Mechanical properties of crosslinks controls failure mechanism of hierarchical intermediate filament networks

Intermediate filaments are one of the key components of the cytoskeleton in eukaryotic cells, and their mechanical properties are found to be equally important for physiological function and disease. While the mechanical properties of single full length filaments have been studied, how the mechanical properties of crosslinks affect the mechanical property of the intermediate filament network is not well understood. This paper applies a mesoscopic model of the intermediate network with varied crosslink strengths to investigate its failure mechanism under the extreme mechanical loading. It finds that relatively weaker crosslinks lead to a more flaw tolerant intermediate filament network that is also 23% stronger than the one with strong crosslinks. These findings suggest that the mechanical properties of interfacial components are critical for bioinspired designs which provide intriguing mechanical properties.

Computational and theoretical modeling of intermediate filament networks:Structure,mechanics and disease

Intermediate filaments, in addition to microtubules and actin microfilaments, are one of the three major components of the cytoskeleton in eukaryotic cells. It was discovered during the recent decades that in most cells, intermediate filament proteins play key roles to reinforce cells subjected to large-deformation, and that they participate in signal transduction, and it was proposed that their nanome- chanical properties are critical to perform those functions. However, it is still poorly understood how the nanoscopic structure, as well as the combination of chemical composition, molecular structure and interfacial properties of these protein molecules contribute to the biomechanical properties of filaments and filament networks. Here we review recent progress in computational and theoretical studies of the intermediate filaments network at various levels in the protein＇s structure. A multiple scale method is discussed, used to couple molecular modeling with atomistic detail to larger-scale material properties of the networked material. It is shown that a finer-trains-coarser method- ology as discussed here provides a useful tool in understanding the biomechanical property and disease mechanism of intermediate filaments, coupling experiment and simulation. It further allows us to improve the understanding of associated disease mechanisms and lays the foundation for engineering the mechanical properties of biomaterials.

Nestin in gastrointestinal and other cancers: Effects on cells and tumor angiogenesis

Nestin is a class Ⅵ intermediate filament protein that was originally described as a neuronal stem cell marker during central nervous system (CNS) development, and is currently widely used in that capacity. Nestin is also expressed in non-neuronal immature or progenitor cells in normal tissues. Under pathological conditions, nestin is expressed in repair processes in the CNS, muscle, liver, and infarcted myocardium. Furthermore, increased nestin expression has been reported in various tumor cells, including CNS tumors, gastrointestinal stromal tumors, pancreatic cancer, prostate cancer, breast cancer, malignant melanoma, dermatofibrosarcoma protuberances, and thyroid tumors. Nestin is reported to correlate with aggressive growth, metastasis, and poor prognosis in some tumors; however, the roles of nestin in cancer cells have not been well characterized. Furthermore, nestin is more specifically expressed in proliferating small-sized tumor vessels in glioblastoma and gastric, colorectal, and prostate cancers than are other tumor vessel markers. These findings indicate that nestin may be a marker for newly synthesized tumor vessels and a therapeutic target for tumor angiogenesis. It has received a lot of attention recently as a cancer stem cell marker in various cancer cells including brain tumors, malignant rhabdoid tumors, and uterine, cervical, prostate, bladder, head and neck, ovarian, testicular, and pancreatic cancers. The purpose of this review is to clarify the roles of nestin in cancer cells and in tumor angiogenesis, and to examine the association between nestin and cancer stem cells. Nestin has the potential to serve as a molecular target for cancers with nestin-positive cancer cells and nestin-positive tumor vasculature.

Maternal zinc deficiency impairs brain nestin expression in prenatal and postnatal mice

Effects of maternal dietary zinc deficiency on prenatal and postnatal brain development were investigated in ICR strain mice. From d 1 of pregnancy (E0) until postnatal d 20 (P20), maternal mice were fed experimental diets that contained 1 mg Zn/kg/day (severe zinc deficient, SZD), 5 mg Zn/kg/day (marginal zinc deficient, MZD), 30 mg Zn/kg/day (zinc adequately supplied, ZA) or 100 mg Zn/kg/day (zinc supplemented, ZS and pair-fed, PF). Brains of offspring from these dietary groups were examined at various developmental stages for expression of nestin, an intermediate filament protein found in neural stem cells and young neurons. Immunocytochemistry showed nestin expression in neural tube 10.5 d post citrus (dpc) as well as in the cerebral cortex and neural tube from 10.5 dpc to postnatal d 10 (P10). Nestin immunoreactivities in both brain and neural tube of those zinc-supplemented control groups (ZA, ZS, PF) were stronger than those in zinc-deficient groups (SZD and MZD). Western blot analysis confirmed that nestin levels in pooled brain extracts from each of the zinc-supplemented groups (ZA, ZS, PF) were much higher than those from the zinc-deficient groups (SZD and MZD) from 10.5 dpc to P10. Immunostaining and Western blots showed no detectable nestin in any of the experimental and control group brains after P20. These observations of an association between maternal zinc deficiency and decreased nestin protein levels in brains of offspring suggest that zinc deficiency suppresses development of neural stem cells, an effect which may lead to neuroanatomical and behavioral abnormalities in adults.

Bone morphogenetic protein-7 induced bone marrow stromal cells differentiate into neuron-like cells

Bone morphogenetic protein-7 is widely accepted as an inducer for bone marrow stem cells differentiating into osteoblasts and chondrocytes. Whether bone marrow stromal cells differentiate into neuron-like cells remains unclear. The current study examined the presence of positive cells for intermediate filament protein and microtubule associated protein-2 in the cytoplasm of bone marrow stromal cells induced by bone morphogenetic protein-7 under an inverted microscope, while no expression of glial fibrillary acidic protein was found. Reverse transcription PCR electrophoresis also revealed a positive target band for intermediate filament protein and microtubule-associated protein 2 mRNA. These results confirmed that bone morphogenetic protein-7 induces rat bone marrow stromal cells differentiating into neuron-like cells.

Intermediate filament dynamics： Disassembly regulation

A mechanism of intermediate filament disassembly regulation is proposed in which disas- sembly is regulated by the amount of proteins assembled in networks. It is Mso hypothe- sized that a delay might exist between regulation and actuM disassembly. Under realistic biological conditions of assembly and disassembly, it is shown that such a delay is harm- less and does not destabilize the organization of intermediate filaments in networks. However, for high rates of disassembly, the model predicts that delay can destabilize the organization, with the intermediate filament material oscillating between organizations mainly in networks and in nonfilamentous particles.

Time course of expression of intermediate filament protein vimentin,nestin and desmin in rat renal glomerular injury

Podocytes in renal glomemlus express unusual intermediate filament proteins （IFs） for visceral epithelial cells. IFs cytoskeleton is mainly composed of vimentin, nestin and desmin. Tissue injury is often accompanied by changes in gene expression of IFs. Enhanced desmin staining in variety of rat experimental including 2 4 puromycin nephrosis. It has not podocytes are observed in a models of podocyte injury aminonucleoside （PAN） been elucidated whether expression of vimentin and nestin is up-regulated in podocyte injury. To further gain insight into expression of IFs in podocytes, we investigated the time course of vimentin, nestin and desmin in PAN nephrosis.

The regulation of host cytoskeleton during SARS-CoV-2 infection in the nervous system

The global economy and public health are currently under enormous pressure since the outbreak of COVID-19. Apart from respiratory discomfort, a subpopulation of COVID-19 patients exhibits neurological symptoms such as headache, myalgia, and loss of smell. Some have even shown encephalitis and necrotizing hemorrhagic encephalopathy. The cytoskeleton of nerve cells changes drastically in these pathologies, indicating that the cytoskeleton and its related proteins are closely related to the pathogenesis of nervous system diseases. In this review, we present the up-to-date association between host cytoskeleton and coronavirus infection in the context of the nervous system. We systematically summarize cytoskeleton-related pathogen-host interactions in both the peripheral and central nervous systems, hoping to contribute to the development of clinical treatment in COVID-19 patients.

Cytoskeletal changes in diseases of the nervous system

The neuronal cytoskeleton not only provides the structural backbone of neurons, but also plays a fundamental role in maintaining neuronal functions. Dysregulation of neuronal architecture is evident in both injury and diseases of the central nervous system. These changes often result in the disruption of protein trafficking, loss of synapses and the death of neurons, ultimately impacting on signal transmission and manifesting in the disease phenotype. Furthermore, mutations in cytoskeletal proteins have been implicated in numerous diseases and, in some cases, identified as the cause of the disease, highlighting the critical role of the cytoskeleton in disease pathology. This review focuses on the role of cytoskeletal proteins in the pathology of mental disorders, neurodegenerative diseases and motor function deficits. In particular, we illustrate how cytoskeletal proteins can be directly linked to disease pathology and progression.

Cytoskeleton-a crucial key in host cell for coronavirus infection

The emerging coronavirus(CoV)pandemic is threatening the public health all over the world.Cytoskeleton is an intricate network involved in controlling cell shape,cargo transport,signal transduction,and cell division.Infection biology studies have illuminated essential roles for cytoskeleton in mediating the outcome of host-virus interactions.In this review,we discuss the dynamic interactions between actin filaments,microtubules,intermediate filaments,and CoVs.In one round of viral life cycle,CoVs surf along filopodia on the host membrane to the entry sites,utilize specific intermediate filament protein as co-receptor to enter target cells,hijack microtubules for transportation to replication and assembly sites,and promote actin filaments polymerization to provide forces for egress.During CoV infection,disruption of host cytoskeleton homeostasis and modification state is tightly connected to pathological processes,such as defective cytokinesis,demyelinating,cilia loss,and neuron necrosis.There are increasing mechanistic studies on cytoskeleton upon CoV infection,such as viral protein-cytoskeleton interaction,changes in the expression and post-translation modification,related signaling pathways,and incorporation with other host factors.Collectively,these insights provide new concepts for fundamental virology and the control of CoV infection.

Nestin expression and proliferation of ependymal cells in adult rat spinal cord after injury

OBJECTIVE: To determine cell proliferation and nestin expression in the ependyma of adult rat spinal cord after injury. METHODS: Rat spinal cord injury models were established by aneurysm clip compression, and nestin expression and proliferation of ependymal cells at different times were shown with pathological and immuno-histochemical staining. RESULTS: Ependymal cells adjacent to the injured site demonstrated a dramatic increase in nestin expression 24 hours after compression. Proliferating cell nuclear antigen was positive, and significant proliferation was observed after 7 days. Nestin expression was down regulated as time went by. CONCLUSION: Normally quiescent mature ependymal cells appear to revert to an embryonic state in response to spinal cord injury.

Effect of dl-praeruptorin A on desmin and vimentin content in rat ischemia/reperfusion myocardiocytes

Background Intermediate filament （IF） proteins have been thought to play a role in nuclear centration, organelle movement and maintenance of cell shape, dl-praeruptorin A （Pd-la）, a novel Ca^2＋-influx blocker and K^＋-channel opener isolated from Chinese traditional herbal medicine Qian-Hu, has been demonstrated to inhibit expression of apoptosis related proteins and reduce the level of proinflammatory factors in ischemia/reperfusion myocardiocytes. Morphologically, whether Pd-la effects myocardiocyte IFs remains unclear. The purpose of this study was, for the first time, to evaluate the in vivo effects of Pd-la on IF desmin and vimentin content in order to further explore its cardioprotection against ischemia and elucidate its mechanism of action. Methods Rats underwent a 30 minutes coronary occlusion followed by 120 minutes reperfusion. Assessment of desmin and vimentin content of myocardiocytes was performed by immunohistochemistry, Western blot, Hematoxylin-Eosin staining and densitometry. Results Pretreatment with i.v. infusion of Pd-la prior to ischemia significantly increased desmin and vimentin content and alleviated defects caused by the ischemia/reperfusion insult, e.g. with Pd-la at a dose of 0.5 or 1.0 mg/kg, integrated density values of desmin were increased from 61 478 ± 10 074 to 177 408 ±10 395 and 195 784±20 057, and vimentin from 59 189± 19 853 to 164 781± 19 543 and 185 696± 20 957 （P〈0.01, vs placebo）, respectively. The recovery of desmin seemed to be stronger and appeared earlier than that of vimentin. Conclusion Pd-la protectively increased IF desmin and vimentin content in ischemia/reperfusion myocardiocytes, which might be partially responsible for its cardioprotection against ischemia.

Super-sensitive bifunctional nanoprobe: Self-assembly of peptide-driven nanoparticles demonstrating tumor fluorescence imaging and therapy

The development of nanomedicine has recently achieved several breakthroughs in the field of cancer treatment;however,biocompatibility and targeted penetration of these nanomaterials remain as limitations,which lead to serious side effects and significantly narrow the scope of their application.The self-assembly of intermediate filaments with arginine-glycine-aspartate(RGD)peptide(RGDIFP)was triggered by the hydrophobic cationic molecule 7-amino actinomycin D(7-AAD)to synthesize a bifunctional nanoparticle that could serve as a fluorescent imaging probe to visualize tumor treatment.The designed RGD-IFP peptide possessed the ability to encapsulate 7-AAD molecules through the formation of hydrogen bonds and hydrophobic interactions by a one-step method.This fluorescent nanoprobe with RGD peptide could be targeted for delivery into tumor cells and released in acidic environments such as endosomes/lysosomes,ultimately inducing cytotoxicity by arresting tumor cell cycling with inserted DNA.It is noteworthy that the RGD-IFP/7-AAD nanoprobe tail-vein injection approach demonstrated not only high tumor-targeted imaging potential,but also potent antitumor therapeutic effects in vivo.The proposed strategy may be used in peptide-driven bifunctional nanoparticles for precise imaging and cancer therapy.

Discovery of Trametinib as an orchestrator for cytoskeletal vimentin remodeling

The dynamic remodeling of the cytoskeletal network of vimentin intermediate filaments supports various cellular functions,including cell morphology,elasticity,migration,organelle localization,and resistance against mechanical or pathological stress.Currently available chemicals targeting vimentin predominantly induce network reorganization and shrinkage around the nucleus.Effective tools for long-term manipulation of vimentin network dispersion in living cells are still lacking,limiting in-depth studies on vimentin function and potential therapeutic applications.Here,we verified that a commercially available small molecule,trametinib,is capable of inducing spatial spreading of the cellular vimentin network without affecting its transcriptional or Translational regulation.Further evidence confirmed its low cytotoxicity and similar effects on different cell types.Importantly,Trametinib has no impact on the other two cytoskeletal systems,actin filaments and the microtubule network.Moreover,Trametinib regulates vimentin network dispersion rapidly and efficiently,with effects persisting for up to 48 h after drug withdrawal.We also ruled out the possibility that Trametinib directly affects the phosphorylation level of vimentin.In summary,we identified an unprecedented regulator Trametinib,which is capable of spreading the vimentin network toward the cell periphery,and thus complemented the existing repertoire of vimentin remodeling drugs in the field of cytoskeletal research.