Normobaric intermittent hypoxic training regulates microglia phenotype and enhances phagocytic activity

Intermittent hypoxic training - derived exosomes in stroke rehabilitation

Ischemic stroke is the fourth leading cause of adult disability in the US, and it is a huge social burden all over the world. However, the efficient treatment of ischemic stroke is not available. An apparent reason for failing to find or develop an intervention for ischemic stroke is contributed to the tight blood-brain barrier (BBB). The unique characteristics of exosomes that can traverse BBB have been highlighted among researchers investigating interventions for ischemic stroke conditions. Additionally, intermittent hypoxic training has been considered a potential intervention in the treatment or rehabilitation process of ischemic stroke patients. In this mini-review, we are going to review the possibility of applying exosomes produced by a subject who does intermittent hypoxic conditioning in a treatment program for ischemic stroke.

Assessing the importance and safety of hypoxia conditioning for patients with occupational pulmonary diseases: A recent clinical perspective

Occupational pulmonary diseases (OPDs) pose a significant global health challenge, contributing to high mortality rates. This review delves into the pathophysiology of hypoxia and the safety of intermittent hypoxic conditioning (IHC) in OPD patients. By examining sources such as PubMed, Relemed, NLM, Scopus, and Google Scholar, the review evaluates the efficacy of IHC in clinical outcomes for OPD patients. It highlights the complexities of cardiovascular and respiratory regulation dysfunctions in OPDs, focusing on respiratory control abnormalities and the impact of intermittent hypoxic exposures. Key areas include the physiological effects of hypoxia, the role of hypoxia-inducible factor-1 alpha (HIF-1α) in occupational lung diseases, and the links between brain ischemia, stroke, and OPDs. The review also explores the interaction between intermittent hypoxic exposures, mitochondrial energetics, and lung physiology. The potential of IHE to improve clinical manifestations and underlying pathophysiology in OPD patients is thoroughly examined. This comprehensive analysis aims to benefit molecular pathologists, pulmonologists, clinicians, and physicians by enhancing understanding of IHE's clinical benefits, from research to patient care, and improving clinical outcomes for OPD patients.

Advancing stroke recovery: unlocking the potential of cellular dynamics in stroke recovery

Stroke stands as a predominant cause of mortality and morbidity worldwide, and there is a pressing need for effective therapies to improve outcomes and enhance the quality of life for stroke survivors. In this line, effective efferocytosis, the clearance of apoptotic cells, plays a crucial role in neuroprotection and immunoregulation. This process involves specialized phagocytes known as "professional phagocytes" and consists of four steps: "Find-Me," "Eat-Me," engulfment/digestion, and anti-inflammatory responses. Impaired efferocytosis can lead to secondary necrosis and inflammation, resulting in adverse outcomes following brain pathologies. Enhancing efferocytosis presents a potential avenue for improving post-stroke recovery. Several therapeutic targets have been identified, including osteopontin, cysteinyl leukotriene 2 receptor, the µ opioid receptor antagonist β-funaltrexamine, and PPARγ and RXR agonists. Ferroptosis, defined as iron-dependent cell death, is now emerging as a novel target to attenuate post-stroke tissue damage and neuronal loss. Additionally, several biomarkers, most importantly CD163, may serve as potential biomarkers and therapeutic targets for acute ischemic stroke, aiding in stroke diagnosis and prognosis. Non-pharmacological approaches involve physical rehabilitation, hypoxia, and hypothermia. Mitochondrial dysfunction is now recognized as a major contributor to the poor outcomes of brain stroke, and medications targeting mitochondria may exhibit beneficial effects. These strategies aim to polarize efferocytes toward an anti-inflammatory phenotype, limit the ingestion of distressed but viable neurons, and stimulate efferocytosis in the late phase of stroke to enhance post-stroke recovery. These findings highlight promising directions for future research and development of effective stroke recovery therapies.

Intermittent hypoxia training enhances Aβ endocytosis by plaque associated microglia via VPS35-dependent TREM2 recycling in murine Alzheimer's disease

BACKGROUND

Beta-amyloid (Aβ) deposition in the brain parenchyma is a crucial initiating step in the amyloid cascade hypothesis of Alzheimer's disease (AD) pathology. Furthermore, dysfunction of plaque-associated microglia, also known as disease-associated microglia (DAM) has been reported to accelerate Aβ deposition and cognitive impairment. Our previous research demonstrated that intermittent hypoxia training (IHT) improved AD pathology by upregulating autophagy in DAM, thereby enhancing oligomeric Aβ (oAβ) clearance. Considering that oAβ internalization is the initial stage of oAβ clearance, this study focused on the IHT mechanism involved in upregulating Aβ uptake by DAM.

METHODS

IHT was administered to 8-month-old APP/PS1 mice or 6-month-old microglial vacuolar protein sorting 35 (VPS35) knockout mice in APP/PS1 background (MG VPS35 KO: APP/PS1) for 28 days. After the IHT, the spatial learning-memory capacity of the mice was assessed. Additionally, AD pathology was determined by estimating the nerve fiber and synapse density, Aβ plaque deposition, and Aβ load in the brain. A model of Aβ-exposed microglia was constructed and treated with IHT to explore the related mechanism. Finally, triggering receptor expressed on myeloid cells 2 (TREM2) intracellular recycling and Aβ internalization were measured using a fluorescence tracing technique.

RESULTS

Our results showed that IHT ameliorated cognitive function and Aβ pathology. In particular, IHT enhanced Aβ endocytosis by augmenting the intracellular transport function of microglial TREM2, thereby contributing to Aβ clearance. Furthermore, IHT specifically upregulated VPS35 in DAM, the primary cause for the enhanced intracellular recycling of TREM2. IHT lost ameliorative effect on Aβ pathology in MG VPS35 KO: APP/PS1 mice brain. Lastly, the IHT mechanism of VPS35 upregulation in DAM was mediated by the transcriptional regulation of VPS35 by transcription factor EB (TFEB).

CONCLUSION

IHT enhances Aβ endocytosis in DAM by upregulating VPS35-dependent TREM2 recycling, thereby facilitating oAβ clearance and mitigation of Aβ pathology. Moreover, the transcriptional regulation of VPS35 by TFEB demonstrates a close link between endocytosis and autophagy in microglia. Our study further elucidates the IHT mechanism in improving AD pathology and provides evidence supporting the potential application of IHT as a complementary therapy for AD.

Microglia-mediated neuroinflammation and neuroplasticity after stroke

Stroke remains a major cause of long-term disability and mortality worldwide. The immune system plays an important role in determining the condition of the brain following stroke. As the resident innate immune cells of the central nervous system, microglia are the primary responders in a defense network covering the entire brain parenchyma, and exert various functions depending on dynamic communications with neurons, astrocytes, and other neighboring cells under both physiological or pathological conditions. Microglia activation and polarization is crucial for brain damage and repair following ischemic stroke, and is considered a double-edged sword for neurological recovery. Microglia can exist in pro-inflammatory states and promote secondary brain damage, but they can also secrete anti-inflammatory cytokines and neurotrophic factors and facilitate recovery following stroke. In this review, we focus on the role and mechanisms of microglia-mediated neuroinflammation and neuroplasticity after ischemia and relevant potential microglia-based interventions for stroke therapy.

Intermittent hypoxia promotes the recovery of motor function in rats with cerebral ischemia by regulating mitochondrial function

Hypoxia preconditioning is neuroprotective, but the therapeutic effects of intermittent hypoxia were not fully considered. The present study investigated the neuroprotective effect and mechanism of intermittent hypoxia on motor function after cerebral ischemia and explored alternative clinical treatment options. In total, 36 8-week-old male Sprague-Dawley rats were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO) and then randomly divided into a sham-operated group (SHAM), tMCAO-sedentary group (SED), and tMCAO-intermittent hypoxia group (IH). The intervention was performed 1 week after tMCAO and lasted 4 weeks. Rats in the IH group were placed in an animal hypoxic chamber (altitude 5000 m and oxygen concentration of 13%) for 4 h/day and 7 days/week, and rats in the SED group were placed in a normoxic environment for 4 weeks. Body weights, neurological deficit scores, cerebral infarction volume ratios, gait analyses, mitochondrial structure, adenosine triphosphate (ATP) content and AMO-activated protein kinase (AMPK), peroxisome proliferator-activated receptor γ co-activator-1α (PGC-1α), and silencing regulatory protein 3 (Sirt3) expression in the peri-ischemic region brain tissues were detected during the intervention. Compared with the SED group, the body weight of the IH group gradually recovered, and the neurological deficit scores were significantly reduced (P < 0.05). The gait analysis results showed that the pressure of the affected paw and the maximum content area, swing speed, stride length, and other parameters were significantly restored (P < 0.05). The cerebral infarction volume ratio was significantly reduced (P < 0.01). Mitochondrial morphological structure damage in the peri-ischemic region brain tissues recovered, the number was significantly increased (P < 0.05), and the expression of AMPK, PGC-1α, and Sirt3 proteins (P < 0.05), and ATP content were significantly increased (P < 0.05). Intermittent hypoxia may activate the AMPK-PGC-1α-Sirt3 signaling pathway, promote mitochondrial biogenesis, repair mitochondrial ultrastructural damage, and improve mitochondrial function to reduce brain damage and promote motor function recovery in rats with cerebral ischemia.

Effects of Intermittent Hypoxia in Training Regimes and in Obstructive Sleep Apnea on Aging Biomarkers and Age-Related Diseases: A Systematic Review

Several studies have assessed the effects of intermittent hypoxia-normoxia training (IHNT), intermittent hypoxia-hyperoxia training (IHHT), and obstructive sleep apnea (OSA) on aging and age-related diseases in humans; however, the results remain contradictory. Therefore, this review aims to systematically summarize the available studies on the effects of IHNT, IHHT, and OSA on aging and age-related diseases. Relevant studies were searched from PubMed, Google Scholar, Cochrane Library databases, and through manual searching from reference lists of eligible studies. A total of 38 eligible studies were included in this systematic review. IHHT and IHNT provide positive effects on several age-related parameters including quality of life, cognitive and physical functions, plasma level of glucose and cholesterol/LDL, systolic blood pressure, red blood cells, and inflammation. Moreover, moderate intermittent hypoxia induces telomerase reverse transcriptase (TERT) activity and telomere stabilization, delays induction of senescence-associated markers expression and senescence-associated β-galactosidase, upregulates pluripotent marker (Oct4), activates a metabolic shift, and raises resistance to pro-apoptotic stimuli. On the contrary, intermittent hypoxia in OSA causes hypertension, metabolic syndrome, vascular function impairment, quality of life and cognitive scores reduction, advanced brain aging, increase in insulin resistance, plasma hydrogen peroxide, GSH, IL-6, hsCRP, leptin, and leukocyte telomere shortening. Thus, it can be speculated that the main factor that determines the direction of the intermittent hypoxia action is the intensity and duration of exposure. There is no direct study to prove that IHNT/IHHT actually increases life expectancy in humans. Therefore, further study is needed to investigate the actual effect of IHNT/IHHT on aging in humans.

Systematic Review Registration

www.crd.york.ac.uk/prospero, identifier CRD42022298499.

Hypoxia/ischemia impairs CD33 (Siglec-3)/TREM2 signaling: Potential role in Alzheimer's pathogenesis

Recent genetic and molecular studies have indicated that the innate immune system, especially microglia, have a crucial role in the accumulation of β-amyloid plaques in Alzheimer's disease (AD). In particular, the CD33 receptor, also called Siglec-3, inhibits the TREM2 receptor-induced phagocytic activity of microglia. CD33 receptors recognize the α2,3 and α2,6-linked sialic groups in tissue glycocalyx, especially sialylated gangliosides in human brain. The CD33 receptor triggers cell-type specific responses, e.g., in microglia, CD33 inhibits phagocytosis, whereas in natural killer cells, it inhibits the cytotoxic activity of the NKG2D receptor. Nonetheless, the regulation of the activity of CD33 receptor needs to be clarified. For example, it seems that hypoxia/ischemia, a potential cause of AD pathology, increases the expression of CD33 and its downstream target SHP-1, a tyrosine phosphatase which suppresses the phagocytosis driven by TREM2. Moreover, hypoxia/ischemia increases the deposition of sialylated gangliosides, e.g., GM1, GM2, GM3, and GD1, which are ligands for inhibitory CD33/Siglec-3 receptors. In addition, β-amyloid peptides bind to the sialylated gangliosides in raft-like clusters and subsequently these gangliosides act as seeds for the formation of β-amyloid plaques in AD pathology. It is known that senile plaques contain sialylated GM1, GM2, and GM3 gangliosides, i.e., the same species induced by hypoxia/ischemia treatment. Sialylated gangliosides in plaques might stimulate the CD33/Siglec-3 receptors of microglia and thus impede TREM2-driven phagocytosis. We propose that hypoxia/ischemia, e.g., via the accumulation of sialylated gangliosides, prevents the phagocytosis of β-amyloid deposits by inhibiting CD33/TREM2 signaling.