IU Indianapolis ScholarWorks :: Browsing by Subject "Mechanotransduction"

Browsing by Subject "Mechanotransduction"

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The essential role of Stat3 in bone homeostasis and mechanotransduction
(2014-05) Zhou, Hongkang; Li, Jiliang; Marrs, James; Stocum, David L.; Atkinson, Simon; Aguilar, R. Claudio; Yokota, Hiroki, 1955-
Signal Transducer and Activator of Transcription 3 (Stat3) is a transcription factor expressed in bone and joint cells that include osteoblasts, osteocytes, osteoclasts, and chondrocytes. Stat3 is activated by a variety of cytokines and growth factors, including IL-6/gp130 family cytokines. These cytokines not only regulate the differentiation of osteoblasts and osteoclasts, but also regulate proliferation of chondrocytes through Stat3 activation. In 2007, mutations of Stat3 have been confirmed to cause a rare human immunodeficiency disease – Job syndrome which presents skeletal abnormalities like: reduced bone density (osteopenia), scoliosis, hyperextensibility of joints, and recurrent pathological bone fractures. Changes in the Stat3 gene alter the structure and function of the Stat3 proteins, impairing its ability to control the activity of other genes. However, little is known about the effects of Stat3 mutations on bone cells and tissues. To investigate the in vivo physiological role of Stat3 in bone homeostasis, osteoblast/osteocyte-specific Stat3 knockout (KO) mice were generated via the Cre-LoxP recombination system. The osteoblast/osteocyte-specific Stat3 KO mice showed bone abnormalities and an osteoporotic phenotype because of a reduced bone formation rate. Furthermore, inactivation of Stat3 decreased load-driven bone formation, and the disruption of Stat3 in osteoblasts suppressed load-driven mitochondrial activity, which led to an elevated level of reactive oxygen species (ROS) in cultured primary osteoblasts. Stat3 has been found to be responsive to mechanical stimulation, and might play an important role in mechanical signal transduction in osteocytes. To investigate the role Stat3 plays in mechanical signaling transduction, osteocyte-specific Stat3 knockout (KO) mice were created. Inactivation of Stat3 in osteocytes presented a significantly reduced load-driven bone formation. Decreased osteoblast activity indicated by reduced osteoid surface was also found in osteocyte-specific Stat3 KO mice. Moreover, sclerostin (SOST) protein which is a critical osteocyte-specific inhibitor of bone formation, its encoded gene SOST expression has been found to be enhanced in osteocyte-specific Stat3 KO mice. Thus, these results clearly demonstrated that Stat3 plays an important role in bone homeostasis and mechanotransduction, and Stat3 is not only involved in bone-formation-important genes regulation in the nucleus but also in mediation of ROS and oxidative stress in mitochondria.
GPR68 Senses Flow and Is Essential for Vascular Physiology
(Elsevier, 2018-04-19) Xu, Jie; Mathur, Jayanti; Vessières, Emilie; Hammack, Scott; Nonomura, Keiko; Favre, Julie; Grimaud, Linda; Petrus, Matt; Francisco, Allain; Li, Jingyuan; Lee, Van; Xiang, Fu-Li; Mainquist, James K.; Cahalan, Stuart M.; Orth, Anthony P.; Walker, John R.; Ma, Shang; Lukacs, Viktor; Bordone, Laura; Bandell, Michael; Laffitte, Bryan; Xu, Yan; Chien, Shu; Henrion, Daniel; Patapoutian, Ardem; Obstetrics and Gynecology, School of Medicine
Mechanotransduction plays a crucial role in vascular biology. One example of this is the local regulation of vascular resistance via flow-mediated dilation (FMD). Impairment of this process is a hallmark of endothelial dysfunction and a precursor to a wide array of vascular diseases, such as hypertension and atherosclerosis. Yet the molecules responsible for sensing flow (shear stress) within endothelial cells remain largely unknown. We designed a 384-well screening system that applies shear stress on cultured cells. We identified a mechanosensitive cell line that exhibits shear stress-activated calcium transients, screened a focused RNAi library, and identified GPR68 as necessary and sufficient for shear stress responses. GPR68 is expressed in endothelial cells of small-diameter (resistance) arteries. Importantly, Gpr68-deficient mice display markedly impaired acute FMD and chronic flow-mediated outward remodeling in mesenteric arterioles. Therefore, GPR68 is an essential flow sensor in arteriolar endothelium and is a critical signaling component in cardiovascular pathophysiology.
Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation
(Wiley, 2023) Wang, Ting; Soundararajan, Avinash; Rabinowitz, Jeffrey; Jaiswal, Anant; Osborne, Timothy; Pattabiraman, Padmanabhan Paranji; Ophthalmology, School of Medicine
Trabecular meshwork (TM) cells are contractile and mechanosensitive, and they aid in maintaining intraocular pressure (IOP) homeostasis. Lipids are attributed to modulating TM contractility, with poor mechanistic understanding. In this study using human TM cells, we identify the mechanosensing role of the transcription factors sterol regulatory element binding proteins (SREBPs) involved in lipogenesis. By constitutively activating SREBPs and pharmacologically inactivating SREBPs, we have mechanistically deciphered the attributes of SREBPs in regulating the contractile properties of TM. The pharmacological inhibition of SREBPs by fatostatin and molecular inactivation of SREBPs ex vivo and in vivo, respectively, results in significant IOP lowering. As a proof of concept, fatostatin significantly decreased the SREBPs responsive genes and enzymes involved in lipogenic pathways as well as the levels of the phospholipid, cholesterol, and triglyceride. Further, we show that fatostatin mitigated actin polymerization machinery and stabilization, and decreased ECM synthesis and secretion. We thus postulate that lowering lipogenesis in the TM outflow pathway can hold the key to lowering IOP by modifying the TM biomechanics.
Influence of Peri-duodenal Non-constrictive Cuff on the Body Weight of Rats
(Springer US, 2015-02) Lu, Xiao; Mattar, Samer G.; Kassab, Ghassan S.; Department of Biomedical Engineering, School of Engineering and Technology
Background Weight loss has been found to improve or re- solve cardiovascular comorbidities. There is a significant need for reversible device approaches to weight loss. Methods Non-constrictive cuff (NCC) is made of implantable silicone rubber with an internal diameter greater than the duodenum. Ten or 11 NCC were individually mounted along the duodenum from the pyloric sphincter toward the distal duodenum to cover ~22 mm in the length. Twelve Wistar rats were implanted with NCC, and six served as sham, and both groups were observed over 4 months. Six rats with implant had their NCC removed and were observed for additional 4weeks. Results The food intake decreased from 40.1 to 28.1 g/day after 4 months of NCC implant. The body weight gain decreased from 1.76 to 0.46 g/day after 4 months of NCC implant. The fasting glucose decreased from 87.7 to 75.3 mg/ dl at terminal day. The duodenal muscle layer covered by the NCC increased from 0.133 to 0.334 mm. After 4 weeks of NCC removal, the food intake, body weight gain, and fasting glucose recovered to 36.2, 2.51 g/day, and 83.9 mg/dl. The duodenal muscle layer covered by the NCC decreased to 0.217 mm. Conclusion The NCC implant placed on the proximal duode- num is safe in rats for a 4-month period. The efficacy of the NCC implant is significant for decrease in food intake, body weight gain, and fasting glucose in a normal rat model. The removal of NCC implant confirmed a cause-effect relation with food intake and hence body weight.
The Interaction of Biological Factors with Mechanical Signals in Bone Adaptation: Recent Developments
(Current Science Inc., 2012-06) Robling, Alexander G.; Department of Anatomy & Cell Biology, IU School of Medicine
Mechanotransduction in bone is fundamental to proper skeletal development. Deficiencies in signaling mechanisms that transduce physical forces to effector cells can have severe consequences for skeletal integrity. Therefore, a solid understanding of the cellular and molecular components of mechanotransduction is crucial for correcting skeletal modeling and remodeling errors and designing effective therapies. In recent years, progress has been made on many fronts regarding our understanding of bone cell mechanotransduction, including subcellular localization of mechanosensitive components in bone cells, the discovery of mechanosensitive G-protein- coupled receptors, identification of new ion channels and larger pores (eg, hemichannels) involved in physical signal transduction, and cell adhesion proteins, among others. These and other recent mechanisms are reviewed to provide a synthesis of recent experimental findings, in the larger context of whole bone adaptation.
JAK-STAT and bone metabolism
(Taylor & Francis, 2013) Li, Jiliang; Biology, School of Science
Emerging evidences suggest Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway plays an important role in bone development and metabolism. Effects of JAK-STAT pathway on skeletal development are summarized based on skeletal phenotype of individual JAK and STAT gene knockout mouse. Furthermore, STAT3 has more profound effects on bone homeostasis compared with the other STATs. STAT3 mutation causes a disease called Job syndrome, most patients with which have associated craniofacial and skeletal features. Selective inactivation of STAT3 in osteoblasts decreases bone formation and skeletal responsiveness to mechanical loading. Future research includes investigating JAK-STAT signaling in osteoclasts and osteocytes.
Loss of the auxiliary α2δ1 voltage-sensitive calcium channel subunit impairs bone formation and anabolic responses to mechanical loading
(Oxford University Press, 2024-01-10) Kelly, Madison M.; Sharma, Karan; Wright, Christian S.; Yi, Xin; Reyes Fernandez, Perla C.; Gegg, Aaron T.; Gorrell, Taylor A.; Noonan, Megan L.; Baghdady, Ahmed; Sieger, Jacob A.; Dolphin, Annette C.; Warden, Stuart J.; Deosthale, Padmini; Plotkin, Lilian I.; Sankar, Uma; Hum, Julia M.; Robling, Alexander G.; Farach-Carson, Mary C.; Thompson, William R.; Physical Therapy, School of Health and Human Sciences
Voltage-sensitive calcium channels (VSCCs) influence bone structure and function, including anabolic responses to mechanical loading. While the pore-forming (α1) subunit of VSCCs allows Ca2+ influx, auxiliary subunits regulate the biophysical properties of the pore. The α2δ1 subunit influences gating kinetics of the α1 pore and enables mechanically induced signaling in osteocytes; however, the skeletal function of α2δ1 in vivo remains unknown. In this work, we examined the skeletal consequences of deleting Cacna2d1, the gene encoding α2δ1. Dual-energy X-ray absorptiometry and microcomputed tomography imaging demonstrated that deletion of α2δ1 diminished bone mineral content and density in both male and female C57BL/6 mice. Structural differences manifested in both trabecular and cortical bone for males, while the absence of α2δ1 affected only cortical bone in female mice. Deletion of α2δ1 impaired skeletal mechanical properties in both sexes, as measured by three-point bending to failure. While no changes in osteoblast number or activity were found for either sex, male mice displayed a significant increase in osteoclast number, accompanied by increased eroded bone surface and upregulation of genes that regulate osteoclast differentiation. Deletion of α2δ1 also rendered the skeleton insensitive to exogenous mechanical loading in males. While previous work demonstrates that VSCCs are essential for anabolic responses to mechanical loading, the mechanism by which these channels sense and respond to force remained unclear. Our data demonstrate that the α2δ1 auxiliary VSCC subunit functions to maintain baseline bone mass and strength through regulation of osteoclast activity and also provides skeletal mechanotransduction in male mice. These data reveal a molecular player in our understanding of the mechanisms by which VSCCs influence skeletal adaptation.
The Mechanotransduction of Hydrostatic Pressure by Mesenchymal Stem Cells
(2018-12) Hosseini, Seyedeh Ghazaleh; Wagner, Diane R.; Na, Sungsoo; Ji, Julie
Mesenchymal stem cells (MSCs) are responsive to mechanical stimuli that play an essential role in directing their diﬀerentiation to the chondrogenic lineage. A better understanding of the mechanisms that allow MSCs to respond to mechanical stimuli is important to improving cartilage tissue engineering and regenerative medicine. Hydrostatic pressure (HP) in particular is known to be a primary mechanical force in joints. However, little is known about the underlying mechanisms that facilitate HP mechanotransduction. Understanding the signaling pathways in MSCs in transducing HP to a beneﬁcial biologic response and their interrelationship were the focus of this thesis. Studies used porcine marrow-derived MSCs seeded in agarose gel. Calcium ion Ca++ signaling, focal adhesion kinase (FAK) involvement, and sirtuin1 activity were investigated in conjunction with HP application. Intracellular Ca++ concentration was previously shown to be changed with HP application. In our study a bioreactor was used to apply a single application of HP to the MSC-seeded gel structures and observe Ca++ signaling via live imaging of a ﬂuorescent calcium indicator in cells. However, no ﬂuctuations in Ca++ concentrations were observed with 10 minutes loading of HP. Additionally a problem with the biore actor design was discovered. First the gel was ﬂoating around in the bioreactor even without loading. After stabilizing the gel and stopping it from ﬂoating, there were still about 16 µm of movement and deformation in the system. The movement and deformation was analyzed for the gel structure and diﬀerent parts of the bioreactor. Furthermore, we investigated the role of FAK in early and late chondrogenesis and also its involvement in HP mechanotransduction. A FAK inhibitor was used on MSCs from day 1 to 21 and showed a dose-dependent suppression of chondrogenesis. However, when low doses of FAK inhibitor added to the MSC culture from day 21 to 42, chondrogenesis was not inhibited. With 4 hour cyclic HP, FAK phosphorylation increased. The beneﬁcial eﬀect of HP was suppressed with overnight addition of the FAK inhibitor to MSC medium, suggesting FAK involvement in HP mechanotransd ucation by MSCs. Moreover, sirtuin1 participation in MSC chondrogenesis and mechanotransduc tion was also explored. The results indicated that overnight sirtuin1 inhibition in creased chondrogenic gene expression (Agc, Col2, and Sox9) in MSCs. Additionally, the activity of sirtuin1 was decreased with both 4 hour cyclic hydrostatic pressure and inhibitor application. These two together demonstrated that sirtuin1 inhibition enhances chondrogenesis. In this research we have investigated the role of Ca++ signaling, FAK involvement, and sirtuin1 activity in the mechanotransduction of HP in MSCs. These understand ings about the mechanisms regulating the chondrogenesis with respect to HP could have important implications for cartilage tissue engineering and regenerative studies.
Mechanotransduction of subcellular AMPK and its role in breast cancer cell migration
(2018-04) Steele, Hannah E.; Na, Sungsoo
The biophysical microenvironment of the tumor site has significant impact on breast cancer progression and metastasis. The importance of altered mechanotransduction in cancerous tissue through the integrin-mediated signaling axis has been documented, yet its role in the regulation of cellular metabolism and the potential link between cellular energy and cell migration remain poorly understood. In this study, we investigated the role of mechanotransduction (via Src and FAK) in AMP-activated protein kinase (AMPK) activation in breast cancer cells in response to interstitial fluid flow. Additionally, we explored the involvement of AMPK in breast cancer cell migration. An in-vitro three-dimensional (3D) cell culture model utilizing collagen-Matrigel matrices was used. Interstitial fluid flow was applied to the 3D cell-matrix construct inside a flow chamber. The sub-cellular signaling activity of Src, FAK, and AMPK was visualized in real-time using fluorescent resonance energy transfer (FRET). We observed that breast cancer cells (MDA-MB-231) are more sensitive to interstitial fluid flow than normal epithelial cells (MCF-10A) in the regulation of FAK and Src. AMPK was activated in the mitochondria of MDA-MB-231 cells by interstitial fluid flow, but not in other subcellular domains (i.e., cytosol, plasma membrane, and nucleus). Subcellular AMPK in MCF-10A cells did not respond to interstitial fluid flow. The inhibition of FAK or Src abolished flow-induced AMPK activation in the mitochondria of MDA-MB-231 cells. We also observed that global AMPK activation reduced MDA-MB-231 cell migration. Interestingly, specific AMPK inhibition in the mitochondria reduced cell migration and blocked interstitial fluid flow-induced cell migration. Our results suggest the linkage of FAK/Src and mitochondria-specific AMPK in mechanotransduction and the dual role of AMPK in breast cancer cell migration depending on its subcellular activation. Therefore, subcellular AMPK activation may play an important and distinct role in cancer invasion and progression.
The murine catecholamine methyltransferase mTOMT is essential for mechanotransduction by cochlear hair cells
(eLife Sciences Publications, 2017-05-15) Cunningham, Christopher L.; Wu, Zizhen; Jafari, Aria; Zhao, Bo; Schrode, Kat; Harkins-Perry, Sarah; Lauer, Amanda; Müller, Ulrich; Otolaryngology -- Head and Neck Surgery, School of Medicine
Hair cells of the cochlea are mechanosensors for the perception of sound. Mutations in the LRTOMT gene, which encodes a protein with homology to the catecholamine methyltransferase COMT that is linked to schizophrenia, cause deafness. Here, we show that Tomt/Comt2, the murine ortholog of LRTOMT, has an unexpected function in the regulation of mechanotransduction by hair cells. The role of mTOMT in hair cells is independent of mTOMT methyltransferase function and mCOMT cannot substitute for mTOMT function. Instead, mTOMT binds to putative components of the mechanotransduction channel in hair cells and is essential for the transport of some of these components into the mechanically sensitive stereocilia of hair cells. Our studies thus suggest functional diversification between mCOMT and mTOMT, where mTOMT is critical for the assembly of the mechanotransduction machinery of hair cells. Defects in this process are likely mechanistically linked to deafness caused by mutations in LRTOMT/Tomt.

Browsing by Subject "Mechanotransduction"

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