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Shear Stress, Mechanosensors, and Atherosclerosis
Published in Juhyun Lee, Sharon Gerecht, Hanjoong Jo, Tzung Hsiai, Modern Mechanobiology, 2021
Primary cilia are 3–5 µm long sensory microtubule-like microstructures that protrude into the vessel lumen and respond to biochemical, biophysical, and biomechanical stimuli [33]. Primary cilia have long been considered as a mechanosensing structure that serve as mechanosensors [60] that are critical for calcium influx and the production of NO [61]. Primary cilia were also regarded as a magnifier of mechanosignal [33, 62]. It has been shown that nonciliated cells or cells undergoing chemical removal of cilia show a decrease in shear-responsive transcriptional factor KLF2 [63]. Recent studies have shown that the presence of primary cilia protects against the development of atherosclerotic lesions, evidenced by the deletion of the ciliogenesis gene Lft88, promotes vascular inflammation, and inhibits the activity of eNOS [64]). ECs lacking primary cilia are more susceptible to calcification [65]. Primary cilia are distributed in mouse aorta in an non-uniform manner, with preferential distribution in regions of disturbed flow (predilection sites) [62] but less in atheroprotective regions (where the flow pattern is laminar flow) of mouse aorta. On the basis of the atheroprotective profile of primary cilia, it would be interesting to develop new drugs that can increase the cilia number or activity.
General Introductory Topics
Published in Vadim Backman, Adam Wax, Hao F. Zhang, A Laboratory Manual in Biophotonics, 2018
Vadim Backman, Adam Wax, Hao F. Zhang
Microtubules are formed by the polymers of alpha and beta tubulin. Microtubules originate (“radiate”) from the microtubule originating center (MTOC), which lies near the nucleus in association with centrioles. The role of microtubules as structural elements is to resist compression. One can think of them as support beams. Microtubules are also found in cell flagella (thus enabling cell motility) and cilia. Cilia are structures protruding from the cell surface that are used to move extracellular material, such as mucus. This function, for example, is important in the respiratory epithelium and helps get rid of foreign microorganisms or inorganic microscopic objects that are trapped in the respiratory mucus in a process called mucociliary escalator. Microtubules also assist in mitosis. Their other function is intracellular transport. Associated with motor proteins dynein and kinesin, microtubules help transport organelles like mitochondria or vesicles across a cell. In this process, dynein and kinesin attach and move toward and from, respectively, a cell center. Furthermore, in cell division (mitosis), microtubules are part of the mitotic spindle, the structure that separates the chromosomes into daughter cells.
Classical Biodynamics and Biomechanics
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Cilia and flagella, made from bundles of microtubules and molecular motors that travel on them, provide the motile force for some bacteria as well as for eukaryotic cells. Cilia occur in single-celled eukaryotic ciliates, a group of protists characterized by the presence of hairlike cilia, similar in structure to flagella but typically shorter and present in much larger numbers. The difference between cilia and flagella is usually understood to be the sort of motion: cilia wave back and forth while flagella rotate. Cilia are also sometimes considered to be shorter than flagella. Many of these short cilia undulate in synchronism to generate forces used in swimming, crawling, attachment, and feeding. Upon stimulation by an external force, cilia may also transmit signals to the interior of the ciliate. In larger organisms such as humans, cilia are generally attached to cells that are fixed in place, and have the job of moving fluid and particles by the cells. Prokaryotic bacteria, including Escherichia coli also employ cilia and flagella for movement, though usually in smaller numbers. The multiple flagella of E. coli and other bacteria sometimes form bundles that intertwine and rotate together. As they drive the bacterium forward, they also may induce rotation. Some examples of these cilia and flagella are shown in Figure 12.13. Many others can easily be found by a Web search, including the famous example of paramecium’s large number of cilia. The terms cilia and flagella are occasionally used interchangeably (en.wikipedia.org/wiki/Flagella), so it is important to know the features of the cilium/flagellum of interest.
Entropy generation phenomenon for ciliated pumping flow of aluminum oxide and silver nanoparticles with Hall device significances
Published in Waves in Random and Complex Media, 2023
Khurram Javid, Momen Khan, Sami Ullah Khan
Due to applications of cilia pumping in biological processes, cilia have been stated as a dominant field of research activities to control the transport mechanisms not only in the medical domain but also in the chemical industry. Cilia are tiny hair assemblies, which swells from cell surfaces and play vital roles in motility and development in the bulk of eukaryotes including human. Their capabilities produce a wave structure that generates a periodic motion of surrounding liquids and flagella [1]. These artificially generated waves are known as metachronal waves. In the human body, cilia are present in the brain, lungs, efferent ducts, eyes, and fallopian tubes. The motility of ciliated cells has a remarkable role in the clearance of mucosa in the airways, oocytes motion in the fallopian tubes, and cerebrospinal fluid circulation in the brain. While non-motile cilia exist in human sensory organs such as the nose and eye [2,3]. Some early studies in this domain were comprehensively reviewed by a few researchers and their detail is given in the following references [4–7].
Biomechanics of cilia-assisted flow with hybrid nanofluid phenomena impulses by convective conditions
Published in Waves in Random and Complex Media, 2022
S. Ijaz, N. Nasir, H. sadaf, R. Mehmood
Cilia and flagella protrude from the cell. They are made up of microtubules and sheltered by adding the plasma membrane. They are motile and intended to move the cell itself or to move substances over or around the cell; however, cilia have numerous probable sensory tasks, particularly in nerve cells, where they are immobile. The differences between cilia and flagella include location, length, and movement. Cilia are aplenty on a cell surface, whereas flagella are solitary or rare. Cilia beat together with synchronization, while flagella proceed freely. Cilia are shorter than flagella. Cilia originate only in eukaryotes, whereas flagella originate in prokaryotic and eukaryotic cells.