How to analyze mitochondrial morphology in healthy cells and apoptotic cells in Caenorhabditis elegans

Polygonum multiflorum Thunb extract extended the lifespan and healthspan of Caenorhabditis elegans via DAF-16/SIR-2.1/SKN-1

Polygonum multiflorum Thunb (PMT), as a traditional Chinese herbal medicine, has been widely used in the prevention and treatment of aging-related diseases, including Alzheimer's disease, Parkinson's disease, hyperlipidemia, atherosclerosis and inflammation. However, the effect of PMT on the lifespan and its molecular mechanisms are still unclear. Here we found that 60% ethanol refined fraction (PMT-E) of Polygonum multiflorum Thunb at 50 μg mL^-1, which contained two main bioactive compounds, 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG) and emodin-8-O-β-D-glucoside (EG), could significantly increase the mean lifespan by 19.82%, delay the age-related decline of phenotypes, enhance stress resistance and reduce ROS accumulation in Caenorhabditis elegans. Moreover, we also found that the mitochondrial membrane potential (ΔΨ) and ATP content of worms treated with 50 μg mL^-1 PMT-E were obviously improved. Further mechanistic studies revealed that DAF-16, SIR-2.1 and SKN-1 transcription factors were required for PMT-E-mediated lifespan extension. Finally, we found that PMT-E could significantly inhibit the toxicity induced by β-amyloid (Aβ) in Aβ transgenic worms. Altogether, these findings laid the foundation for the use of Polygonum multiflorum Thunb to treat aging and age-related diseases.

Evaluations of Environmental Pollutant-Induced Mitochondrial Toxicity Using Caenorhabditis elegans as a Model System

Environmental pollutants inevitably exert adverse effects on humans and other species. Quick identification and in-depth characterization of the pollutants are requisite objectives for clinicians and environmental health scientists. The nematode Caenorhabditis elegans has been utilized as a model organism for toxicity evaluation of environmental pollutants, due to its transparency, short lifespan, entire genome sequencing, and economical characteristics. However, few researchers have systematically addressed mitochondrial toxicity in response to toxicants, despite the critical role mitochondria play in energy production and respiration, as well as the generation of reactive oxygen species. Mitochondria are vulnerable to environmental pollutants, and their dysfunction contributes to cellular damage and toxicity in plethora of diseases. Here, we describe methods in step-by-step for mitochondrial toxicity evaluation in response to pollutants, including exposure of C. elegans to toxicants, mitochondrial ROS detection, mitochondrial morphology analysis, mitochondrial function analysis, such as ATP production and oxygen consumption, and gene expression studies, with the application of corresponding genetically modified strains.

Caenorhabditis elegans ATPase inhibitor factor 1 (IF1) MAI-2 preserves the mitochondrial membrane potential (Δψm) and is important to induce germ cell apoptosis

When the electrochemical proton gradient is disrupted in the mitochondria, IF1 (Inhibitor Factor-1) inhibits the reverse hydrolytic activity of the F1Fo-ATP synthase, thereby allowing cells to conserve ATP at the expense of losing the mitochondrial membrane potential (Δψm). The function of IF1 has been studied mainly in different cell lines, but these studies have generated contrasting results, which have not been helpful to understand the real role of this protein in a whole organism. In this work, we studied IF1 function in Caenorhabditis elegans to understand IF1´s role in vivo. C. elegans has two inhibitor proteins of the F1Fo-ATPase, MAI-1 and MAI-2. To determine their protein localization in C. elegans, we generated translational reporters and found that MAI-2 is expressed ubiquitously in the mitochondria; conversely, MAI-1 was found in the cytoplasm and nuclei of certain tissues. By CRISPR/Cas9 genome editing, we generated mai-2 mutant alleles. Here, we showed that mai-2 mutant animals have normal progeny, embryonic development and lifespan. Contrasting with the results previously obtained in cell lines, we found no evident defects in the mitochondrial network, dimer/monomer ATP synthase ratio, ATP concentration or respiration. Our results suggest that some of the roles previously attributed to IF1 in cell lines could not reflect the function of this protein in a whole organism and could be attributed to specific cell lines or methods used to silence, knockout or overexpress this protein. However, we did observe that animals lacking IF1 had an enhanced Δψm and lower physiological germ cell apoptosis. Importantly, we found that mai-2 mutant animals must be under stress to observe the role of IF1. Accordingly, we observed that mai-2 mutant animals were more sensitive to heat shock, oxidative stress and electron transport chain blockade. Furthermore, we observed that IF1 is important to induce germ cell apoptosis under certain types of stress. Here, we propose that MAI-2 might play a role in apoptosis by regulating Δψm. Additionally, we suggest that IF1 function is mainly observed under stress and that, under physiological conditions, this protein does not play an essential role.

New Imaging Tools to Analyze Mitochondrial Morphology in Caenorhabditis elegans

Mitochondria are highly dynamic organelles that constantly fuse and divide. This process is essential as several neurodegenerative diseases have been associated with defects in mitochondrial fusion or fission. Several tools have been developed over the years to visualize mitochondria in organisms such as Caenorhabditis elegans. Combining these tools with the powerful genetics of C. elegans has led to the discovery of new regulators of mitochondrial morphology. In this chapter, we present additional tools to further characterize mitochondrial morphology as well as regulators of mitochondrial morphology. Specifically, we introduce a photoactivatable mitoGFP (PAmitoGFP) that allows to investigate the connectivity of complex mitochondrial networks. In addition, we describe an immunostaining protocol that enables localization studies of these newly identified regulators of mitochondrial morphology.

Exercise in an electrotactic flow chamber ameliorates age-related degeneration in Caenorhabditis elegans

Degeneration is a senescence process that occurs in all living organisms. Although tremendous efforts have been exerted to alleviate this degenerative tendency, minimal progress has been achieved to date. The nematode, Caenorhabditis elegans (C. elegans), which shares over 60% genetic similarities with humans, is a model animal that is commonly used in studies on genetics, neuroscience, and molecular gerontology. However, studying the effect of exercise on C. elegans is difficult because of its small size unlike larger animals. To this end, we fabricated a flow chamber, called “worm treadmill,” to drive worms to exercise through swimming. In the device, the worms were oriented by electrotaxis on demand. After the exercise treatment, the lifespan, lipofuscin, reproductive capacity, and locomotive power of the worms were analyzed. The wild-type and the Alzheimer’s disease model strains were utilized in the assessment. Although degeneration remained irreversible, both exercise-treated strains indicated an improved tendency compared with their control counterparts. Furthermore, low oxidative stress and lipofuscin accumulation were also observed among the exercise-treated worms. We conjecture that escalated antioxidant enzymes imparted the worms with an extra capacity to scavenge excessive oxidative stress from their bodies, which alleviated the adverse effects of degeneration. Our study highlights the significance of exercise in degeneration from the perspective of the simple life form, C. elegans.