Elevation of Intra-Cellular Calcium in Nucleus Pulposus Cells with Micro-Pipette-Guided Ultrasound

Ultrasound-mediated spatial and temporal control of engineered cells in vivo

Remote regulation of cells in deep tissue remains a significant challenge. Low-intensity pulsed ultrasound offers promise for in vivo therapies due to its non-invasive nature and precise control. This study uses pulsed ultrasound to control calcium influx in mammalian cells and engineers a therapeutic cellular device responsive to acoustic stimulation in deep tissue without overexpressing calcium channels or gas vesicles. Pulsed ultrasound parameters are established to induce calcium influx in HEK293 cells. Additionally, cells are engineered to express a designed calcium-responsive transcription factor controlling the expression of a selected therapeutic gene, constituting a therapeutic cellular device. The engineered sonogenetic system's functionality is demonstrated in vivo in mice, where an implanted anti-inflammatory cytokine-producing cellular device effectively alleviates acute colitis, as shown by improved colonic morphology and histopathology. This approach provides a powerful tool for precise, localized control of engineered cells in deep tissue, showcasing its potential for targeted therapeutic delivery.

Sonogenetics for Monitoring and Modulating Biomolecular Function by Ultrasound

Ultrasound technology, synergistically harnessed with genetic engineering and chemistry concepts, has started to open the gateway to the remarkable realm of sonogenetics-a pioneering paradigm for remotely orchestrating cellular functions at the molecular level. This fusion not only enables precisely targeted imaging and therapeutic interventions, but also advances our comprehension of mechanobiology to unparalleled depths. Sonogenetic tools harness mechanical force within small tissue volumes while preserving the integrity of the surrounding physiological environment, reaching depths of up to tens of centimeters with high spatiotemporal precision. These capabilities circumvent the inherent physical limitations of alternative in vivo control methods such as optogenetics and magnetogenetics. In this review, we first discuss mechanosensitive ion channels, the most commonly utilized sonogenetic mediators, in both mammalian and non-mammalian systems. Subsequently, we provide a comprehensive overview of state-of-the-art sonogenetic approaches that leverage thermal or mechanical features of ultrasonic waves. Additionally, we explore strategies centered around the design of mechanochemically reactive macromolecular systems. Furthermore, we delve into the realm of ultrasound imaging of biomolecular function, encompassing the utilization of gas vesicles and acoustic reporter genes. Finally, we shed light on limitations and challenges of sonogenetics and present a perspective on the future of this promising technology.

ASIC3 roles in mechanosensitive elongation of nucleus pulposus cells

Morphological changes of the nucleus pulposus (NP) cells occur concomitantly as part of the intervertebral disc (IVD) degeneration and excessive mechanical loading has been speculated as a significant key factor for contributing to such morphological changes. Therefore, we hypothesize that stress exerted on NP cells can cause a deformity of nucleus in response. The changes of cell morphology is observed in degenerative nucleus pulposus. One of the reasons for degeneration of NP is due to overloading of NP especially in the obese population. So the nucleus deformity caused by stress/force is of our study interest. To delineate the effects and role of mechanical stress, we developed a 3D assay using hydrogel cultures with a circular hole generated with needle indentation to simulate a local stress concentration along the edge of the hole. A stressed zone, encompassing 100 μm of range from the circular edge, is defined based on stress concentration calculation to enable quantitative analysis against the control zone. Our results demonstrated that the circular hole produces stress-induced morphological changes in NP cells. The tangential elongation of NP cells and their nucleus shape changes in the stressed zone are significantly increased compared to the non-stressed control zone. It is proposed that the cell elongation is a direct response to elevated stress within the stressed zone. Subsequently we found the stress induced morphological changes of the NP cells can be significantly reduced by inhibiting ASIC3. This suggests ASIC3 plays an important role of play in mechano-signaling of NP cells.

Genetic exploration of roles of acid-sensing ion channel subtypes in neurosensory mechanotransduction including proprioception

Although acid-sensing ion channels (ASICs) are proton-gated ion channels responsible for sensing tissue acidosis, accumulating evidence has shown that ASICs are also involved in neurosensory mechanotransduction. However, in contrast to Piezo ion channels, evidence of ASICs as mechanically gated ion channels has not been found using conventional mechanoclamp approaches. Instead, ASICs are involved in the tether model of mechanotransduction, with the channels gated via tethering elements of extracellular matrix and intracellular cytoskeletons. Methods using substrate deformation-driven neurite stretch and micropipette-guided ultrasound were developed to reveal the roles of ASIC3 and ASIC1a, respectively. Here we summarize the evidence supporting the roles of ASICs in neurosensory mechanotransduction in knockout mouse models of ASIC subtypes and provide insight to further probe their roles in proprioception.

Achilles' Heel-The Significance of Maintaining Microenvironmental Homeostasis in the Nucleus Pulposus for Intervertebral Discs

The dysregulation of intracellular and extracellular environments as well as the aberrant expression of ion channels on the cell membrane are intricately linked to a diverse array of degenerative disorders, including intervertebral disc degeneration. This condition is a significant contributor to low back pain, which poses a substantial burden on both personal quality of life and societal economics. Changes in the number and function of ion channels can disrupt the water and ion balance both inside and outside cells, thereby impacting the physiological functions of tissues and organs. Therefore, maintaining ion homeostasis and stable expression of ion channels within the cellular microenvironment may prove beneficial in the treatment of disc degeneration. Aquaporin (AQP), calcium ion channels, and acid-sensitive ion channels (ASIC) play crucial roles in regulating water, calcium ions, and hydrogen ions levels. These channels have significant effects on physiological and pathological processes such as cellular aging, inflammatory response, stromal decomposition, endoplasmic reticulum stress, and accumulation of cell metabolites. Additionally, Piezo 1, transient receptor potential vanilloid type 4 (TRPV4), tension response enhancer binding protein (TonEBP), potassium ions, zinc ions, and tungsten all play a role in the process of intervertebral disc degeneration. This review endeavors to elucidate alterations in the microenvironment of the nucleus pulposus during intervertebral disc degeneration (IVDD), with a view to offer novel insights and approaches for exploring therapeutic interventions against disc degeneration.

Activation of Mechanosensitive Ion Channels by Ultrasound

Mechanosensitive channels (MSCs) play an important role in how cells transduce mechanical stimuli into electrical or chemical signals, which provides an interventional possibility through the manipulation of ion channel activation using different mechanical stimulation conditions. With good spatial resolution and depth of penetration, ultrasound is often proposed as the tool of choice for such therapeutic applications. Despite the identification of many ion channels as mechanosensitive in recent years, only a limited number of MSCs have been reported to be activated by ultrasound with substantial evidence. Furthermore, although many therapeutic implications using ultrasound have been explored, few offered insights into the molecular basis and the biological effects induced by ultrasound in relieving pain and accelerate tissue healing. In this review, we examined the literature, in particular studies that provided evidence of cellular responses to ultrasound, with and without the target ion channels. The ultrasound activation conditions were then summarized for these ion channels, and these conditions were related to their mode of activation based on the current biological concepts. The overall goal is to bridge the results relating to the activation of MSCs that is specific for ultrasound with the current knowledge in molecular structure and the available physiological evidence that may have facilitated such phenomena. We discussed how collating the information revealed by available scientific investigations helps in the design of a more effective stimulus device for the proposed translational purposes. Traditionally, studies on the effects of ultrasound have focused largely on its mechanical and physical interaction with the targeted tissue through thermal-based therapies as well as non-thermal mechanisms including ultrasonic cavitation; gas body activation; the direct action of the compressional, tensile and shear stresses; radiation force; and acoustic streaming. However, the current review explores and attempts to establish whether the application of low-intensity ultrasound may be associated with the activation of specific MSCs, which in turn triggers relevant cell signaling as its molecular mechanism in achieving the desired therapeutic effects. Non-invasive brain stimulation has recently become an area of intense research interest for rehabilitation, and the implication of low-intensity ultrasound is particularly critical given the need to minimize heat generation to preserve tissue integrity for such applications.

Dynamic Pressure Stimulation Upregulates Collagen II and Aggrecan in Nucleus Pulposus Cells Through Calcium Signaling

STUDY DESIGN

An in vitro study to investigate the effect of pressure stimulation on nucleus pulposus (NP) cells.

OBJECTIVE

The aim of this study was to investigate the question whether physical stimulation can be leveraged to enhance extracellular matrix (ECM) synthesis as a preventive measure for intervertebral disc (IVD) degeneration.

SUMMARY OF BACKGROUND DATA

ECM plays an important role in regulating hydration and pressure balance of the IVD.

METHODS

Cellular stimulation devices with different pressurizing protocols were used to create a pressurized environment to cells cultures. The setup was used to mimic the pressurized conditions within IVD to investigate the effect of pressure stimulation on NP cells.

RESULTS

Pressure stimulation at 300 kPa can enhance the synthesis of ECM proteins Collagen II and aggrecan in NP cells and the effect of dynamic pressure stimulation outperformed the static one. The difference between static and dynamic pressure stimulation was due primarily to calcium signaling activated by pressure fluctuation. The superior effect of dynamic pressure holds for a wide range of stimulation durations, relating to the range of spontaneous calcium oscillations in NP cells.

CONCLUSION

The results link mechanotransduction to the downstream ECM protein synthesis and suggest slow exercises that correspond with spontaneous calcium oscillations in NP cells can be effective to stimulate ECM synthesis in IVD.

Force From Filaments: The Role of the Cytoskeleton and Extracellular Matrix in the Gating of Mechanosensitive Channels

The senses of proprioception, touch, hearing, and blood pressure on mechanosensitive ion channels that transduce mechanical stimuli with high sensitivity and speed. This conversion process is usually called mechanotransduction. From nematode MEC-4/10 to mammalian PIEZO1/2, mechanosensitive ion channels have evolved into several protein families that use variant gating models to convert different forms of mechanical force into electrical signals. In addition to the model of channel gating by stretching from lipid bilayers, another potent model is the opening of channels by force tethering: a membrane-bound channel is elastically tethered directly or indirectly between the cytoskeleton and the extracellular molecules, and the tethering molecules convey force to change the channel structure into an activation form. In general, the mechanical stimulation forces the extracellular structure to move relative to the cytoskeleton, deforming the most compliant component in the system that serves as a gating spring. Here we review recent studies focusing on the ion channel mechanically activated by a tethering force, the mechanotransduction-involved cytoskeletal protein, and the extracellular matrix. The mechanosensitive channel PIEZO2, DEG/ENaC family proteins such as acid-sensing ion channels, and transient receptor potential family members such as NompC are discussed. State-of-the-art techniques, such as polydimethylsiloxane indentation, the pillar array, and micropipette-guided ultrasound stimulation, which are beneficial tools for exploring the tether model, are also discussed.

Auditory independent low-intensity ultrasound stimulation of mouse brain is associated with neuronal ERK phosphorylation and an increase of Tbr2 marked neuroprogenitors

Transcranial ultrasound stimulation is an emerging technique for the development of a non-invasive neuromodulation device for the treatment of various types of neurodegenerations and brain damages. However, there are very few studies that have quantified the optimal ultrasound dosage and the long-term associated effects of transcranial ultrasound treatments of brain diseases. In this study, we used a simple ex vivo hippocampal tissues stimulated by different dosages of ultrasound in combination with different chemical treatments to quantify the required energy for a measurable effect. After determining the most desirable ex vivo stimulation conditions, it was then replicated for the in vivo mouse brains. It was discovered that transcranial ultrasound promoted the increase of Tbr2-expressing neural progenitors in an ASIC1a-dependent manner. Furthermore, such effect was observable at least a week after the initial ultrasound treatments and was not abolished by auditory toxicity.

ASIC1a is required for neuronal activation via low-intensity ultrasound stimulation in mouse brain

Accumulating evidence has shown transcranial low-intensity ultrasound can be potentially a non-invasive neural modulation tool to treat brain diseases. However, the underlying mechanism remains elusive and the majority of studies on animal models applying rather high-intensity ultrasound that cannot be safely used in humans. Here, we showed low-intensity ultrasound was able to activate neurons in the mouse brain and repeated ultrasound stimulation resulted in adult neurogenesis in specific brain regions. In vitro calcium imaging studies showed that a specific ultrasound stimulation mode, which combined with both ultrasound-induced pressure and acoustic streaming mechanotransduction, is required to activate cultured cortical neurons. ASIC1a and cytoskeletal proteins were involved in the low-intensity ultrasound-mediated mechanotransduction and cultured neuron activation, which was inhibited by ASIC1a blockade and cytoskeleton-modified agents. In contrast, the inhibition of mechanical-sensitive channels involved in bilayer-model mechanotransduction like Piezo or TRP proteins did not repress the ultrasound-mediated neuronal activation as efficiently. The ASIC1a-mediated ultrasound effects in mouse brain such as immediate response of ERK phosphorylation and DCX marked neurogenesis were statistically significantly compromised by ASIC1a gene deletion. Collated data suggest that ASIC1a is the molecular determinant involved in the mechano-signaling of low-intensity ultrasound that modulates neural activation in mouse brain.

Low intensity ultrasound enhances cisplatin uptake in vitro by cochlear hair cells

Drug delivery to the inner ear has been challenging due to the blood-labyrinth barrier. Intracochlear drug delivery is an invasive alternative with less pharmacokinetic variables. In this study, the effect of low intensity ultrasound on drug uptake by hair cells is investigated. Cochlear explants harvested from newborn mice were cultured in a medium containing cisplatin to emulate drug delivered to the endolymph. The results demonstrated the exposure to ultrasound stimulation effectively enhanced cisplatin uptake by hair cells. The uptake started from the apical side of the hair cells and progressed inward as the exposure time increased.