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The first codon of the Gene encoding has a CAG repeat expansion that causes HD. Between SCA6 and SCA8, the number of CAG repeats that cause sickness ranges between 21 and 55. (SCA3). In either case, the CAG repeat expansion is more than likely responsible for the sickness, regardless of the patient's ancestry.. Multiple lines of evidence pointed to mitochondrial dysfunction in poly aetiology. A hallmark of HD is mitochondrial fragmentation, occurring in both transgenic HD cell lines and human HD cells. Other polyQ disorders with mitochondrial fragmentation include SCA3, SCA7, and SBMA. For mitochondrial fragmentation, CAG repeat expansion is sufficient. The mitochondrial fission protein DRP1 has been the focus of several studies in HD models in an attempt to minimize mitochondrial disintegration. Contrary to popular belief, genetic or pharmacological interventions that directly or indirectly limit DRP1 activity have improved HD characteristics. DRP-1 deletion in an HD model was detrimental, but RNAi knockdown of the same protein had mixed results.

Methods

NGM plates were inoculated with OP50 bacterium, and many strains were employed and kept at 20°C. PCR genotyping and fluorescence microscopy observations were used to confirm all crossovers. (Traa et al., 2021).

Confocal anatomical and molecular imaging

Mitochondrial RFP-specific specimen were used for the experiment because they expressed it exclusively in the muscles of their body walls. Pixel pickers were utilised to choose a variety of control minor fps. After adding the threshold mask, they used Nikon Elements AR's measure objects tool to get the measurements needed. Prism was used for all other calculations.

Oxygen consumption

BOC was measured using the Seahorse XFe96 analyser. They were washing adult synchronised worms in M9 buffer. It was necessary to normalise the respiration rate for each well based on the number of worms contained there. To establish a link between the rate of oxidative phosphorylation and the phenotypes they were studying, they decided to measure the oxygen intake of each worm.

ATP production

The ATP kit utilised luminescence to measure ATP levels. Age synchronisation was accomplished by limiting worm laying to 200 at a time. Molecular Probes' ATP determination kit collected the supernatant and quantified it.

Rate of movement

Video-tracking and computer analysis were used to measure the thrashing rate in fluids to determine the impacts of drop-1.

Day 1 subjects were segregated at the L4 stage before testing. RNAi clones were tested to see whether they affected animal development and if they did, the animals were grown on empty vectors before being given the clones. Images were captured with a Zyla Andor sCM05 camera and a Nikon Eclipse Ti microscope. 

Discussion

To maintain cell function, mitochondrial fission and fusion must be balanced. Mitochondrial connectivity fragmentation, whether it occurred as a result of major or minor alterations in mitochondrial dynamics, was often connected to degenerative illnesses. It was shown that in healthy cells, mitochondria generated a linked system with a greater mean degree, immense cluster and division lengths, clusters and swirls, than in cells with nine distinct diseases after analysing photos of mitochondrial networks from several prior experimental investigations.  The author created a mitochondrial model network based on these illnesses that included these differences. During transient fusion, a pair of mitochondria nearby fused for a brief period (45 s on average) before dissociating and returning to their original topologies.  In all, nine conditions fall into two groups. Mitochondrial lateral contact caused mitochondrial fusion to be decreased and fission enhanced in the cells of people with Alzheimer's disease, heart disease, diabetes/cancer, and acute kidney impairment. Because of the reduced fusing caused by longitudinal contact, the mitochondrial network became more fractious. The form and position of mitochondria fragmentation determined how fragmentation affects cell function because of mitochondrial disintegration and fusion in microscopic detail. 

Multiple animal models have been developed to study the aetiology of HD and other polyQ illnesses since discovering the genes that cause these illnesses. HD and polyQ contagiousness had been studied in C. elegans models. To examine mitochondrial dynamics, C. elegance’s translucent nature made it possible to see mitochondrial morphology in live organisms linked to overall phenotypes.

Expansion of CAG Repeats Affects the Morphology and Function of Neuronal Mitochondrion.

A significant amount of neuropathology can be found in patients with HD and related polyQ disorders. To get a better understanding of mitochondrial structure in cells, the author developed many new strains. When the concentration of CAG in Neur-67Q neurons grew, mitochondria in the peripheral nerves axons decreased, leading to mitochondrial disintegration in cells. The mitochondrial activity of Neur-67Q worms was changed, resulting in higher oxygen consumption and lower ATP levels Since neurons, which constituted 302 of the worm's 959 cells, were the only places. Polly was expressed, the alterations were obvious. The severity of the discrepancies suggested that changes in the mitochondrial function of neurons affected other organs as well. Pdr-1 and PRKN deficiency was found in a worm model of Parkinson's disease, with comparable results. Near-67Q worms with drop-1 deletion showed enhanced motility despite reduced ATP levels. Similar results were obtained in wild-type worms with drop-1 deletion, which lowered ATP levels but not motility. 

Disrupting Mitochondrial Fission's Tissue-Specific Effects

In neuronal and muscular polyQ toxicity models, the effects of eliminating drop-1 were studied differently. Different tissues had different levels of mitochondrial fission and fusion. To make things even more interesting, drop-1 deletion in body wall muscle did not affect mitochondrial morphology, whereas reducing drop-1 levels in neurons did.

Conclusion

In HD models in C. elegans, polyglutamine aggregation is linked to mitochondrial breakage and disorganization. Our findings suggest that DRP1 may not be an effective therapeutic target for HD or that great caution must be taken to ensure that just a certain proportion of DRP1 levels are reduced (Traa et al., 2021). In a C. elegans model of HD, we found three new genetic targets in addition to DRP1 that enhanced both crawling and swimming. Mitochondrial fragmentation may be avoided without interfering with the mitochondrial fission mechanism, as shown by these genetic targets. Mitochondria-fragmentation correction techniques may be effective in the treatment of HD.

We conclude by discovering that a C. elegans polyQ neural model had mitochondrial alteration of mobility and shortening of life expectancy. In Neur-67Q worms, reducing the amount of the mitochondrial fission gene drop-1 boosted motility and longevity. (Traa et al., 2021). RNAi clones that minimize mitochondrial fragmentation increased the mobility and survival of Near-67Q worms. HD, other polyQ disorders may be treated by reducing mitochondrial fragmentation while avoiding the harmful effects of changing DRP-1. A lack of evidence concluded that these results would need to be further investigated using the techniques outlined. Nevertheless, the author believes that the method may be utilised to develop computational tools that can infer the size and kind of signalling abnormalities in different illnesses and abnormalities in various diseases. Similar experimental approaches might test the hypotheses on lateral and longitudinal fission/fusion disruption in diverse conditions. Individual mitochondria may be seen exchanging matrix contents as they fuse or separate in real-time.

References

Traa, A., Machiela, E., Rudich, P. D., Soo, S. K., Senchuk, M. M., & Van Raamsdonk, J. M. (2021). Identification of Novel Therapeutic Targets for Polyglutamine Diseases That Target Mitochondrial Fragmentation. International Journal of Molecular Sciences, 22(24), 13447.

Machiela, E., Rudich, P. D., Traa, A., Anglas, U., Soo, S. K., Senchuk, M. M., & Van Raamsdonk, J. M. (2021). Targeting mitochondrial network disorganisation is protective in C. elegans models of Huntington’s disease. Ageing and Disease, 12(7), 1753.

Shah, S. I., Paine, J. G., Perez, C., & Ullah, G. (2019). Mitochondrial fragmentation and network architecture in degenerative diseases. PloS one, 14(9), e0223014.