Regulation of blood flow in small arteries: mechanosensory events underlying myogenic vasoconstriction

Harnessing the benefits of glycine supplementation for improved pancreatic microcirculation in type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is predominantly managed using insulin replacement therapy, however, pancreatic microcirculatory disturbances play a critical role in T1DM pathogenesis, necessitating alternative therapies. This study aimed to investigate the protective effects of glycine supplementation on pancreatic microcirculation in T1DM. Streptozotocin-induced T1DM and glycine-supplemented mice (n = 6 per group) were used alongside control mice. Pancreatic microcirculatory profiles were determined using a laser Doppler blood perfusion monitoring system and wavelet transform spectral analysis. The T1DM group exhibited disorganized pancreatic microcirculatory oscillation. Glycine supplementation significantly restored regular biorhythmic contraction and relaxation, improving blood distribution patterns. Further-more, glycine reversed the lower amplitudes of endothelial oscillators in T1DM mice. Ultrastructural deterioration of islet microvascular endothelial cells (IMECs) and islet microvascular pericytes, including membrane and organelle damage, collagenous fiber proliferation, and reduced edema, was substantially reversed by glycine supplementation. Additionally, glycine supplementation inhibited the production of IL-6, TNF-α, IFN-γ, pro-MMP-9, and VEGF-A in T1DM, with no significant changes in energetic metabolism observed in glycine-supplemented IMECs. A statistically significant decrease in MDA levels accompanied by an increase in SOD levels was also observed with glycine supplementation. Notably, negative correlations emerged between inflammatory cytokines and microhemodynamic profiles. These findings suggest that glycine supplementation may offer a promising therapeutic approach for protecting against pancreatic microcirculatory dysfunction in T1DM.

Death-associated protein kinase 3 regulates the myogenic reactivity of cerebral arteries

NEW FINDINGS

What is the central question of this study? DAPK3 contributes to the Ca2+ -sensitization of vascular smooth muscle contraction: does this protein kinase participate in the myogenic response of cerebral arteries? What is the main finding and its importance? Small molecule inhibitors of DAPK3 effectively block the myogenic responses of cerebral arteries. HS38-dependent changes to vessel constriction occur independent of LC20 phosphorylation, and therefore DAPK3 appears to operate via the actin cytoskeleton. A role for DAPK3 in the myogenic response was not previously reported, and the results support a potential new therapeutic target in the cerebrovascular system.

ABSTRACT

The vascular smooth muscle (VSM) of resistance blood vessels is a target of intrinsic autoregulatory responses to increased intraluminal pressure, the myogenic response. In the brain, the myogenic reactivity of cerebral arteries is critical to homeostatic blood flow regulation. Here we provide the first evidence to link the death-associated protein kinase 3 (DAPK3) to the myogenic response of rat and human cerebral arteries. DAPK3 is a Ser/Thr kinase involved in Ca2+ -sensitization mechanisms of smooth muscle contraction. Ex vivo administration of a specific DAPK3 inhibitor (i.e., HS38) could attenuate vessel constrictions invoked by serotonin as well as intraluminal pressure elevation. The HS38-dependent dilatation was not associated with any change in myosin light chain (LC20) phosphorylation. The results suggest that DAPK3 does not regulate Ca2+ sensitization pathways during the myogenic response of cerebral vessels but rather operates to control the actin cytoskeleton. A slow return of myogenic tone was observed during the sustained ex vivo exposure of cerebral arteries to HS38. Recovery of tone was associated with greater LC20 phosphorylation that suggests intrinsic signalling compensation in response to attenuation of DAPK3 activity. Additional experiments with VSM cells revealed HS38- and siDAPK-dependent effects on the actin cytoskeleton and focal adhesion kinase phosphorylation status. The translational importance of DAPK3 to the human cerebral vasculature was noted, with robust expression of the protein kinase and significant HS38-dependent attenuation of myogenic reactivity found for human pial vessels.

Impact of impaired cerebral blood flow autoregulation on cognitive impairment

Although the causes of cognitive impairment are multifactorial, emerging evidence indicates that cerebrovascular dysfunction plays an essential role in dementia. One of the most critical aspects of cerebrovascular dysfunction is autoregulation of cerebral blood flow (CBF), mainly mediated by the myogenic response, which is often impaired in dementia individuals with comorbidities, such as diabetes and hypertension. However, many unsolved questions remain. How do cerebrovascular networks coordinately modulate CBF autoregulation in health and disease? Does poor CBF autoregulation have an impact on cognitive impairment, and what are the underlying mechanisms? This review summarizes the cerebral vascular structure and myogenic (a three-phase model), metabolic (O2, CO2, adenosine, and H+), and endothelial (shear stress) factors in the regulation of CBF; and the consequences of CBF dysautoregulation. Other factors contributing to cerebrovascular dysfunction, such as impaired functional hyperemia and capillary abnormalities, are included as well. Moreover, this review highlights recent studies from our lab in terms of novel mechanisms involved in CBF autoregulation and addresses a hypothesis that there is a three-line of defense for CBF autoregulation in the cerebral vasculature.

Mural Cell SRF Controls Pericyte Migration, Vessel Patterning and Blood Flow

Pericytes and vascular smooth muscle cells, collectively known as mural cells, are recruited through PDGFB (platelet-derived growth factor B)-PDGFRB (platelet-derived growth factor receptor beta) signaling. MCs are essential for vascular integrity, and their loss has been associated with numerous diseases. Most of this knowledge is based on studies in which MCs are insufficiently recruited or fully absent upon inducible ablation. In contrast, little is known about the physiological consequences that result from impairment of specific MC functions. Here, we characterize the role of the transcription factor SRF (serum response factor) in MCs and study its function in developmental and pathological contexts.

The emerging significance of circadian rhythmicity in microvascular resistance

The Earth's rotation generates environmental oscillations (e.g., in light and temperature) that have imposed unique evolutionary pressures over millions of years. Consequently, the circadian clock, a ubiquitously expressed molecular system that aligns cellular function to these environmental cues, has become an integral component of our physiology. The resulting functional rhythms optimize and economize physiological performance: perturbing these rhythms, therefore, is frequently deleterious. This perspective article focuses on circadian rhythms in resistance artery myogenic reactivity, a key mechanism governing tissue perfusion, total peripheral resistance and systemic blood pressure. Emerging evidence suggests that myogenic reactivity rhythms are locally generated in a microvascular bed-specific manner at the level of smooth muscle cells. This implies that there is a distinct interface between the molecular clock and the signalling pathways underlying myogenic reactivity in the microvascular beds of different organs. By understanding the precise nature of these molecular links, it may become possible to therapeutically manipulate microvascular tone in an organ-specific manner. This raises the prospect that interventions for vascular pathologies that are challenging to treat, such as hypertension and brain malperfusion, can be significantly improved.

Guidelines for the measurement of vascular function and structure in isolated arteries and veins

The measurement of vascular function in isolated vessels has revealed important insights into the structural, functional, and biomechanical features of the normal and diseased cardiovascular system and has provided a molecular understanding of the cells that constitutes arteries and veins and their interaction. Further, this approach has allowed the discovery of vital pharmacological treatments for cardiovascular diseases. However, the expansion of the vascular physiology field has also brought new concerns over scientific rigor and reproducibility. Therefore, it is appropriate to set guidelines for the best practices of evaluating vascular function in isolated vessels. These guidelines are a comprehensive document detailing the best practices and pitfalls for the assessment of function in large and small arteries and veins. Herein, we bring together experts in the field of vascular physiology with the purpose of developing guidelines for evaluating ex vivo vascular function. By using this document, vascular physiologists will have consistency among methodological approaches, producing more reliable and reproducible results.

Transient receptor potential channel-dependent myogenic responsiveness in small-sized resistance arteries

It is well documented that the inherent ability of small arteries and arterioles to regulate intraluminal diameter in response to alterations in intravascular pressure determines peripheral vascular resistance and blood flow (termed myogenic response or pressure-induced vasoconstriction/dilation). This autoregulatory property of resistance arteries is primarily originated from mechanosensitive vascular smooth muscle cells (VSMCs). There are diverse biological apparatuses in the plasma membrane of VSMCs that sense mechanical stimuli and generate intracellular signals for the contractility of VSMCs. Although the roles of transient receptor potential (TRP) channels in pressure-induced vasoconstriction are not fully understood to date, TRP channels that are directly activated by mechanical stimuli (e.g., stretch of VSMCs) or indirectly evoked by intracellular molecules (e.g., inositol trisphosphate) provide the major sources of Ca²⁺ (e.g., Ca²⁺ influx or release from the sarcoplasmic reticulum) and in turn, evoke vascular reactivity. This review sought to summarize mounting evidence over several decades that the activation of TRP canonical, TRP melastatin, TRP vanilloid, and TRP polycystin channels contributes to myogenic vasoconstriction.

Simulating Dynamics of Circulation in the Awake State and Different Stages of Sleep Using Non-autonomous Mathematical Model With Time Delay

We propose a mathematical model of the human cardiovascular system. The model allows one to simulate the main heart rate, its variability under the influence of the autonomic nervous system, breathing process, and oscillations of blood pressure. For the first time, the model takes into account the activity of the cerebral cortex structures that modulate the autonomic control loops of blood circulation in the awake state and in various stages of sleep. The adequacy of the model is demonstrated by comparing its time series with experimental records of healthy subjects in the SIESTA database. The proposed model can become a useful tool for studying the characteristics of the cardiovascular system dynamics during sleep.