Role of uroguanylin's signalling pathway in the development of ischaemic stroke.

Stroke is one of the leading causes of mortality and disability worldwide. By affecting bradykinin function, activation of guanylate cyclase (GC)-A has been shown to have a neuroprotective effect after ischaemic stroke, whereas the same has not been confirmed for GC-B; therefore, we aimed to determine the possible role of GC-C and its agonist, uroguanylin (UGN), in the development of stroke. In this study, middle cerebral artery occlusion (MCAO) was performed on wild-type (WT), GC-C KO and UGN KO mice. MR images were acquired before and 24 h after MCAO. On brain slices 48 h after MCAO, the Ca2+ response to UGN stimulation was recorded. Our results showed that the absence of GC-C in GC-C KO mice resulted in the development of smaller ischaemic lesions compared with WT littermates, which is an opposite effect compared with the effects of GC-A agonists on brain lesions. WT and UGN KO animals showed a stronger Ca2+ response upon UGN stimulation in astrocytes of the peri-ischaemic cerebral cortex compared with the same cortical region of the unaffected contralateral hemisphere. This stronger activation was not observed in GC-C KO animals, which may be the reason for smaller lesion development in GC-C KO mice. The reason why GC-C might affect Ca2+ signalling in peri-ischaemic astrocytes is that GC-C is expressed in these cells after MCAO, whereas under normoxic conditions, it is expressed mainly in cortical neurons. Stronger activation of the Ca2+ -dependent signalling pathway could lead to the stronger activation of the Na+ /H+ exchanger, tissue acidification and neuronal death.

Novel micro-MRI approach for subchondral trabecular bone analysis in patients with hip osteoarthritis is comparable to micro-CT approach.

AIM: To test the agreement between a newly developed micro-magnetic resonance imaging (MRI) analysis of the subchondral bone and the micro-computed tomography (CT) approach. METHODS: Samples obtained from 10 patients with osteoarthritis undergoing total hip arthroplasty were scanned with a 7.0 T micro-MRI. Proton density-weighted images and proton density-weighted images with fat suppression were obtained. The results were validated with a micro-CT device. Micro-MRI and micro-CT scans of the same sample were aligned, and regions of interest were delineated on equal areas of the sample. Bone volume fraction was calculated by using in-house plugins. The agreement between the methods was tested with Bland-Altman analysis. RESULTS: The agreement between the methods was good, with average difference of 2.167%. The differences between the methods were not significant (P=0.272, t test). CONCLUSION: The novel micro-MRI approach could be used for subchondral bone analysis. With further optimization for clinical MRI machines, the approach can be also used in the diagnostics of hip osteoarthritis.

Activation of brown adipose tissue in diet-induced thermogenesis is GC-C dependent.

Uroguanylin (UGN) is released from the intestine after a meal. When applied in brain ventricles, UGN increases expression of markers of thermogenesis in brown adipose tissue (BAT). Therefore, we determine the effects of its receptor, guanylate cyclase C (GC-C), on mouse interscapular BAT (iBAT) activity during diet-induced thermogenesis (DIT). The activation of iBAT after a meal is diminished in GC-C KO mice, decreased in female wild type (WT) mice, and abolished in old WT animals. The activation of iBAT after a meal is the highest in male WT animals which leads to an increase in GC-C expression in the hypothalamus, an increase in iBAT volume by aging, and induction of iBAT markers of thermogenesis. In contrast to iBAT activation after a meal, iBAT activation after a cold exposure could still exist in GC-C KO mice and it is significantly higher in female WT mice. The expression of GC-C in the proopiomelanocortin neurons of the arcuate nucleus of the hypothalamus but not in iBAT suggests central regulation of iBAT function. The iBAT activity during DIT has significantly reduced in old mice but an intranasal application of UGN leads to an increase in iBAT activity in a dose-dependent manner which is in strong negative correlation to glucose concentration in blood. This activation was not present in GC-C KO mice. Our results suggest the physiological role of GC-C on the BAT regulation and its importance in the regulation of glucose homeostasis and the development of new therapy for obesity and insulin resistance.

Morphological maturation of the mouse brain: An in vivo MRI and histology investigation.

With the wide access to studies of selected gene expressions in transgenic animals, mice have become the dominant species as cerebral disease models. Many of these studies are performed on animals of not more than eight weeks, declared as adult animals. Based on the earlier reports that full brain maturation requires at least three months in rats, there is a clear need to discern the corresponding minimal animal age to provide an "adult brain" in mice in order to avoid modulation of disease progression/therapy studies by ongoing developmental changes. For this purpose, we have studied anatomical brain alterations of mice during their first six months of age. Using T2-weighted and diffusion-weighted MRI, structural and volume changes of the brain were identified and compared with histological analysis of myelination. Mouse brain volume was found to be almost stable already at three weeks, but cortex thickness kept decreasing continuously with maximal changes during the first three months. Myelination is still increasing between three and six months, although most dramatic changes are over by three months. While our results emphasize that mice should be at least three months old when adult animals are needed for brain studies, preferred choice of one particular metric for future investigation goals will result in somewhat varying age windows of stabilization.

suMRak: a multi-tool solution for preclinical brain MRI data analysis.

Introduction: Magnetic resonance imaging (MRI) is invaluable for understanding brain disorders, but data complexity poses a challenge in experimental research. In this study, we introduce suMRak, a MATLAB application designed for efficient preclinical brain MRI analysis. SuMRak integrates brain segmentation, volumetry, image registration, and parameter map generation into a unified interface, thereby reducing the number of separate tools that researchers may require for straightforward data handling. Methods and implementation: All functionalities of suMRak are implemented using the MATLAB App Designer and the MATLAB-integrated Python engine. A total of six helper applications were developed alongside the main suMRak interface to allow for a cohesive and streamlined workflow. The brain segmentation strategy was validated by comparing suMRak against manual segmentation and ITK-SNAP, a popular open-source application for biomedical image segmentation. Results: When compared with the manual segmentation of coronal mouse brain slices, suMRak achieved a high Sørensen-Dice similarity coefficient (0.98 ± 0.01), approaching manual accuracy. Additionally, suMRak exhibited significant improvement (p = 0.03) when compared to ITK-SNAP, particularly for caudally located brain slices. Furthermore, suMRak was capable of effectively analyzing preclinical MRI data obtained in our own studies. Most notably, the results of brain perfusion map registration to T2-weighted images were shown, improving the topographic connection to anatomical areas and enabling further data analysis to better account for the inherent spatial distortions of echoplanar imaging. Discussion: SuMRak offers efficient MRI data processing of preclinical brain images, enabling researchers' consistency and precision. Notably, the accelerated brain segmentation, achieved through K-means clustering and morphological operations, significantly reduces processing time and allows for easier handling of larger datasets.

Redefining the Koizumi model of mouse cerebral ischemia: A comparative longitudinal study of cerebral and retinal ischemia in the Koizumi and Longa middle cerebral artery occlusion models.

Cerebral and retinal ischemia share similar pathogenesis and epidemiology, each carrying both acute and prolonged risk of the other and often co-occurring. The most used preclinical stroke models, the Koizumi and Longa middle cerebral artery occlusion (MCAO) methods, have reported retinal damage with great variability, leaving the disruption of retinal blood supply via MCAO poorly investigated, even providing conflicting assumptions on the origin of the ophthalmic artery in rodents. The aim of our study was to use longitudinal in vivo magnetic resonance assessment of cerebral and retinal vascular perfusion after the ischemic injury to clarify whether and how the Koizumi and Longa methods induce retinal ischemia and how they differ in terms of cerebral and retinal lesion evolution. We provided anatomical evidence of the origin of the ophthalmic artery in mice from the pterygopalatine artery. Following the Koizumi surgery, retinal responses to ischemia overlapped with those in the brain, resulting in permanent damage. In contrast, the Longa method produced only extensive cerebral lesions, with greater tissue loss than in the Koizumi method. Additionally, our data suggests the Koizumi method should be redefined as a model of ischemia with chronic hypoperfusion rather than of ischemia and reperfusion.

Enhancing Functional Recovery Through Intralesional Application of Extracellular Vesicles in a Rat Model of Traumatic Spinal Cord Injury.

Local inflammation plays a pivotal role in the process of secondary damage after spinal cord injury. We recently reported that acute intravenous application of extracellular vesicles (EVs) secreted by human umbilical cord mesenchymal stromal cells dampens the induction of inflammatory processes following traumatic spinal cord injury. However, systemic application of EVs is associated with delayed delivery to the site of injury and the necessity for high doses to reach therapeutic levels locally. To resolve these two constraints, we injected EVs directly at the lesion site acutely after spinal cord injury. We report here that intralesional application of EVs resulted in a more robust improvement of motor recovery, assessed with the BBB score and sub-score, as compared to the intravenous delivery. Moreover, the intralesional application was more potent in reducing inflammation and scarring after spinal cord injury than intravenous administration. Hence, the development of EV-based therapy for spinal cord injury should aim at an early application of vesicles close to the lesion.

Nasal Chondrocyte-Based Engineered Grafts for the Repair of Articular Cartilage "Kissing" Lesions: A Pilot Large-Animal Study.

BACKGROUND: Bipolar or "kissing" cartilage lesions formed on 2 opposite articular surfaces of the knee joint are commonly listed as exclusion criteria for advanced cartilage therapies. PURPOSE: To test, in a pilot large-animal study, whether autologous nasal chondrocyte (NC)-based tissue engineering, recently introduced for the treatment of focal cartilage injuries, could provide a solution for challenging kissing lesions. STUDY DESIGN: Controlled laboratory study. METHODS: Osteochondral kissing lesions were freshly introduced into the knee joints of 26 sheep and covered with NC-based grafts with a low or high hyaline-like extracellular matrix; a control group was treated with a cell-free scaffold collagen membrane (SCA). The cartilage repair site was assessed at 6 weeks and 6 months after implantation by histology, immunohistochemistry, and magnetic resonance imaging evaluation. RESULTS: NC-based grafts, independently of their composition, induced partial hyaline cartilage repair with stable integrity in surrounding healthy tissue at 6 months after treatment. The SCA repaired cartilage to a similar degree to that of NC-based grafts. CONCLUSION: Kissing lesion repair, as evidenced in this sheep study, demonstrated the feasibility of the treatment of complex cartilage injuries with advanced biological methods. However, the potential advantages of an NC-based approach over a cell-free approach warrant further investigations in a more relevant preclinical model. CLINICAL RELEVANCE: NC-based grafts currently undergoing phase II clinical trials have a high potential to replace existing cartilage therapies that show significant limitations in the quality and reproducibility of the repair method. We have brought this innovative concept to the next level by addressing a new clinical indication.

Tlr2 Deficiency is Associated with Enhanced Elements of Neuronal Repair and Caspase 3 Activation Following Brain Ischemia.

The aim of this study was to apply multimodal in vivo imaging to assess the influence of altered innate immunity on brain repair after ischemic lesion. Tlr2-deficient mice were compared to wild type controls, as they lack Tlr2-mediated pro-inflammatory signaling triggered by postischemic necrosis. The ischemic lesion was induced by transient middle cerebral artery occlusion for 60 min, followed by brain imaging and analysis at four time points until 28 days after ischemia. Multimodal in vivo imaging involved a combination of 3 modalities: (1) magnetic resonance imaging by T2-weighted scans to assess brain lesion size, (2) bioluminescence imaging of Gap43-luc/gfp transgenic mice to visualize the axonal remodeling, and (3) caged-luciferin bioluminescence imaging of DEVD-luciferin allowing for visualization of caspase 3 and 7 activity in Gap43-luc/gfp mice. This enabled innovative correlation of the MRI-determined lesion size to photon fluxes obtained by bioluminescence imaging. Our data revealed that following ischemia, Tlr2-deficient mice had higher Gap43 expression and higher levels of caspases 3 and 7 activity, which was accompanied by enhanced levels of synaptic plasticity markers DLG4 and synaptophysin when compared to wild type controls. Altered inflammation in Tlr2-deficient mice was accompanied by enhanced elements of post-stroke repair, in particular during the chronic phase of recovery, but also with delayed final consolidation of the brain lesion.

D-mannose-Coating of Maghemite Nanoparticles Improved Labeling of Neural Stem Cells and Allowed Their Visualization by ex vivo MRI after Transplantation in the Mouse Brain.

Magnetic resonance imaging (MRI) of superparamagnetic iron oxide-labeled cells can be used as a non-invasive technique to track stem cells after transplantation. The aim of this study was to (1) evaluate labeling efficiency of D-mannose-coated maghemite nanoparticles (D-mannose(γ-Fe2O3)) in neural stem cells (NSCs) in comparison to the uncoated nanoparticles, (2) assess nanoparticle utilization as MRI contrast agent to visualize NSCs transplanted into the mouse brain, and (3) test nanoparticle biocompatibility. D-mannose(γ-Fe2O3) labeled the NSCs better than the uncoated nanoparticles. The labeled cells were visualized by ex vivo MRI and their localization subsequently confirmed on histological sections. Although the progenitor properties and differentiation of the NSCs were not affected by labeling, subtle effects on stem cells could be detected depending on dose increase, including changes in cell proliferation, viability, and neurosphere diameter. D-mannose coating of maghemite nanoparticles improved NSC labeling and allowed for NSC tracking by ex vivo MRI in the mouse brain, but further analysis of the eventual side effects might be necessary before translation to the clinic.