It is generally accepted that endothelial dysfunction precedes overt cardiovascular
disease and is a foundational event in development of atherosclerosis. Endothelial
function is often assessed by flow-mediated dilation (FMD), a physiological response to
shear stress along the endothelium that elicits vasodilation via release of nitric oxide
(NO) in large and small blood vessels. In the presence of Coronary Artery Disease (CAD),
NO production is reduced and FMD is diminished in conduit arteries. However, in the
microcirculation, FMD is preserved but there is a compensatory shift from NO to hydrogen
peroxide (H2O2) as the mediator of this dilation. The investigators lab has previously
identified several signaling pathways, including autophagy, that are involved in
regulating the switch in mechanism of dilation from NO to H2O2 utilizing ex vivo isolated
arteriole preparations in CAD. In this trial, the investigators explore the possible role
of autophagy as mechanism by which this switch occurs in a population at-risk for
cardiovascular disease. Macroautophagy (referred to as autophagy here forward) is a
scalable process designed to recycle damaged organelles via acidic hydrolases in
lysosomes to maintain homeostasis. The rationale for examining a role for autophagy stems
from data in cultured endothelial cells showing that autophagy can regulate NO
bioavailability and reactive oxygen species (ROS) production. Inhibition of key autophagy
proteins decreases NO production and increases ROS endothelial cells are exposed to shear
stress, markers of autophagy increase, along with a rise in NO production. The
investigators have recently demonstrated that autophagic flux is repressed in response to
shear stress in arterioles from patients with CAD compared to healthy controls. This
disease-associated reduction in autophagic flux increases release of H2O2 from the
mitochondria in response to shear stress. Activation or repression of autophagy in CAD
and healthy arterioles, respectively, switches the mechanism of dilation (activation in
CAD switches to NO; repression in healthy controls switches to H2O2). Collectively,
microvascular autophagic flux plays a key role integrating cellular signals within the
endothelium to regulate microvascular health and function in response to shear stress in
overt cardiovascular disease. The primary cellular mechanisms for this pathological
switch in in vasodilator mechanism and its relevance in other at-risk populations (e.g.,
type 2 diabetes mellitus; T2DM) remains unclear.
Hyperglycemia, Type 2 Diabetes Mellitus and Microvascular Function T2DM, a chronic
metabolic disease, is an independent risk factor for cardiovascular disease.
Hyperglycemia is a hallmark of T2DM, and both T2DM and hyperglycemia are independently
linked to endothelial dysfunction. While hyperglycemia in T2DM is often well-managed with
medication, damaging microvascular consequences such as diabetic neuropathy and
cardiomyopathy persist, and T2DM subjects demonstrate reduced microvascular
endothelial-dependent dilation. While ex vivo interrogation of vasodilator mechanisms
provides mechanistic insight into microvascular control, the lack of translation to in
vivo models represents a large gap in knowledge. The investigators have devised a
research strategy to directly study and fill this research gap, answering key questions
regarding the change in endothelial mediators that occurs with cardiovascular disease in
human tissue. T2DM and high glucose (HG) exposure are associated with reduced cutaneous
microvascular endothelial function ex vivo and in vivo. However, the mechanism by which
this reduction occurs is unclear. Furthermore, it is not known whether exposure to high
glucose alone, or the presence of T2DM are associated with a switch in the mechanism of
microvascular dilation to shear stress. Understanding and translating ex vivo findings to
in vivo settings will provide insight into the disease pathology and novel approaches to
ameliorate T2DM microvascular dysfunction.
Considering the important link between T2DM/HG-induced microvascular dysfunction and risk
of future cardiovascular events, stimulation of autophagic flux may enhance or preserve
available NO, exerting beneficial effects on microvascular function in patients with T2DM
and in response to HG. The purpose of this proposal is to investigate the fundamental
role of autophagy in contributing to T2DM microvascular dysfunction in a comprehensive
manner. The results of this study may inform the mechanistic understanding of
microvascular disease progression in T2DM.
Objective: Establish a mechanistic role for autophagic flux in contributing to
T2DM-associated microvascular dysfunction in vivo utilizing the human cutaneous
microcirculation as a novel translational model.
Hypothesis 1: Activation of autophagic flux with trehalose for 2 weeks in T2DM subjects
enhances cutaneous dilation to endothelial-dependent pharmacological agonists
(microdialysis) and local thermal hyperemia.
Hypothesis 2: Exposure to HG (oral glucose challenge) in healthy adults reduces cutaneous
dilation to endothelial-dependent pharmacological agonists and local thermal hyperemia.