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Pathogenesis: Molecular mechanisms of osteoporosis
Published in Peter V. Giannoudis, Thomas A. Einhorn, Surgical and Medical Treatment of Osteoporosis, 2020
Anastasia E. Markatseli, Theodora E. Markatseli, Alexandros A. Drosos
Osteoclasts are primarily responsible for bone resorption. Osteoclasts are multinucleated giant cells derived from precursor cells of the monocyte-macrophage lineage (39,40). Mononuclear cells are attracted to the point of the bone surface that will be absorbed and proliferate and differentiate into preosteoclasts. The fusion of mononuclear preosteoclasts follows, which results in the creation of the multinucleated osteoclast. First, the mature osteoclast is firmly adhered to the bone with the help of specialized podosomes, which are rich in actin. Among the highly corrugated surface of the osteoclast and the bone surface, a closed cavity is formed. The osteoclast secretes proteolytic enzymes (cathepsin K) and hydrochloric acid (hydrogen ions) into the cavity (41). Proteolytic enzymes contribute to the fragmentation of the organic phase, while the hydrogen ions dissolve the inorganic phase. It should be noted that the carbonic anhydrase II is an enzyme found in the cytoplasm of the osteoclast and contributes to the production of hydrogen ions. Therefore, the main function of osteoclasts is the absorption of the matrix, which is achieved through the creation of absorption cavities (Howship lacunae) (40). The process of bone resorption is completed with the apoptosis of osteoclast. Throughout the absorption, osteoclasts release substances, and bone tissue also releases local factors that ultimately inhibit the action of osteoclasts and induce osteoblast activity (signals are transmitted to osteoblasts in order to present in the absorption cavities) (42).
Cytoskeletons (F-actin) and spermatogenesis
Published in C. Yan Cheng, Spermatogenesis, 2018
Liza O’Donnell, Peter G. Stanton
The tubulobulbar complex (TBC) is a novel structure comprised of a tubular extension of plasma membranes surrounded by a cuff of cross-linked actin (Figure 15.2) to which various actin-binding proteins are localized. At the end of this F-actin-associated tubular extension is a so-called bulbous structure, surrounded by endoplasmic reticulum but not actin, which extends into a clathrin-coated pit. Many studies have shown that TBCs are a novel endocytic structure similar to podosomes, and their major function is the removal and recycling of intercellular junctions.69 TBCs are readily found at apical junctions between Sertoli cells and advanced spermatids and are well described at this site.69 These structures form on the ventral side of the spermatid nucleus at the beginning of spermiation (stage VII in rodents) and they persist throughout spermiation, where they are involved in the removal of ES and other junction-associated proteins as well as remodeling the spermatid plasma membrane prior to its release into the lumen.69
Structure, Biochemical Properties, and Biological Functions of Integrin Cytoplasmic Domains
Published in Yoshikazu Takada, Integrins: The Biological Problems, 2017
Martin E. Hemler, Jonathan B. Weitzman, Renata Pasqualini, Satoshi Kawaguchi, Paul D. Kassner, Feodor B. Berdichevsky
Integrins may not only localize to focal adhesions, but also to other types of subcellular structures such as podosomes158,159 or point contacts.80 At present, there is no information regarding specific roles for cytoplasmic domains for localization to these other structures.
Polygenic risk for traumatic loss-related PTSD in US military veterans: Protective effect of secure attachment style
Published in The World Journal of Biological Psychiatry, 2021
Ruth H. Asch, Irina Esterlis, Frank R. Wendt, Lorig Kachadourian, Steven M. Southwick, Joel Gelernter, Renato Polimanti, Robert H. Pietrzak
In our exploratory PTSDREX PRS gene set enrichment analysis, the strongest result was observed for genes involved in podosome cellular structure. Genes involved in invadopodium structure and function (GO: 0071437) also emerged. Podosomes and invadopodia are microglial structures that mediate inflammatory responses and matrix remodelling following disease or injury (Vincent et al. 2012). Podosomes and invadopodia are further implicated neuron motility and neurite outgrowth, thereby influencing neurodevelopment and plasticity (Tanna et al. 2019). Although no known studies have investigated the role of these cellular structures in PTSD pathogenesis, a recent multivariate gene-by-environment genome–wide interaction study in >120,000 UK Biobank participants identified extracellular matrix biology and synaptic plasticity as biological mediators of the effects of PTSD and trauma on genetic risk for suicidal behaviour (Wendt et al. 2020). Taken together, these findings suggest a need for further study into the possible role of extracellular matrix and glial structural elements in the pathophysiology of PTSD (Bach et al. 2019).
Megakaryocyte emperipolesis: a new frontier in cell-in-cell interaction
Published in Platelets, 2020
Pierre Cunin, Peter A. Nigrovic
Microscopic observation shows that emperipolesis is a dynamic process wherein both cells participate actively [21]. Neutrophils polarize toward the point of entry and demonstrate directed migration toward the MK, sometimes protruding podosomes into the MK before entry. The MK itself forms an actin-lined cup at the site of neutrophil engagement, similar to the transmigratory cup observed during transcellular migration [33,34]. Prominent actin polymerization is observed within the MK, layered under the surface membrane at the point of contact with the neutrophil and surrounding the emperisome containing an internalized neutrophil (Figure 2 and [21]). Surprisingly, the tubulin cytoskeleton seems to have no essential role, since tubulin polymerization is not observed around the internalized neutrophil and the tubulin inhibitor nocodazole does not inhibit emperipolesis [21].
Live imaging of single platelets at work
Published in Platelets, 2020
Karin Sadoul, Laurence Lafanechère, Alexei Grichine
The use of platelets isolated from GFP-actin (green-fluorescent protein fused to actin) expressing mice has revealed a new type of actin organization, called actin nodules, which form before actin stress fibers appear in spread platelets [2]. The dynamics of actin nodules during platelet spreading on a fibrinogen-coated surface has been nicely quantified by combining Total Internal Reflection Fluorescence (TIRF) and epifluorescence microscopy using platelets purified from mice expressing Lifeact (a 17 aa actin-binding peptide) fused to GFP [3]. Nodules increase in number during the first 20 sec of spreading and have a lifetime of about 22 sec. Their size is ~0.22 μm2 (at appearance and disappearance) but increases to ~0.31 μm2 at midlife due to both, actin polymerization and a downwards movement of 34.6 nm toward the substrate. These features are similar to podosome dynamics in megakaryocytes [4], albeit much faster and without substrate degradation. The podosome-like protein organization of fixed actin nodules was then described in more detail by higher resolution microscopy (dSTORM, SIM and EM, see also the review about super-resolution microscopy by Khan and Pike in the same issue).