Sex differences in sleep apnea and comorbid neurodegenerative diseases

Chronic intermittent hypoxia attenuates noradrenergic innervation of hypoglossal motor nucleus

The state-dependent noradrenergic activation of hypoglossal motoneurons plays an important role in the maintenance of upper airway patency and pathophysiology of obstructive sleep apnea (OSA). Chronic intermittent hypoxia (CIH), a major pathogenic factor of OSA, contributes to the risk for developing neurodegenerative disorders in OSA patients. Using anterograde tracer, channelrhodopsin-2, we mapped axonal projections from noradrenergic A7 and SubCoeruleus neurons to hypoglossal nucleus in DBH-cre mice and assessed the effect of CIH on these projections. We found that CIH significantly reduced the number of axonal projections from SubCoeruleus neurons to both dorsal (by 68%) and to ventral (by73%) subregions of the hypoglossal motor nucleus compared to sham-treated animals. The animals' body weight was also negatively affected by CIH. Both effects, the decrease in axonal projections and body weight, were more pronounced in male than female mice, which was likely caused by less sensitivity of female mice to CIH as compared to males. The A7 neurons appeared to have limited projections to the hypoglossal nucleus. Our findings suggest that CIH-induced reduction of noradrenergic innervation of hypoglossal motoneurons may exacerbate progression of OSA, especially in men.

The influence of social support on sleep and fatigue level among patients receiving hemodialysis in Saudi Arabia: a cross-sectional correlational design

Background

Patients on hemodialysis (HD) are more likely to experience sleep problems and fatigue that may affect their health outcomes. Management of these patients with social support may improve their sleep quality and fatigue as well as their health.

Aim

This study aimed to assess the influence of social support on sleep quality and fatigue levels among HD patients.

Methods

A cross-correlational study was conducted among 260 conveniently sampled HD patients from four dialysis centers in Hail and Al-Qassim cities of Saudi Arabia from Jun 2022 to January 2023. Besides sociodemographic data, the Pittsburgh Sleep Quality Index (PSQI), the Multidimensional Assessment of Fatigue (MAF) and the Oslo Social Support Scale (OSSS-3) were used to assess sleep quality, fatigue levels and social support, respectively. Chi-square test was used to determine the association between categorical variables, while Pearson's correlation coefficient was used to test the correlation between sleep quality, fatigue, and social support.

Results

Poor sleep and high fatigue were significantly higher in older patients compared to younger patients (p <0.001), while strong social support was significantly lower in older patients than younger and middle-aged ones (p = 0.001). On the other hand, poor sleep and high fatigue were significantly higher in males than females (p = 0.022 and p <0.001, respectively), while strong social support was significantly higher in females than males (p <0.001). Married patients showed significantly poorer sleep than single ones (p = 0.019), but single patients received significantly stronger social support. Retired patients showed significantly poorer sleep, higher fatigue and weaker social support than other groups (p <0.001). There was a significant negative correlation between fatigue and sleep quality among HD patients, where patients with more fatigue had poorer sleep (r = -0.510, p <0.001). A significant positive correlation was found between social support and sleep quality, where patients with stronger social support had more normal sleep (r = 0.415, p <0.001). However, a significant negative correlation was found between social support and fatigue, where patients with stronger social support had lower levels of fatigue (r = -0.479, p <0.001).

Conclusion

Saudi patients on HD who have stronger social support have better sleep quality and reduced fatigue levels than those with less social support. There is a need to design and implement intervention studies with structured social support programs, and to evaluate their effectiveness on improving sleep and reducing fatigue among HD patients.

Overall Obesity Not Abdominal Obesity Has a Causal Relationship with Obstructive Sleep Apnea in Individual Level Data

Objective

Both obstructive sleep apnea (OSA) and obesity are highly prevalent worldwide, and are intrinsically linked. Previous studies showed that obesity is one of the major risk factors for OSA, but the causality of the relationship is still unclear. The study was to investigate the causal relationships of overall obesity and abdominal obesity with OSA and its quantitative traits.

Methods

In this case-control study, a total of 7134 participants, including 4335 moderate-to-severe OSA diagnosed by standard polysomnography and 2799 community-based controls were enrolled. Anthropometric and biochemical data were collected. Mendelian randomization (MR) analyses were performed using the genetic risk score, based on 29 body mass index (BMI)- and 11 waist-hip-ratio (WHR)-associated single nucleotide polymorphisms as instrumental variables. The causal associations of these genetic scores with OSA and its quantitative phenotypes were analyzed.

Results

Obesity was strongly correlated with OSA in observational analysis (β= 0.055, P = 3.7 × 10-5). In MR analysis, each increase by one standard deviation in BMI was associated with increased OSA risk [odds ratio (OR): 2.21, 95% confidence interval (CI): 1.62-3.02, P = 5.57 × 10-7] and with 2.72-, 4.68-, and 3.25-fold increases in AHI, ODI, and MAI, respectively (all P < 0.05) in men. However, no causal associations were found between WHR and OSA risk or OSA quantitative traits in men and women.

Conclusion

Compared to abdominal obesity, overall obesity showed a causal relationship with OSA and its quantitative traits, especially in men.

Sleep Quality and Its Affecting Factors among Hemodialysis Patients: A Multicenter Cross-Sectional Study

(1) Background: Sleep quality is one of the most important clinical outcomes of hemodialysis (HD) patients, as it can affect their physical and mental health. This study aimed to investigate sleep quality and its affecting factors among patients with HD. (2) Methods: A cross-sectional design was used to investigate the quality of sleep among HD patients in two cities in Saudi Arabia. The data were collected during the period from January to December 2022. A convenience sample of 250 HD patients was selected in this study. Data were collected using the Arabic version of the Pittsburgh Sleep Quality Index (PSQI). (3) Results: About two-thirds of participants (63.6%) had normal sleep, while one-third had poor sleep (36.4%). There was a significant relationship between the participants' age and the quality of sleep, where participants who were aged more than 50 had poorer sleep than those who were younger (p < 0.001). Male and married participants significantly had poor sleep more than female and single participants (p = 0.011 and 0.015, respectively). In addition, participants who were retired, had a higher number of dependents, did not adhere to exercise, and had more comorbidities had significantly poorer sleep than other groups (p = 0.002, 0.016, 0.023, and <0.001, respectively). The level of education, financial status, distance from home to dialysis center, and participants' satisfaction at the time of dialysis had no influence on the quality of sleep among HD patients. The multiple linear regression shows that exercise (p = 0.017), the number of comorbidities (p = 0.008), and the duration of dialysis (p < 0.020) were the independent factors affecting the quality of sleep among HD patients. (4) Conclusions: About one-third of HD patients in this study had poor sleep. There were significant differences between patients' age, gender, marital status, and sleep-quality levels. Moreover, participants who retired, had a higher number of dependents, did not adhere to exercise, and had more comorbidities had significantly poorer sleep than other groups. Future studies should develop appropriate interventions to address the problem of poor sleep quality among HD patients.

Sleep quality and sleep duration predict brain microstructure among community-dwelling older adults

Although poor sleep quality and extreme sleep durations have been associated with brain atrophy and dementia, it is unclear whether sleep disturbances contribute to neural injury in the absence of neurodegeneration and cognitive impairment. In 146 dementia-free older adults of the Rancho Bernardo Study of Healthy Aging (76.7 ± 7.8 years at MRI), we examined associations of restriction spectrum imaging metrics of brain microstructure with self-reported sleep quality 6.3 ± 0.7 years prior, and with sleep duration reported 25, 15 and 9 years prior. Worse sleep quality predicted lower white matter restricted isotropic diffusion and neurite density and higher amygdala free water, with stronger associations between poor sleep quality and abnormal microstructure for men. Among women only, short or long sleep duration 25 and 15 years before MRI predicted lower white matter restricted isotropic diffusion and increased free water. Associations persisted after accounting for associated health and lifestyle factors. Sleep patterns were not related to brain volume or cortical thickness. Optimizing sleep behaviors throughout the life-course may help to preserve healthy brain aging.

Hospital-diagnosed sleep disorders and incident dementia: a nationwide observational cohort study

BACKGROUND AND PURPOSE

Several smaller, community-based studies have suggested a link between sleep disorders and dementia with a focus on sleep as a modifiable risk factor for dementia. Studies on neurodegenerative diseases are prone to reverse causation, and few studies have examined the association with long follow-up time. Our aim was to explore the possible association between sleep disorders and late-onset dementia in an entire population.

METHODS

In a nationwide cohort with 40-year follow-up, associations between hospital-based sleep disorder diagnoses and late-onset dementia were assessed. Incidence rate ratios (IRR) were calculated using Poisson regression.

RESULTS

The cohort consisted of 1,491,276 people. Those with any sleep disorder had a 17% higher risk of dementia (IRR 1.17, 95% confidence interval [CI] 1.11-1.24) compared to people with no sleep disorder, adjusted for age, sex, calendar year, highest attained educational level at age 50, and somatic and psychiatric comorbidity. The risk of dementia was significantly increased 0-5 years after sleep disorder diagnosis (IRR 1.35, 95% CI 1.25-1.47), whilst the association after 5 years or more was non-significant (1.05, 95% CI 0.97-1.13).

CONCLUSIONS

Our findings show an increased short-term risk of dementia following a hospital-based sleep disorder diagnosis, whilst weaker evidence of a long-term risk was found. This could potentially point towards sleep disorders as an early symptom of dementia. Further research is needed to distinguish sleep disorders as an early symptom of dementia, a risk factor, or both.

Female specific risk factors for the development of Alzheimer's disease neuropathology and cognitive impairment: Call for a precision medicine approach

Alzheimer's disease (AD) includes a long asymptomatic stage, which precedes the formal diagnosis of dementia. AD biomarker models provide a framework for precision medicine approaches during this stage. However, such approaches have ignored the possible influence of sex on cognition and brain health, despite female sex noted as a major risk factor. Since AD-related changes may emerge in midlife, intervention efforts are being redirected around this period. Midlife coincides with several endocrinological changes, such as the menopausal transition experienced by women. In this narrative review, we discuss evidence for sex-differences in AD neuropathological burden and outline key endocrinological mechanisms for both sexes, focussing on hormonal events throughout the lifespan that may influence female susceptibility to AD neuropathology and dementia onset. We further consider common non-modifiable (genetic) and modifiable (lifestyle and health) risk factors, highlighting possible sex-dependent differential effects for the AD disease course. Finally, we evaluate the studies selected for this review demonstrating sex-differences in cognitive, pathological and health factors, summarising the state of sex differences in AD risk factors. We further provide recommendations for targeted research on female-specific risk factors, to inform personalised strategies for AD-prevention and the promotion of female brain health.

Alzheimer's Disease, Sleep Disordered Breathing, and Microglia: Puzzling out a Common Link

Sleep Disordered Breathing (SDB) and Alzheimer's Disease (AD) are strongly associated clinically, but it is unknown if they are mechanistically associated. Here, we review data covering both the cellular and molecular responses in SDB and AD with an emphasis on the overlapping neuroimmune responses in both diseases. We extensively discuss the use of animal models of both diseases and their relative utilities in modeling human disease. Data presented here from mice exposed to intermittent hypoxia indicate that microglia become more activated following exposure to hypoxia. This also supports the idea that intermittent hypoxia can activate the neuroimmune system in a manner like that seen in AD. Finally, we highlight similarities in the cellular and neuroimmune responses between SDB and AD and propose that these similarities may lead to a pathological synergy between SDB and AD.

Stress and Loss of Ovarian Function: Novel Insights into the Origins of Sex-Based Differences in the Manifestations of Respiratory Control Disorders During Sleep

The respiratory system of women and men develops and functions in distinct neuroendocrine milieus. Despite differences in anatomy and neural control, homeostasis of arterial blood gases is ensured in healthy individuals regardless of sex. This convergence in function differs from the sex-based differences observed in many respiratory diseases. Sleep-disordered breathing (SDB) results mainly from episodes of upper airway closure. This complex and multifactorial respiratory disorder shows significant sexual dimorphism in its clinical manifestations and comorbidities. Guided by recent progress from basic research, this review discusses the hypothesis that stress is necessary to reveal the sexual dimorphism of SDB.

LncRNA XIST promotes inflammation by downregulating GRα expression in the adenoids of children with OSAHS

Whether glucocorticoid receptor α (GRα) serves a role in obstructive sleep apnea/hypopnea syndrome (OSAHS) remains unclear. However, it has been reported that GRα expression is decreased in the adenoids of patients with OSAHS. The present study aimed to evaluate the role of GRα in OSAHS and the underlying mechanism. Bioinformatics assays revealed that long noncoding RNA (lncRNA) X inactivate-specific transcript (XIST) was closely associated with GRα. Furthermore, reverse transcription-quantitative PCR showed that the expression of lncRNA XIST was significantly increased in the adenoids of patients with OSAHS compared with healthy controls. Further in vitro studies by Pearson correlation analysis, RNA pull-down assay, western blot analysis and ELISA demonstrated that XIST significantly decreased the expression of GRα and that significantly increased the production of inflammatory cytokines, including interleukin (IL)-8, tumor necrosis factor α, IL-6 and IL-1β, while the overexpression of GRα significantly decreased the production of these inflammatory cytokines in NP69 cells, a human nasopharyngeal epithelial cell line. Furthermore, XIST significantly increased the protein levels of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) subunits, including Rel-B, c-Rel, P52, P50 and P65, which are associated with the transcription of cytokines. The stimulatory effect of XIST was significantly inhibited by the NF-κB inhibitor EVP4593. These results indicated that the stimulatory effect of XIST was dependent on NF-κB. In summary, the present study demonstrated that the XIST-GRα-NF-κB signaling pathway contributed to inflammation in the adenoids of patients with OSAHS.

Simulated sleep apnea alters hydrogen sulfide regulation of blood flow and pressure

In sleep apnea, airway obstruction causes intermittent hypoxia (IH). In animal studies, IH-dependent hypertension is associated with loss of vasodilator hydrogen sulfide (H₂S), and increased H₂S activation of sympathetic nervous system (SNS) activity in the carotid body. We previously reported that inhibiting cystathionine γ-lyase (CSE) to prevent H₂S synthesis augments vascular resistance in control rats. The goal of this study was to evaluate the contribution of IH-induced changes in CSE signaling to increased blood pressure and vascular resistance. We hypothesized that chronic IH exposure eliminates CSE regulation of blood pressure (BP) and vascular resistance. In rats instrumented with venous catheters, arterial telemeters, and flow probes on the main mesenteric artery, the CSE inhibitor dl-propargylglycine (PAG, 50 mg/kg/day i.v. for 5 days) increased BP in Sham rats but decreased BP in IH rats [in mmHg, Sham (n = 11): 114 ± 4 to 131 ± 6; IH (n = 8): 131 ± 8 to 115 ± 7 mmHg, P < 0.05]. PAG treatment increased mesenteric vascular resistance in Sham rats but decreased it in IH rats (day 5/day 1: Sham: 1.50 ± 0.07; IH: 0.85 ± 0.19, P < 0.05). Administration of the ganglionic blocker hexamethonium (to evaluate SNS activity) decreased mesenteric resistance in PAG-treated Sham rats more than in saline-treated Sham rats or PAG-treated IH rats. CSE immunoreactivity in IH carotid bodies compared with those from Sham rats. However, CSE staining in small mesenteric arteries was less in arteries from IH than in Sham rats but not different in larger arteries (inner diameter > 200 µm). These results suggest endogenous H₂S regulates blood pressure and vascular resistance, but this control is lost after IH exposure with decreased CSE expression in resistance size arteries. IH exposure concurrently increases carotid body CSE expression and relative SNS control of blood pressure, suggesting both vascular and carotid body H₂S generation contribute to blood pressure regulation.NEW & NOTEWORTHY These results suggest that CSE's protective role in the vasculature is impaired by simulated sleep apnea, which also upregulates CSE in the carotid body. Thus, this enzyme system can exert both pro- and antihypertensive effects and may contribute to elevated SNS outflow in sleep apnea.

Sex and age differentially affect GABAergic neurons in the mouse prefrontal cortex and hippocampus following chronic intermittent hypoxia

Obstructive sleep apnea (OSA), a chronic sleep disorder characterized by repetitive reduction or cessation of airflow during sleep, is widely prevalent and is associated with adverse neurocognitive sequelae including increased risk of Alzheimer's disease (AD). In humans, OSA is more common in elderly males. OSA is characterized by sleep fragmentation and chronic intermittent hypoxia (CIH), and recent epidemiological studies point to CIH as the best predictor of neurocognitive sequelae associated with OSA. The sex- and age- specific effects of OSA-associated CIH on specific cell populations such as γ-aminobutyric acid (GABA)-ergic neurons in the hippocampus and the medial prefrontal cortex (mPFC), regions important for cognitive function, remain largely unknown. The present study examined the effect of 35 days of either moderate (10% oxygen) or severe (5% oxygen) CIH on GABAergic neurons in the mPFC and hippocampus of young and aged male and female mice as well as post-accelerated ovarian failure (AOF) female mice. In the mPFC and hippocampus, the number of GABA-labeled neurons increased in aged and young severe CIH males compared to controls but not in young moderate CIH males. This change was not representative of the individual GABAergic cell subpopulations, as the number of parvalbumin-labeled neurons decreased while the number of somatostatin-labeled neurons increased in the hippocampus of severe CIH young males only. In all female groups, the number of GABA-labeled cells was not different between CIH and controls. However, in the mPFC, CIH increased the number of parvalbumin-labeled neurons in young females and the number of somatostatin-labeled cells in AOF females but decreased the number of somatostatin-labeled cells in aged females. In the hippocampus, CIH decreased the number of somatostatin-labeled neurons in young females. CIH decreased the density of vesicular GABA transporter in the mPFC of AOF females only. These findings suggest sex-specific changes in GABAergic neurons in the hippocampus and mPFC with males showing an increase of this cell population as compared to their female counterparts following CIH. Age at exposure and severity of CIH also differentially affect the GABAergic cell population in mice.

Diabetes, a Contemporary Risk for Parkinson's Disease: Epidemiological and Cellular Evidences

Diabetes mellitus (DM), a group of diseases characterized by defective glucose metabolism, is the most widespread metabolic disorder affecting over 400 million adults worldwide. This pathological condition has been implicated in the pathogenesis of a number of central encephalopathies and peripheral neuropathies. In further support of this notion, recent epidemiological evidence suggests a link between DM and Parkinson’s disease (PD), with hyperglycemia emerging as one of the culprits in neurodegeneration involving the nigrostriatal pathway, the neuroanatomical substrate of the motor symptoms affecting parkinsonian patients. Indeed, dopaminergic neurons located in the mesencephalic substantia nigra appear to be particularly vulnerable to oxidative stress and degeneration, likely because of their intrinsic susceptibility to mitochondrial dysfunction, which may represent a direct consequence of hyperglycemia and hyperglycemia-induced oxidative stress. Other pathological pathways induced by increased intracellular glucose levels, including the polyol and the hexosamine pathway as well as the formation of advanced glycation end-products, may all play a pivotal role in mediating the detrimental effects of hyperglycemia on nigral dopaminergic neurons. In this review article, we will examine the epidemiological as well as the molecular and cellular clues supporting the potential susceptibility of nigrostriatal dopaminergic neurons to hyperglycemia.

Beneficial effects of estrogens in obstructive sleep apnea hypopnea syndrome

Epidemiological studies showing the higher frequency of obstructive sleep apnea hypopnea syndrome in men, polycystic ovary syndrome (PCOS), and in post-menopausal women suggest the beneficial role of estrogen. These findings are well supported by the pre-clinical studies (ten research studies described in this review) showing that estrogen and phytoestrogens attenuate the deleterious effects of chronic intermittent hypoxia (obstructive apnea in animals) on the genioglossal muscles and on other organs (co-morbidities) in ovariectomized rodents. Moreover, clinical studies (four research studies described in this review) have also shown the beneficial role of estrogen therapy on the parameters of obstructive apnea in post-menopausal women. The beneficial effects of estrogen and phytoestrogens on obstructive sleep apnea and its co morbidities have been attributed to increase in thioredoxin, Nrf-2, activation of p38 MAP kinases, inhibition of vagal C fibers, and attenuation of HIF-1α. It is possible that estrogen-mediated activation of p38 MAP kinase may inhibit HIF-1α to attenuate lung inflammation, which may inhibit the activation of vagal C fibers to attenuate bronchoconstriction and prevent obstruction during sleep. Moreover, estrogen-mediated increase in thioredoxin and Nrf-2 may also contribute in increasing antioxidant defense and attenuating inflammation.

Androgens modulate chronic intermittent hypoxia effects on brain and behavior

Sleep apnea is associated with testosterone dysregulation as well as increased risk of developing neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). A rodent model of the hypoxemic events of sleep apnea, chronic intermittent hypoxia (CIH), has been previously documented to impair cognitive function and elevate oxidative stress in male rats, while simultaneously decreasing testosterone. Therefore, androgens may modulate neuronal function under CIH. To investigate the role of androgens during CIH, male rats were assigned to one of four hormone groups: 1) gonadally intact, 2) gonadectomized (GDX), 3) GDX + testosterone (T) supplemented, or 4) GDX + dihydrotestosterone (DHT) supplemented. Each group was exposed to either normal room air or CIH exposure for one week, followed by memory and motor task assessments. Brain regions associated with AD and PD (entorhinal cortex, dorsal hippocampus, and substantia nigra) were examined for oxidative stress and inflammatory markers, key characteristics of AD and PD. Gonadally intact rats exhibited elevated oxidative stress due to CIH, but no significant memory and motor impairments. GDX increased memory impairments, regardless of CIH exposure. T preserved memory function and prevented detrimental CIH-induced changes. In contrast, DHT was not protective, as evidenced by exacerbated oxidative stress under CIH. Further, CIH induced significant spatial memory impairment in rats administered DHT. These results indicate androgens can have both neuroprotective and detrimental effects under CIH, which may have clinical relevance for men with untreated sleep apnea.