Tag: Ashley Walker

The effects of ovariectomy and soy diet on vascular function in female C57BL6 mice

Presenter: Aleena Khurana − Human Physiology

Faculty Mentor(s): Ashley Walker, Mackenzie Kehmeier

Session: (In-Person) Oral Panel—Stimuli and Response

As people begin to live longer, studying age-related disease becomes more important. Age is a major risk factor for Alzheimer’s disease (AD), a prominent neurodegenerative disease, and other cardiovascular diseases; Females develop AD at much higher rates and all signs point to sex hormones. Estrogen drastically decreases post menopause, and it has been suggested that estrogen deficiency is a contributing factor to the sex differences seen in AD and other age-related diseases. The vascular system plays an important role in aging. A characteristic of aging in the vascular system is stiffening of larger arteries. Large artery stiffening is detrimental due to the increase in pulse pressure and stress associated with stiffening. Decreased estrogen activity results in increased production of reactive oxygen species (ROS), causing tissue damage and dysfunction. Elevated ROS and oxidative stress increase inflammation in the brain, further explaining the potential effects estrogen loss has in relation to such diseases. Soy also has been seen to be a protective factor against symptoms of age-related disease due to its role as a phytoestrogen, thus showing the potential importance of soy. This study aimed to explore the effects of estrogen depletion post menopause and the effects of a soy diet in relation with estrogen loss. We utilized a mouse model including ovariectomies to mimic estrogen loss post menopause and studied cognitive function, motor coordination, and vascular function.

In vivo arterial stiffness, but not endothelial function, varies with the mouse estrus cycle

Presenter: Bradley Bedell − Multidisciplinary Science

Faculty Mentor(s): Mackenzie Kehmeier MS, Ashley Walker PhD

(In-Person) Poster Presentation 

Historically, females have been omitted from research due to their perceived variability. Hormones fluctuate throughout the estrus cycle in mice mimicking the human menstrual cycle. The endothelium plays a role in vascular function and arterial stiffness. Human endothelial function and arterial stiffness vary throughout the menstrual cycle, however this has yet to be investigated in the mouse model.

C56Bl/6J mouse estrus cycle stage was identified via vaginal cytology prior to testing. Arterial stiffness was assessed via aortic pulse wave velocity. Endothelial function and nitric oxide mediated dilation were assessed by dose responses in pressurized mesenteric (MA) and posterior cerebral arteries (PCAs). Gene expression in PCAs and MAs was assessed as well as aortic protein analysis.

Aortic pulse wave velocity was lowered for mice in estrus as compared to diestrus. PCA and MCA dose responses did not differ between stages of the estrus cycle. PCA Esr2 gene coding for estrogen receptor β (ERβ) expression was lowered for mice in estrus as compared to diestrus and proestrus.

The estrus phase in mice is associated with lower in vivo large artery stiffness. There were no differences between the estrus cycle phase in ex vivo resistance artery endothelial function. ER gene expression changes during the estrus cycle are limited to ERβ in the cerebral arteries. These results suggest that estrus phase should be considered when measuring in vivo arterial stiffness in young female mice.

The Effect of Pyridoxamine on Ages and Aortic Wall Structure

Presenter(s): Elise Kronquist

Faculty Mentor(s): Ashley Walker

Oral Session 1 C

Aging leads to arterial stiffening, likely due to increased advanced glycation end products (AGEs), oxidative stress, and collagen, which contribute to vascular dysfunction. Pyridoxamine, a form of vitamin B6, prevents age-related arterial stiffening. We hypothesized that pyridoxamine treatment will prevent AGEs formation in aged mouse aortas, while not affecting aortic wall structure.

Eight aged C57BL6 mice (18 mo) were treated with pyridoxamine in their water for six months and compared with eight vehicle control old mice (normal drinking water, 18 mo) and 6 untreated young mice (6 mo). Histological samples were collected. Aorta samples were quantified for AGEs via immunofluorescence. Aorta samples were also stained with Verheoff-Van Gieson and wall area was measured.

Young mice trended toward fewer AGEs than old control mice in the aorta (0.01 ± 0.003 vs 0.1 ± 0.05 AU), but the pyridoxamine treated animals were not different than old control or young mice (0.05 ± 0.02; p=0.11). The overall thickness of the aortic wall was unchanged between young, old treated, and old control subjects (area: 25840 ± 3388μm^2 vs. 34617 ± 5232μm^2 vs. 34165 ± 3377μm^2; p=0.3). Treatment did not change adventitial thickness between young, old control, and old treated groups (area: 21352 ± 2695μm^2 vs. 26102 ± 5006μm^2 vs. 30099 ± 4587μm^2; p=0.4).

These results indicate pyridoxamine treatment does not prevent the formation of AGEs or change the wall structure of the aorta in aged mice. Further studies are needed to identify the mechanism by which pyridoxamine prevents age-related arterial stiffening.

Robo4 Project

Presenter(s): Byron Lee—Human Physiology

Faculty Mentor(s): Ashley Walker

Session 6: Interact & React

Aging is associated with the impairment of the neurovascular unit, and this potentially leads to increased Alzheimer’s disease pathology and cognitive impairment . A specific axon guidance receptor, Robo4, is important in maintaining the structure and restrictive barrier of the blood-brain barrier (BBB) . We predicted that the knockout of Robo4, and the subsequent increase in BBB permeability, will result in cognitive dysfunction . Therefore, Robo4 signaling pathways may potentially be a valuable target for therapeutic treatments of AD . In the present study, we studied Robo4 knockout (Robo4 -/-) and wild type (Robo4 +/+) mice crossed with mice containing mutations in amyloid precursor protein (APP), leading to greater aberrant amyloid-beta production . To examine the effect of aging, we studied young and old wildtype C57BL6 mice . We assessed cognitive function by conducting Nest Building tests and Morris Water Maze . We found that old C57BL6 mice had impaired cognitive function compared to young C57BL6 mice . However, when Robo4 x APP groups were compared, we found no differences in cognitive function . These preliminary results suggest that aging has a stronger effect on cognitive function than Robo4 knockout . Additional studies are needed to determine the effect of Robo4 knockout on blood-brain barrier permeability and amyloid-beta accumulation .

Association between a non-invasive assessment of frailty and vascular dysfunction in old mice

Presenter(s): Jazmin Cole—Human Physiology, Biology

Faculty Mentor(s): Ashley Walker

Session 6: Interact & React

Advancing age is characterized by not only an increased risk for cardiovascular diseases (CVDs), but also a decline in functional reserve and impaired adaptive capacity across multiple physiologic systems, also known as frailty . Impaired vascular function is a known contributor to CVDs and potentially has a role in increased frailty . In patients with overt disease, measures of frailty are related to vascular endothelial cell dysfunction . However, the relation between vascular endothelial function and frailty in a non-disease population is unknown .

To examine the relation between vascular function and frailty in the context of similar genetics and environment, we studied wildtype C57BL/6 mice . In young (9 mo, n=7) and old (23-30 mo, n=27) male and female mice, we assessed endothelial-dependent dilation (EDD) ex vivo in isolated, pressurized mesentery arteries and middle cerebral arteries (MCA) . Mouse frailty was assessed using a previously established non-invasive 31-item frailty index based on clinical signs of deterioration . The severity of each deficit was assessed by two independent observers and assigned a value between 0-1, with a higher score indicating more severe frailty .

Frailty index was ~6 fold greater in old compared with young mice (p<0 .001) . Among the old mice, frailty index was correlated with mesentery artery maximal EDD (r=-0 .53 p=0 .002), and remained significant after controlling for age (partial correlation: r=-0 .38, p=0 .03) .

This study demonstrates that frailty, independent of age, is associated with mesentery artery endothelial dysfunction in wildtype, non-diseased mice . However, it remains unknown whether the mesentery artery dysfunction is a cause or consequence of the greater frailty . Interestingly, we found a lack of association between frailty and cerebral artery endothelial function . Future research is needed to determine the mechanisms linking frailty and mesentery artery dysfunction .