Ca2+ signaling-mediated low-intensity pulsed ultrasound-induced proliferation and activation of motor neuron cells

Low-intensity pulsed ultrasound relieved the diabetic peripheral neuropathy in mice via anti-oxidative stress mechanism

Diabetic peripheral neuropathy (DPN), as one of the most prevalent complications of diabetes, leads to significant pain and financial burden to patients. Currently, there was no effective treatment for DPN since the glucose control was just a prevention and the drug therapy only relieved the DPN pain. As a non-invasive physical therapy, low-intensity pulsed ultrasound (LIPUS) is utilized in the musculoskeletal and nerve injuries therapy. Studies revealed that LIPUS could regenerate nerves by the mechanical stimulation via oxidative stress pathway, which was thought as the important factor for DPN, and might have potential in the DPN therapy. This study aimed to identify a new therapeutic strategy for DPN using LIPUS. We analyzed the therapy effect and explored the therapeutic mechanism of LIPUS on DPN in mice. This study involved animal experiments and C57BL/6J mice were randomly assigned to DPN model and Sham groups. The DPN model group was fed a high-fat chow diet and injected with streptozotocin (STZ) for 3 consecutive days (40 mg/kg/d), whereas the Sham group was fed a normal diet and injected with an equal volume of sodium citrate buffer. After the DPN model confirmed with the 84-day modeling process, the DPN mice were randomly allocated into the DPN group and the LIPUS group. The LIPUS group underwent ultrasound treatments with a center frequency of 1 MHz, a duty cycle of 20 %, and a spatial average temporal average intensity (ISATA) of 200 mW/cm2 for 20 min/d, 5 d/w. After the 56-day treatment, all mice were euthanized. LIPUS therapeutic effects were evaluated through measurements of fasting blood glucose (FBG), behavioral tests, oxidative stress tests, morphological analysis, immunofluorescence, and western blot analysis. The results indicated that DPN mice had significantly higher FBG levels (28.77 ± 2.95 mmol/L) compared with sham mice (10.31 ± 1.49 mmol/L). Additionally, DPN mice had significantly lower mechanical threshold (4.13 ± 0.92 g) and higher thermal latency (16.20 ± 2.39 s) compared with the sham mice (7.31 ± 0.83 g, 11.67 ± 1.21 s). After receiving LIPUS treatment, the glucose tolerance tests (GTT) suggested that LIPUS treatment improved glucose tolerance, which was shown by a decrease in the area under the curve (AUC) for glucose in the LIPUS group (AUC = 2452 ± 459.33 min*mmol/L) compared with the DPN group (AUC = 3271 ± 420.90 min*mmol/L). Behavioral tests showed that LIPUS treatment significantly alleviated DPN-induced abnormalities by improving the mechanical threshold from 2.79 ± 0.79 g in the DPN group to 5.50 ± 1.00 g in the LIPUS group, and significantly decreasing thermal latency from 12.38 ± 1.88 s in the DPN group to 9.49 ± 2.31 s in the LIPUS group. Morphological observations revealed that DPN mice had a thinning and irregularly shaped myelin sheath, with 61.04 ± 5.60 % of abnormal nerve fibers in the sciatic nerve in LIPUS group, compared with 49.76 ± 4.88 % of abnormal nerve fibers in the LIPUS-treated group. Additionally, LIPUS treatment increased the mean fluorescence intensity of the associated nerve regeneration protein (i.e., Nf200) from 27.81 ± 0.32 arbitrary units in the DPN group to 37.62 ± 0.36 arbitrary units in the LIPUS group. Western blot and immunofluorescence analysis showed that LIPUS treatment significantly reduced Keap1 expression to 0.04 ± 0.06 relative units, compared with 0.17 ± 0.30 in the DPN group. Furthermore, immunofluorescence analysis revealed that LIPUS treatment promoted the production of its downstream antioxidant protein, heme oxygenase-1 (HO-1), with an increase in the fluorescence intensity from 27.81 ± 0.32 arbitrary units in the DPN group to 37.62 ± 0.36 arbitrary units in the LIPUS-treated group. The fluorescence intensity of Nrf2 was significantly higher in the LIPUS group, increasing from 4.90 ± 0.25 arbitrary units in the DPN group to 15.18 ± 2.13 arbitrary units in the LIPUS-treated group. Additionally, the malondialdehyde (MDA) levels, an indicator of oxidative stress, were significantly reduced in the serum, from 5.40 ± 0.48 nmol/ml in the DPN group to 4.64 ± 0.16 nmol/ml in the LIPUS-treated group, and in the sciatic nerve, from 16.17 ± 5.88 nmol/mg protein to 4.67 ± 2.10 nmol/mg protein, suggesting the oxidative stress was inhibited by LIPUS. This study demonstrated for the first time that LIPUS could relive DPN through anti-oxidative stress process. This study suggests that LIPUS might be a new therapy strategy for DPN.

Low-intensity pulsed ultrasound promotes proliferation and differentiation of neural stem cells to enhance spinal cord injury recovery

BACKGROUND

Neural stem cells (NSCs) are known for their high capacity for proliferation, self-renewal, and multidirectional differentiation. However, they often fail to survive or differentiate into mature neurons capable of replacing lost neurons. This study evaluated the potential role of low-intensity pulsed ultrasound (LIPUS) in promoting NSC proliferation and differentiation both in vitro and in vivo, as well as its role in enhancing spinal cord injury (SCI) recovery.

METHODS

NSCs were isolated, stimulated with LIPUS, and characterized through identification and detection assays. The safety and efficacy of LIPUS in promoting NSC proliferation and differentiation were assessed through cell viability and apoptosis assays, and neuronal marker expression analysis. In vivo, NSCs encoding fluorescent proteins were transplanted into a rat model of SCI. The SCI rats received LIPUS for 4 weeks. Later, functional recovery, morphological changes and neuronal structures were evaluated.

RESULT

The isolated NSCs were successfully identified. LIPUS significantly enhanced NSC proliferation and increased the expression of key neurogenic markers and neurotrophic factors, while reducing GFAP expression and avoiding apoptosis. In vivo, the NSCs/LIPUS + group demonstrated higher survival and differentiation of transplanted NSCs, along with improved BBB scores and enhanced neural marker expression compared with the NSCs/LIPUS - group.

CONCLUSION

LIPUS stimulation effectively promoted NSC proliferation and differentiation and enhanced the survival and function of transplanted NSCs at the SCI site, leading to improved SCI recovery.

Low-intensity pulsed ultrasound reduces oxidative and endoplasmic reticulum stress in motor neuron cells

Endoplasmic reticulum (ER) stress is associated with oxidative stress, which is integral to the development of various pathological conditions, including neurodegenerative disorders. In this study, using NSC-34-a hybrid cell line established by fusing motor neuron-rich embryonic spinal cord cells with mouse neuroblastoma cells-we investigated the effects of low-intensity pulsed ultrasound (LIPUS) stimulation on oxidative (reactive oxygen species)/ER stress-induced neurodegeneration. An ultrasound transducer with a center frequency of 1.15 MHz and a spatial peak temporal average intensity of 357 mW/cm2 was used for delivering ultrasound (for 8 min, via a water-filled tube) to motor neuron cells seeded in a plastic culture dish. LIPUS stimulation significantly increased the level of the antiapoptotic protein B-cell lymphoma 2 (BCL-2) and inhibited the expression of apoptosis-associated proteins such as BCL-2-associated X protein (BAX), CCAAT/enhancer-binding protein-homologous protein (CHOP), and caspase-12, thus extending the survival of motor neurons. LIPUS stimulation also enhanced Ca2+ signaling and activated the Ca2+-dependent transcription factors as nuclear factor of activated T cells (NFAT) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Furthermore, LIPUS stimulation induced the activation of the serine/threonine kinase protein kinase B (AKT). Thus, LIPUS stimulation prevented oxidative/ER stress-mediated mitochondrial dysfunction. In conclusion, as a safe and noninvasive method, LIPUS stimulation can facilitate further development of ultrasound neuromodulation as a tool for neuroscience research.

L-Type Calcium Channel Modulates Low-Intensity Pulsed Ultrasound-Induced Excitation in Cultured Hippocampal Neurons

As a noninvasive technique, ultrasound stimulation is known to modulate neuronal activity both in vitro and in vivo. The latest explanation of this phenomenon is that the acoustic wave can activate the ion channels and further impact the electrophysiological properties of targeted neurons. However, the underlying mechanism of low-intensity pulsed ultrasound (LIPUS)-induced neuro-modulation effects is still unclear. Here, we characterize the excitatory effects of LIPUS on spontaneous activity and the intracellular Ca2+ homeostasis in cultured hippocampal neurons. By whole-cell patch clamp recording, we found that 15 min of 1-MHz LIPUS boosts the frequency of both spontaneous action potentials and spontaneous excitatory synaptic currents (sEPSCs) and also increases the amplitude of sEPSCs in hippocampal neurons. This phenomenon lasts for > 10 min after LIPUS exposure. Together with Ca2+ imaging, we clarified that LIPUS increases the [Ca2+]cyto level by facilitating L-type Ca2+ channels (LTCCs). In addition, due to the [Ca2+]cyto elevation by LIPUS exposure, the Ca2+-dependent CaMKII-CREB pathway can be activated within 30 min to further regulate the gene transcription and protein expression. Our work suggests that LIPUS regulates neuronal activity in a Ca2+-dependent manner via LTCCs. This may also explain the multi-activation effects of LIPUS beyond neurons. LIPUS stimulation potentiates spontaneous neuronal activity by increasing Ca2+ influx.

Repeated diagnostic ultrasound exposure modifies the structural properties of CA1 dendrites and alters the hippocampal transcriptome

The development of neurons is regulated by several spatiotemporally changing factors, which are crucial to give the ability of neurons to form functional networks. While external physical stimuli may impact the early developmental stages of neurons, the medium and long-term consequences of these influences have yet to be thoroughly examined. Using an animal model, this study focuses on the morphological and transcriptome changes of the hippocampus that may occur as a consequence of fetal ultrasound examination. We selectively labeled CA1 neurons of the hippocampus with in-utero electroporation to analyze their morphological features. Furthermore, certain samples also went through RNA sequencing after repetitive ultrasound exposure. US exposure significantly changed several morphological properties of the basal dendritic tree. A notable increase was also observed in the density of spines on the basal dendrites, accompanied by various alterations in individual spine morphology. Transcriptome analysis revealed several up or downregulated genes, which may explain the molecular background of these alterations. Our results suggest that US-derived changes in the dendritic trees of CA1 pyramidal cells might be connected to modification of the transcriptome of the hippocampus and may lead to an increased dendritic input.

Protective effects of low-intensity pulsed ultrasound (LIPUS) against cerebral ischemic stroke in mice by promoting brain vascular remodeling via the inhibition of ROCK1/p-MLC2 signaling pathway

Vascular remodeling is essential for patients with cerebral ischemic stroke (CIS). Our previous study proved that low-intensity pulsed ultrasound (LIPUS) could increase cortical hemodynamics. However, the effects and mechanisms of LIPUS on cerebral vascular remodeling after CIS are still unknown. In this study, we applied LIPUS to the mouse brain at 0.5 h after distal middle cerebral artery occlusion (dMCAO) and subsequently daily for a stimulation time of 30 min. Results showed that compared with the dMCAO group, LIPUS markedly increased cerebral blood flow (CBF), reduced brain swelling, and improved functional recovery at day 3 after CIS. LIPUS promoted leptomeningeal vasculature remodeling, enlarged vascular diameter, and increased the average vessel length and density at day 3 after CIS. Proteomic analysis highlighted that LIPUS mainly participated in the regulation of actin cytoskeleton pathway. Rho kinase 1 (ROCK1) was downregulated by LIPUS and participated in regulation of actin cytoskeleton. Subsequently, we verified that ROCK1 was mainly expressed in pericytes. Furthermore, we demonstrated that LIPUS inhibited ROCK1/p-MLC2 signaling pathway after CIS, which had positive effects on vascular remodeling and cerebral blood circulation. In conclusion, our preliminary study revealed the vascular remodeling effects and mechanism of LIPUS in CIS, provided evidence for potential clinical application of LIPUS.

Sonomechanobiology: Vibrational stimulation of cells and its therapeutic implications

All cells possess an innate ability to respond to a range of mechanical stimuli through their complex internal machinery. This comprises various mechanosensory elements that detect these mechanical cues and diverse cytoskeletal structures that transmit the force to different parts of the cell, where they are transcribed into complex transcriptomic and signaling events that determine their response and fate. In contrast to static (or steady) mechanostimuli primarily involving constant-force loading such as compression, tension, and shear (or forces applied at very low oscillatory frequencies (≤ 1 Hz) that essentially render their effects quasi-static), dynamic mechanostimuli comprising more complex vibrational forms (e.g., time-dependent, i.e., periodic, forcing) at higher frequencies are less well understood in comparison. We review the mechanotransductive processes associated with such acoustic forcing, typically at ultrasonic frequencies (> 20 kHz), and discuss the various applications that arise from the cellular responses that are generated, particularly for regenerative therapeutics, such as exosome biogenesis, stem cell differentiation, and endothelial barrier modulation. Finally, we offer perspectives on the possible existence of a universal mechanism that is common across all forms of acoustically driven mechanostimuli that underscores the central role of the cell membrane as the key effector, and calcium as the dominant second messenger, in the mechanotransduction process.

On minimal focal distance of a focused ultrasound probe for neuromodulation

Focal distance is a key parameter for a focused ultrasound probe, especially in mouse brain stimulation where targets are right below the skull. A closed-form solution for the minimal focal distance with a given transducer size was derived in this study to facilitate precise focal spot alignment with targets in the mouse brain. The spherical profile corresponding to the minimal focal distance does not produce accurate focusing. An iterative algorithm based on Snell's law was introduced for lens profile calculation. With a suitable step size, an accurate lens profile can be obtained for the minimal focal distance.

C. elegans: Sensing the low-frequency profile of amplitude-modulated ultrasound

Several research groups have demonstrated that C. elegans can respond to pulsed ultrasound stimuli, and elucidating the underlying mechanisms is necessary to develop ultrasound neuromodulation. Here, amplitude-modulated (AM) ultrasound is applied to C. elegans, and its behavioral responses are investigated in detail. By loading surface acoustic waves (SAWs) onto free-moving worms on an agar surface, a carrier wave with a frequency of 8.80 MHz is selected. The signal is modulated by a rectangular or sinusoidal profile. It is demonstrated that sinusoidal modulation can produce similar responses in worms to rectangular modulation, with the strongest responses occurring at modulation frequencies of around 1.00 kHz. Meanwhile, the behavioral response is relatively weak when the ultrasonic signal is unmodulated, that is, when only the carrier wave is applied. At modulation frequencies other than 100.00 Hz to 10.00 kHz, the worms respond weakly, but when a second modulation frequency of 1.00 kHz is introduced, an improvement in response can be observed. These results suggest that C. elegans may sense the low-frequency envelope and respond to amplitude-modulated ultrasonic stimuli like an amplitude demodulator. MEC-4, an ion channel for touch sensing, is involved in the behavioral response of C. elegans to ultrasound in the present setup.

Low intensity focused ultrasound: a new prospect for the treatment of Parkinson's disease

Background: As a chronic and progressive neurodegenerative disease, Parkinson's disease (PD) still lacks effective and safe targeted drug therapy. Low-intensity focused ultrasound (LIFU), a new method to stimulate the brain and open the blood-brain barrier (BBB), has been widely concerned by PD researchers due to its non-invasive characteristics.Methods: PubMed was searched for the past 10 years using the terms 'focused ultrasound', 'transcranial ultrasound', 'pulse ultrasound', and 'Parkinson's disease'. Relevant citations were selected from the authors' references. After excluding articles describing high-intensity focused ultrasound or non-Parkinson's disease applications, we found more than 100 full-text analyses for pooled analysis.Results: Current preclinical studies have shown that LIFU could improve PD motor symptoms by regulating microglia activation, increasing neurotrophic factors, reducing oxidative stress, and promoting nerve repair and regeneration, while LIFU combined with microbubbles (MBs) can promote drugs to cross the BBB, which may become a new direction of PD treatment. Therefore, finding an efficient drug carrier system is the top priority of applying LIFU with MBs to deliver drugs.Conclusions: This article aims to review neuro-modulatory effect of LIFU and the possible biophysical mechanism in the treatment of PD, summarize the latest progress in delivering vehicles with MBs, and discuss its advantages and limitations.