The pathways by which mild hypothermia inhibits neuronal apoptosis following ischemia/reperfusion injury

Hypothermia improves neuronal network recovery in a human-derived in vitro model of oxygen-deprivation

Mild therapeutic hypothermia showed potential neuroprotective properties during and after cerebral hypoxia or ischemia in experimental animal studies. However, in clinical trials, where hypothermia is mainly applied after reperfusion, results were divergent and neurophysiological effects unclear. In our current study, we employed human-derived neuronal networks to investigate how treatment with hypothermia during hypoxia influences neuronal functionality and whether it improves post-hypoxic recovery. We differentiated neuronal networks from human induced pluripotent stem cells on micro-electrode arrays (MEAs). We studied the effect of hypothermia (34°C)-as well hyperthermia (39°C) - on neuronal functionality during and after hypoxia using MEAs. We also studied the effects on the number of synaptic puncta and cell viability by immunocytochemistry. In comparison to neuronal networks under normothermia, we found that hypothermia during hypoxia improved functional neuronal network recovery, expressed as enhanced neuronal network activity. This was associated with prevention of synaptic loss during and after the hypoxic phase. Furthermore, hypothermia improved cell viability after the hypoxic phase. Instead, hyperthermia during hypoxia had detrimental effects, with an irreversible loss of neuronal network function, loss of synaptic puncta and decreased cell viability. Our results show potential neuroprotective properties of hypothermia occurring during hypoxia, indicating that administering hypothermia to bridge the time to reperfusion may be beneficial in clinical settings.

Emerging Treatments for Subarachnoid Hemorrhage

The current landscape of therapeutic strategies for subarachnoid hemorrhage (SAH), a significant adverse neurological event commonly resulting from the rupture of intracranial aneurysms, is rapidly evolving. Through an in-depth exploration of the natural history of SAH, historical treatment approaches, and emerging management modalities, the present work aims to provide a broad overview of the shifting paradigms in SAH care. By synthesizing the historical management protocols with contemporary therapeutic advancements, patient-specific treatment plans can be individualized and optimized to deliver outstanding care for the best possible SAH-related outcomes.

Dynamic Culture of Mesenchymal Stromal/Stem Cell Spheroids and Secretion of Paracrine Factors

In recent years, conditioned medium (CM) obtained from the culture of mesenchymal stromal/stem cells (MSCs) has been shown to effectively promote tissue repair and modulate the immune response in vitro and in different animal models, with potential for application in regenerative medicine. Using CM offers multiple advantages over the implantation of MSCs themselves: 1) simpler storage, transport, and preservation requirements, 2) avoidance of the inherent risks of cell transplantation, and 3) potential application as a ready-to-go biologic product. For these reasons, a large amount of MSCs research has focused on the characterization of the obtained CM, including soluble trophic factors and vesicles, preconditioning strategies for enhancing paracrine secretion, such as hypoxia, a three-dimensional (3D) environment, and biochemical stimuli, and potential clinical applications. In vitro preconditioning strategies can increase the viability, proliferation, and paracrine properties of MSCs and therefore improve the therapeutic potential of the cells and their derived products. Specifically, dynamic cultivation conditions, such as fluid flow and 3D aggregate culture, substantially impact cellular behaviour. Increased levels of growth factors and cytokines were observed in 3D cultures of MSC grown on orbital or rotatory shaking platforms, in stirred systems, such as spinner flasks or stirred tank reactors, and in microgravity bioreactors. However, only a few studies have established dynamic culture conditions and protocols for 3D aggregate cultivation of MSCs as a scalable and reproducible strategy for CM production. This review summarizes significant advances into the upstream processing, mainly the dynamic generation and cultivation of MSC aggregates, for de CM manufacture and focuses on the standardization of the soluble factor production.

Therapeutic Hypothermia Inhibits the Classical Complement Pathway in a Rat Model of Neonatal Hypoxic-Ischemic Encephalopathy

OBJECTIVE

Complement activation is instrumental in the pathogenesis of Hypoxic-ischemic encephalopathy (HIE), a significant cause of neonatal mortality and disability worldwide. Therapeutic hypothermia (HT), the only available treatment for HIE, only modestly improves outcomes. Complement modulation as a therapeutic adjunct to HT has been considered, but is challenging due to the wide-ranging role of the complement system in neuroinflammation, homeostasis and neurogenesis in the developing brain. We sought to identify potential therapeutic targets by measuring the impact of treatment with HT on complement effector expression in neurons and glia in neonatal HIE, with particular emphasis on the interactions between microglia and C1q.

METHODS

The Vannucci model was used to induce HIE in term-equivalent rat pups. At P10-12, pups were randomly assigned to three different treatment groups: Sham (control), normothermia (NT), and hypothermia (HT) treatment. Local and systemic complement expression and neuronal apoptosis were measured by ELISA, TUNEL and immunofluorescence labeling, and differences compared between groups.

RESULTS

Treatment with HT is associated with decreased systemic and microglial expression of C1q, decreased systemic C5a levels, and decreased microglial and neuronal deposition of C3 and C9. The effect of HT on cytokines was variable with decreased expression of pro and anti-inflammatory effectors. HT treatment was associated with decreased C1q binding on cells undergoing apoptosis.

CONCLUSION

Our data demonstrate the extreme complexity of the immune response in neonatal HIE. We propose modulation of downstream effectors C3a and C5a as a therapeutic adjunct to HT to enhance neuroprotection in the developing brain.

The Effect of Therapeutic Mild Hypothermia on Brain Microvascular Endothelial Cells During Ischemia-Reperfusion Injury

BACKGROUND

To determine the cerebral protective effects of mild hypothermia (MH) on cerebral microcirculation.

METHODS

We established ischemia-reperfusion (I/R) injury and MH treatment models with rat brain microvascular endothelial cells (RBMECs) in vitro and examined the apoptotic changes. The cultured RBMECs were randomly divided into the control group, I/R group, and MH group, which was further divided into two subgroups: intra-ischemia hypothermia (IIH) and post-ischemia hypothermia (PIH). Cell morphological changes were assessed using fluorescence microscopy. Apoptotic rates were obtained by flow cytometry. Expressions of caspase-3, Bax, and Bcl-2 were analyzed by Western blot.

RESULTS

I/R injury in vitro induced apoptosis of RBMECs. The apoptotic rates in the control group, I/R group, and MH group were 0.13, 19.04, and 13.13%, respectively (P < 0.01). Compared with the I/R group, the MH group showed a significant decrease in the number of apoptotic cells, mainly in stage I apoptotic cells (P < 0.0083). The caspase-3 and Bax expressions were significantly enhanced (P < 0.05) in RBMECs after I/R injury, while substantial decreases in Bcl-2 expression were noted (P < 0.05). Following MH intervention, the increase in caspase-3 and Bax expression was suppressed (P < 0.05), while Bcl-2 expression significantly increased. The apoptotic rates or protein expressions between the two subgroups were not different significantly (P > 0.05).

CONCLUSIONS

These results indicate that MH could inhibit RBMEC apoptosis by preventing pro-apoptotic cells and early apoptotic cells from progressing to intermediate and advanced stages. This may be due to the effect of MH on I/R-induced apoptotic gene expression changes.

Mild hypothermia protects hippocampal neurons from oxygen-glucose deprivation injury through inhibiting caspase-3 activation

Mild hypothermia (MH) is thought to be one of the most effective therapeutic methods to treat hypoxic-ischemic encephalopathy (HIE) after cardiac arrest (CA). However, its precise mechanisms remain unclear. In this research, hippocampal neurons were cultured and treated with mild hypothermia and Ac-DEVD-CHO after oxygen-glucose deprivation (OGD). The activity of caspase-3 was detected, in order to find the precise concentration of Ac-DEVD-CHO with the same protective role in OGD injury as MH treatment. Western blot and immunofluorescence staining were conducted to analyze the effects of MH and Ac-DEVD-CHO on the expressions of caspase-3, caspase-8, and PARP. The neuronal morphology was observed with an optical microscope. The lactic acid dehydrogenase (LDH) release rate, neuronal viability, and apoptotic rate were also detected. We found that MH (32 °C) and Ac-DEVD-CHO (5.96 μMol/L) had equal effects on blocking the activation of caspase-3 and the OGD-induced cleavage of PARP, but neither had any effect on the activation of caspase-8, which goes on to activate caspase-3 in the apoptotic pathway. Meanwhile, both MH and Ac-DEVD-CHO had similar effects in protecting cell morphology, reducing LDH release, and inhibiting OGD-induced apoptosis in neurons. They also similarly improved neuronal viability after OGD. In conclusion, caspase-3 serves as a key intervention point of the key modulation site or regulatory region in MH treatment that protects neuronal apoptosis against OGD injury. Inhibiting the expression of caspase-3 had a protective effect against OGD injury in MH treatment, and caspase-3 activation could be applied to evaluate the neuroprotective effectiveness of MH on HIE.

Mild hypothermia protects against oxygen glucose deprivation/reoxygenation-induced apoptosis via the Wnt/β-catenin signaling pathway in hippocampal neurons

Mild hypothermia is thought to be one of the most effective therapies for cerebral ischemia/reperfusion injuries. Our previous research revealed that mild hypothermia inhibits the activation of caspase-3 and protects against oxygen glucose deprivation/reoxygenation (OGD/R)-induced injury in hippocampal neurons. However, the mechanisms behind the activation of caspase-3 remain unclear. The aims of this study were to determine whether the protective effects of mild hypothermia were exerted through the Wnt/β-catenin signaling pathway. We found that, under OGD/R conditions, the pathway was down regulated, but mild hypothermia induced the reactivation of the Wnt/β-catenin signaling pathway, which had been suppressed by OGD/R injury. Mild hypothermia also caused the down regulation of the expression of apoptosis promoting proteins (Bax cleaved caspase-3), up-regulated the expression of apoptosis inhibiting proteins (Bcl-2), and ameliorated OGD/R injury-induced apoptosis. The protective effects of mild hypothermia were blocked by DKK1 (an antagonist of the canonical Wnt signaling pathway). Taken together, these results indicate that the Wnt/β-catenin signaling pathway mediates the protective effects of mild hypothermia against OGD/R-induced apoptosis. Our study provides evidence that mild hypothermia reactivates the Wnt/β-catenin signaling pathway, which is suppressed by OGD/R injury, in hippocampal neurons and protects neurons from OGD/R-induced apoptosis via the reactivation of the Wnt/β-catenin signaling pathway, ultimately suggesting that mild hypothermia could have therapeutic effects on OGD/R-induced apoptosis.

Hypothermia reduces VEGF-165 expression, but not osteogenic differentiation of human adipose stem cells under hypoxia

Cryotherapy is successfully used in the clinic to reduce pain and inflammation after musculoskeletal damage, and might prevent secondary tissue damage under the prevalent hypoxic conditions. Whether cryotherapy reduces mesenchymal stem cell (MSC) number and differentiation under hypoxic conditions, causing impaired callus formation is unknown. We aimed to determine whether hypothermia modulates proliferation, apoptosis, nitric oxide production, VEGF gene and protein expression, and osteogenic/chondrogenic differentiation of human MSCs under hypoxia. Human adipose MSCs were cultured under hypoxia (37°C, 1% O2), hypothermia and hypoxia (30°C, 1% O2), or control conditions (37°C, 20% O2). Total DNA, protein, nitric oxide production, alkaline phosphatase activity, gene expression, and VEGF protein concentration were measured up to day 8. Hypoxia enhanced KI67 expression at day 4. The combination of hypothermia and hypoxia further enhanced KI67 gene expression compared to hypoxia alone, but was unable to prevent the 1.2-fold reduction in DNA amount caused by hypoxia at day 4. Addition of hypothermia to hypoxic cells did not alter the effect of hypoxia alone on BAX-to-BCL-2 ratio, alkaline phosphatase activity, gene expression of SOX9, COL1, or osteocalcin, or nitric oxide production. Hypothermia decreased the stimulating effect of hypoxia on VEGF-165 gene expression by 6-fold at day 4 and by 2-fold at day 8. Hypothermia also decreased VEGF protein expression under hypoxia by 2.9-fold at day 8. In conclusion, hypothermia decreased VEGF-165 gene and protein expression, but did not affect differentiation, or apoptosis of MSCs cultured under hypoxia. These in vitro results implicate that hypothermia treatment in vivo, applied to alleviate pain and inflammation, is not likely to harm early stages of callus formation.