales species were less than 1, indicating that these genes were subject to purifying selection. However, the rps3 gene was found under positive or relaxed selection between some Polyporales species. Phylogenetic analysis based on the combined mitochondrial gene set obtained a well-supported topology, and T. camphoratus was identified as a sister species to Laetiporus sulphureus. This study served as the first report on the mitogenome in the Taiwanofungus genus, which will provide a basis for understanding the phylogeny and evolution of this important fungus.

Endosymbiosis before eukaryotes: mitochondrial establishment in protoeukaryotes

Endosymbiosis and organellogenesis are virtually unknown among prokaryotes. The single presumed example is the endosymbiogenetic origin of mitochondria, which is hidden behind the event horizon of the last eukaryotic common ancestor. While eukaryotes are monophyletic, it is unlikely that during billions of years, there were no other prokaryote-prokaryote endosymbioses as symbiosis is extremely common among prokaryotes, e.g., in biofilms. Therefore, it is even more precarious to draw conclusions about potentially existing (or once existing) prokaryotic endosymbioses based on a single example. It is yet unknown if the bacterial endosymbiont was captured by a prokaryote or by a (proto-)eukaryote, and if the process of internalization was parasitic infection, slow engulfment, or phagocytosis. In this review, we accordingly explore multiple mechanisms and processes that could drive the evolution of unicellular microbial symbioses with a special attention to prokaryote-prokaryote interactions and to the mitochondrion, possibly the single prokaryotic endosymbiosis that turned out to be a major evolutionary transition. We investigate the ecology and evolutionary stability of inter-species microbial interactions based on dependence, physical proximity, cost-benefit budget, and the types of benefits, investments, and controls. We identify challenges that had to be conquered for the mitochondrial host to establish a stable eukaryotic lineage. Any assumption about the initial interaction of the mitochondrial ancestor and its contemporary host based solely on their modern relationship is rather perilous. As a result, we warn against assuming an initial mutually beneficial interaction based on modern mitochondria-host cooperation. This assumption is twice fallacious: (i) endosymbioses are known to evolve from exploitative interactions and (ii) cooperativity does not necessarily lead to stable mutualism. We point out that the lack of evidence so far on the evolution of endosymbiosis from mutual syntrophy supports the idea that mitochondria emerged from an exploitative (parasitic or phagotrophic) interaction rather than from syntrophy.

Mitochondria Are Fundamental for the Emergence of Metazoans: On Metabolism, Genomic Regulation, and the Birth of Complex Organisms

Out of many intracellular bacteria, only the mitochondria and chloroplasts abandoned their independence billions of years ago and became endosymbionts within the host eukaryotic cell. Consequently, one cannot grow eukaryotic cells without their mitochondria, and the mitochondria cannot divide outside of the cell, thus reflecting interdependence. Here, we argue that such interdependence underlies the fundamental role of mitochondrial activities in the emergence of metazoans. Several lines of evidence support our hypothesis: (a) Differentiation and embryogenesis rely on mitochondrial function; (b) mitochondrial metabolites are primary precursors for epigenetic modifications (such as methyl and acetyl), which are critical for chromatin remodeling and gene expression, particularly during differentiation and embryogenesis; and (c) mitonuclear coregulation adapted to accommodate both housekeeping and tissue-dependent metabolic needs. We discuss the evolution of the unique mitochondrial genetic system, mitochondrial metabolites, mitonuclear coregulation, and their critical roles in the emergence of metazoans and in human disorders.

Feeling the Heat: Evolutionary and Microbial Basis for the Analgesic Mechanisms of Photobiomodulation Therapy

Background: The clinical therapeutic benefits of Photobiomodulation (PBM) therapy have been well established in many clinical scenarios. However, we are far from having developed a complete understanding of the underlying mechanisms of photon-biological tissue interactions. Concurrent to ongoing PBM studies, there are several parallel fields with evidences from cell and tissue physiology such as evolutionary biology, photobiology, and microbiology among others. Objective: This review is focused on extrapolating evidences from an expanded range of studies that may contribute to a better understanding of PBM mechanisms especially focusing on analgesia. Further, the choice of a PBM device source and relevant dosimetry with regards to specific mechanisms are discussed to enable broader clinical use of PBM therapies. Materials and methods: This discussion article is referenced from an expanded range of peer reviewed publications, including literature associated with evolutionary biology, microbiology, oncology, and photo-optical imaging technology, amongst others. Results and discussion: Materials drawn from many disparate disciplines is described. By inference from the current evidence base, a novel theory is offered to partially explain the cellular basis of PBM-induced analgesia. It is proposed that this may involve the activity of a class of transmembrane proteins known as uncoupling proteins. Furthermore, it is proposed that this may activate the heat stress protein response and that intracellur microthermal inclines may be of significance in PBM analgesia. It is suggested that the PBM dose response as a simple binary model of PBM effects as represented by the Arndt-Schulz law is clinically less useful than a multiphasic biological response. Finally, comments are made concerning the nature of photon to tissue interaction that can have significance in regard to the effective choice and delivery of dose to clinical target. Conclusions: It is suggested that a re-evaluation of phototransduction pathways may lead to an improvement in outcome in phototheraphy. An enhanced knowledge of safe parameters and a better knowledge of the mechanics of action at target level will permit more reliable and predictable clinical gain and assist the acceptance of PBM therapy within the wider medical community.

Characterization and phylogenetic analysis of the complete mitochondrial genome of the medicinal fungus Laetiporus sulphureus

The medicinal fungus Laetiporus sulphureus is widely distributed worldwide. To screen for molecular markers potentially useful for phylogenetic analyses of this species and related species, the mitochondrial genome of L. sulphureus was sequenced and assembled. The complete circular mitochondrial genome was 101,111 bp long, and contained 38 protein-coding genes (PCGs), 2 rRNA genes, and 25 tRNA genes. Our BLAST search aligned about 6.1 kb between the mitochondrial and nuclear genomes of L. sulphureus, indicative of possible gene transfer events. Both the GC and AT skews in the L. sulphureus mitogenome were negative, in contrast to the other seven Polyporales species tested. Of the 15 PCGs conserved across the seven species of Polyporales, the lengths of 11 were unique in the L. sulphureus mitogenome. The Ka/Ks of these 15 PCGs were all less than 1, indicating that PCGs were subject to purifying selection. Our phylogenetic analysis showed that three single genes (cox1, cob, and rnl) were potentially useful as molecular markers. This study is the first publication of a mitochondrial genome in the family Laetiporaceae, and will facilitate the study of population genetics and evolution in L. sulphureus and other species in this family.