Ageing and chronic intermittent hypoxia mimicking sleep apnea do not modify local brain tissue stiffness in healthy mice

Measuring ventral nerve cord stiffness in live flat-dissected Drosophila embryos by atomic force microscopy

Drosophila is an amenable system for addressing the mechanics of morphogenesis. We describe a workflow for characterizing the mechanical properties of its ventral nerve cord (VNC), at different developmental stages, in live, flat-dissected embryos employing atomic force microscopy (AFM). AFM is performed with spherical probes, and stiffness (Young's modulus) is calculated by fitting force curves with Hertz's contact model. For complete details on the use and execution of this protocol, please refer to Karkali et al. (2022).

Biomechanical characteristics of the ovarian cortex in POI patients and functional outcomes after drug-free IVA

PURPOSE

There is increasing evidence that the ovarian extracellular matrix (ECM) plays a critical role in follicle development. The rigidity of the cortical ECM limits expansion of the follicle and consequently oocyte maturation, maintaining the follicle in its quiescent state. Quiescent primordial, primary, and secondary follicles still exist in primary ovarian insufficiency (POI) patients, and techniques as in vitro activation (IVA) and drug-free IVA have recently been developed aiming to activate these follicles based on the Hippo signaling disruption that is essential in mechanotransduction. In this context, we analyze the effect of drug-free IVA in POI patients, comparing the relationship between possible resumption ovarian function and biomechanical properties of ovarian tissue.

METHODS

Nineteen POI patients according to ESHRE criteria who underwent drug-free IVA by laparoscopy between January 2018 and December 2019 and were followed up for a year after the intervention. A sample of ovarian cortex taken during the intervention was analyzed by atomic force microscopy (AFM) in order to quantitatively measure tissue stiffness (Young's elastic modulus, E) at the micrometer scale. Functional outcomes after drug-free were analyzed.

RESULTS

Resumption of ovarian function was observed in 10 patients (52.6%) and two of them became pregnant with live births. There were no differences in clinical characteristics (age and duration of amenorrhea) and basal hormone parameters (FSH and AMH) depending on whether or not there was activation after surgery. However, ovarian cortex stiffness was significantly greater in patients with ovarian activity after drug-free IVA: median E = 5519 Pa (2260-11,296) vs 1501 (999-3474); p-value < 0.001.

CONCLUSIONS

Biomechanical properties of ovarian cortex in POI patients have a great variability, and higher ovarian tissue stiffness entails a more favorable status when drug-free IVA is applied in their treatment. This status is probably related to an ovary with more residual follicles, which would explain a greater possibility of ovarian follicular reactivations after treatment.

Hypoxia and brain aging: Neurodegeneration or neuroprotection?

The absolute reliance of the mammalian brain on oxygen to generate ATP renders it acutely vulnerable to hypoxia, whether at high altitude or in clinical settings of anemia or pulmonary disease. Hypoxia is pivotal to the pathogeneses of myriad neurological disorders, including Alzheimer's, Parkinson's and other age-related neurodegenerative diseases. Conversely, reduced environmental oxygen, e.g. sojourns or residing at high altitudes, may impart favorable effects on aging and mortality. Moreover, controlled hypoxia exposure may represent a treatment strategy for age-related neurological disorders. This review discusses evidence of hypoxia's beneficial vs. detrimental impacts on the aging brain and the molecular mechanisms that mediate these divergent effects. It draws upon an extensive literature search on the effects of hypoxia/altitude on brain aging, and detailed analysis of all identified studies directly comparing brain responses to hypoxia in young vs. aged humans or rodents. Special attention is directed toward the risks vs. benefits of hypoxia exposure to the elderly, and potential therapeutic applications of hypoxia for neurodegenerative diseases. Finally, important questions for future research are discussed.

Sleep Apnea Syndrome in an Elderly Population Admitted to a Geriatric Unit: Prevalence and Effect on Cognitive Function

Background

Sleep apnea leads to cognitive impairment in older patients, but its association with neurodegeneration remains controversial, and most studies do not distinguish between the more common obstructive form (OSAS) and the rarer central form (CSAS).

Objective

The purpose of this study was to assess the prevalence of the different forms of sleep apnea in a cohort of cognitively impaired elderly patients (>70 years) and to investigate their associations with cognitive deficit, weighted against known risk factors for neurodegeneration.

Methods

Overnight polygraphy was performed for 76 consecutive patients admitted to our geriatric unit. Their cognitive function was assessed using the Mini Mental-State Exam (MMSE), Mattis Dementia Rating Scale (MDRS) and Stroop test. Multivariable analyses were performed to determine associations between cognitive function and independent variables describing demographics, sleep apnea measures, and cardiovascular risk factors.

Results

The cohort comprised 58 women and 18 men aged a mean of 84 years (range, 73-96). Sleep apnea syndrome (SAS) was diagnosed in 48 patients (63%), of which 31 (41%) with OSAS and 17 (22%) with CSAS. Multivariable regression analysis revealed that MDRS was lower in patients with OSAS (β = -10.03, p = 0.018), that Stroop Colors and Words delays increased with AHI (β = 0.17, p = 0.030 and β = 0.31, p = 0.047) and that that Stroop Interference delay was higher in patients with CSAS (β = 24.45, p = 0.002).

Conclusion

Sleep apnea is thus highly prevalent in elderly patients with cognitive impairment. OSAS was associated with lower general cognitive function, while CSAS was only associated with increased Stroop Interference delays. Elderly patients with cognitive deficit could benefit from sleep apnea screening and treatment.

Characterization of the elastic properties of extracellular matrix models by atomic force microscopy

Tissue elasticity is a critical regulator of cell behavior in normal and diseased conditions like fibrosis and cancer. Since the extracellular matrix (ECM) is a major regulator of tissue elasticity and function, several ECM-based models have emerged in the last decades, including in vitro endogenous ECM, decellularized tissue ECM and ECM hydrogels. The development of such models has urged the need to quantify their elastic properties particularly at the nanometer scale, which is the relevant length scale for cell-ECM interactions. For this purpose, the versatility of atomic force microscopy (AFM) to quantify the nanomechanical properties of soft biomaterials like ECM models has emerged as a very suitable technique. In this chapter we provide a detailed protocol on how to assess the Young's elastic modulus of ECM models by AFM, discuss some of the critical issues, and provide troubleshooting guidelines as well as illustrative examples of AFM measurements, particularly in the context of cancer.

The impact of obstructive sleep apnea and PAP therapy on all-cause and cardiovascular mortality based on age and gender - a literature review

BACKGROUND

Obstructive sleep apnea (OSA) is a common sleep disorder which negatively impacts different body systems, especially the cardiovascular system. The correlation between sleep related breathing disorders and cardiovascular diseases has been well studied. However, the impact of OSA on cardiovascular related mortality and the role of positive airway pressure therapy in decreasing mortality is unclear. We reviewed studies investigating the impact of OSA on all-cause and cardiovascular related mortality in both genders, and in different age groups.

METHODS

A literature search (PubMed) using two phrases "obstructive sleep apnea and co-morbidities in males and females" and "obstructive sleep apnea and co-morbidities by age" yielded a total of 214 articles. Nineteen articles met the inclusion criteria.

RESULTS

The studies reviewed showed conflicting results. Some showed that OSA increases all cause and cardiovascular related mortality predominantly in the middle-aged group (40-65) followed by a plateau or a reduction in mortality. Other studies showed a positive linear correlation between OSA and mortality up to the age of 80. The same controversy was noted for gender; some studies did not observe an increase in mortality in females with OSA, while others observed a trend for an increase in mortality in females.

CONCLUSION

There is a debate in the literature regarding the impact of OSA on all-cause and cardiovascular mortality in both genders and in different age groups. However, the variation in results might be related to different study designs and significant epidemiological prevalence of OSA in males and females.

Alzheimer's Disease Mutant Mice Exhibit Reduced Brain Tissue Stiffness Compared to Wild-type Mice in both Normoxia and following Intermittent Hypoxia Mimicking Sleep Apnea

Background

Evidence from patients and animal models suggests that obstructive sleep apnea (OSA) may increase the risk of Alzheimer's disease (AD) and that AD is associated with reduced brain tissue stiffness.

Aim

To investigate whether intermittent hypoxia (IH) alters brain cortex tissue stiffness in AD mutant mice exposed to IH mimicking OSA.

Methods

Six-eight month old (B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J) AD mutant mice and wild-type (WT) littermates were subjected to IH (21% O₂ 40 s to 5% O₂ 20 s; 6 h/day) or normoxia for 8 weeks. After euthanasia, the stiffness (E) of 200-μm brain cortex slices was measured by atomic force microscopy.

Results

Two-way ANOVA indicated significant cortical softening and weight increase in AD mice compared to WT littermates, but no significant effects of IH on cortical stiffness and weight were detected. In addition, reduced myelin was apparent in AD (vs. WT), but no significant differences emerged in the cortex extracellular matrix components laminin and glycosaminoglycans when comparing baseline AD and WT mice.

Conclusion

AD mutant mice exhibit reduced brain tissue stiffness following both normoxia and IH mimicking sleep apnea, and such differences are commensurate with increased edema and demyelination in AD.

Influence of hippocampal niche signals on neural stem cell functions during aging

The genesis of new neurons from neural stem cells in the adult brain offers the hope that this mechanism of plasticity can be harnessed for the treatment of brain injuries and diseases. However, neurogenesis becomes impaired during the normal course of aging; this is also the primary risk factor for most neurodegenerative diseases. The local microenvironment that regulates the function of resident neural stem cells (the "neurogenic niche") is a particularly complex network of various signaling mechanisms, rendering it especially challenging for the dissection of the control of these cells but offering the potential for the advancement of our understanding of the regulation/misregulation of neurogenesis. In this review, we examine the factors that control neurogenesis in an age-dependent manner, and we define these signals by the extrinsic mechanism through which they are presented to the neural stem cells. Secreted signals, cell-contact-dependent signals, and extracellular matrix cues all contribute to the regulation of the aging neurogenic niche and offer points of therapeutic intervention.