Senescent murine femoral arteries undergo vascular remodelling associated with accelerated stress-induced contractility and reactivity to nitric oxide

SIRT-associated attenuation of cellular senescence in vascular wall

This review focuses on the vital function that SIRT1 and other sirtuins play in promoting cellular senescence in vascular smooth muscle cells, which is a key element in the pathogenesis of vascular aging and associated cardiovascular diseases. Vascular aging is a gradual process caused by the accumulation of senescent cells, which results in increased vascular remodeling, stiffness, and diminished angiogenic ability. Such physiological alterations are characterized by a complex interplay of environmental and genetic variables, including oxidative stress and telomere attrition, which affect gene expression patterns and trigger cell growth arrest. SIRT1 has been highlighted for its potential to reduce cellular senescence through modulation of multiple signaling cascades, particularly the endothelial nitric oxide (eNOS)/NO signaling pathway. It also modulates cell cycle through p53 inactivation and suppresses NF-κB mediated expression of adhesive molecules at the vascular level. The study also examines the therapeutic potential of sirtuin modulation in vascular health, identifying SIRT1 and its sirtuin counterparts as potential targets for reducing vascular aging. This study sheds light on the molecular basis of vascular aging and the beneficial effects of sirtuins, paving the way for the development of tailored therapies aimed at enhancing vascular health and prolonging life.

Aging related decreases in NM myosin expression and contractility in a resistance vessel

Introduction: Vasodilatation in response to NO is a fundamental response of the vasculature, and during aging, the vasculature is characterized by an increase in stiffness and decrease in sensitivity to NO mediated vasodilatation. Vascular tone is regulated by the activation of smooth muscle and nonmuscle (NM) myosin, which are regulated by the activities of myosin light chain kinase (MLCK) and MLC phosphatase. MLC phosphatase is a trimeric enzyme with a catalytic subunit, myosin targeting subunit (MYPT1) and 20 kDa subunit of unknown function. Alternative mRNA splicing produces LZ+/LZ- MYPT1 isoforms and the relative expression of LZ+/LZ- MYPT1 determines the sensitivity to NO mediated vasodilatation. This study tested the hypothesis that aging is associated with changes in LZ+ MYPT1 and NM myosin expression, which alter vascular reactivity. Methods: We determined MYPT1 and NM myosin expression, force and the sensitivity of both endothelial dependent and endothelial independent relaxation in tertiary mesenteric arteries of young (6mo) and elderly (24mo) Fischer344 rats. Results: The data demonstrate that aging is associated with a decrease in both the expression of NM myosin and force, but LZ+ MYPT expression and the sensitivity to both endothelial dependent and independent vasodilatation did not change. Further, smooth muscle cell hypertrophy increases the thickness of the medial layer of smooth muscle with aging. Discussion: The reduction of NM myosin may represent an aging associated compensatory mechanism to normalize the stiffness of resistance vessels in response to the increase in media thickness observed during aging.

ROK and RSK2-kinase pathways differ between senescent human renal and mesenteric arteries

OBJECTIVE

Small arteries from different organs vary with regard to the mechanisms that regulate vasoconstriction. This study investigated the impact of advanced age on the regulation of vasoconstriction in isolated human small arteries from kidney cortex and periintestinal mesenteric tissue.

METHODS

Renal and mesenteric tissues were obtained from patients (mean age 71 ± 9 years) undergoing elective surgery. Furthermore, intrarenal and mesenteric arteries from young and aged mice were studied. Arteries were investigated by small vessel myography and western blot.

RESULTS

Human intrarenal arteries (h-RA) showed higher stretch-induced tone and higher reactivity to α 1 adrenergic receptor stimulation than human mesenteric arteries (h-MA). Rho-kinase (ROK) inhibition resulted in a greater decrease in Ca 2+ and depolarization-induced tone in h-RA than in h-MA. Basal and α 1 adrenergic receptor stimulation-induced phosphorylation of the regulatory light chain of myosin (MLC 20 ) was higher in h-RA than in h-MA. This was associated with higher ROK-dependent phosphorylation of the regulatory subunit of myosin light-chain-phosphatase (MLCP), MYPT1-T853. In h-RA phosphorylation of ribosomal S6-kinase II (RSK2-S227) was significantly higher than in h-MA. Stretch-induced tone and RSK2 phosphorylation was also higher in interlobar arteries (m-IAs) from aged mice than in respective vessels from young mice and in murine mesenteric arteries (m-MA) from both age groups.

CONCLUSION

Vasoconstriction in human intrarenal arteries shows a greater ROK-dependence than in mesenteric arteries. Activation of RSK2 may contribute to intrarenal artery tone dysregulation associated with aging. Compared with h-RA, h-MA undergo age-related remodeling leading to a reduction of the contractile response to α 1 adrenergic stimulation.

Tissue-specific expression of myosin phosphatase subunits and isoforms in smooth muscle of mice and humans

Alternative splicing of exon24 (E24) of myosin phosphatase targeting subunit 1 (Mypt1) by setting sensitivity to nitric oxide (NO)/cGMP-mediated relaxation is a key determinant of smooth muscle function. Here we defined expression of myosin phosphatase (MP) subunits and isoforms by creation of new genetic mouse models, assay of human and mouse tissues, and query of public databases. A Mypt1-LacZ reporter mouse revealed that Mypt1 transcription is turned on early in development during smooth muscle differentiation. Mypt1 is not as tightly restricted in its expression as smooth muscle myosin heavy chain (Myh11) and its E6 splice variant. Mypt1 is enriched in mature smooth versus nonmuscle cells. The E24 splice variant and leucine zipper minus protein isoform that it encodes is enriched in phasic versus tonic smooth muscle. In the vascular system, E24 splicing increases as vessel size decreases. In the gastrointestinal system, E24 splicing is most predominant in smooth muscle of the small intestine. Tissue-specific expression of MP subunits and Mypt1 E24 splicing is conserved in humans, whereas a splice variant of the inhibitory subunit (CPI-17) is unique to humans. A Mypt1 E24 mini-gene splicing reporter mouse generated to define patterns of E24 splicing in smooth muscle cells (SMCs) dispersed throughout the organ systems was unsuccessful. In summary, expression of Mypt1 and splicing of E24 is part of the program of smooth muscle differentiation, is further enhanced in phasic smooth muscle, and is conserved in humans. Its low-level expression in nonmuscle cells may confound its measurement in tissue samples.