Autophagy in vascular disease.

Autophagy is a reparative, life-sustaining process by which cytoplasmic components are sequestered in double-membrane vesicles and degraded on fusion with lysosomal compartments. Growing evidence reveals that basal autophagy is an essential in vivo process mediating proper vascular function. Moreover, autophagy is stimulated by many stress-related stimuli in the arterial wall to protect endothelial cells and smooth muscle cells against cell death and the initiation of vascular disease, in particular atherosclerosis. Basal autophagy is atheroprotective during early atherosclerosis but becomes dysfunctional in advanced atherosclerotic plaques. Little is known about autophagy in other vascular disorders, such as aneurysm formation, arterial aging, vascular stiffness, and chronic venous disease, even though autophagy is often impaired. This finding highlights the need for pharmacological interventions with compounds that stimulate the prosurvival effects of autophagy in the vasculature. A large number of animal studies and clinical trials have indicated that oral or stent-based delivery of the autophagy inducer rapamycin or derivatives thereof, collectively known as rapalogs, effectively inhibit the basic mechanisms that control growth and destabilization of atherosclerotic plaques. Other autophagy-inducing drugs, such as spermidine or add-on therapy with widely used antiatherogenic compounds, including statins and metformin, are potentially useful to prevent vascular disease with minimal adverse effects.

Defective autophagy in vascular smooth muscle cells alters contractility and Ca²âº homeostasis in mice.

Autophagy is an evolutionary preserved process that prevents the accumulation of unwanted cytosolic material through the formation of autophagosomes. Although autophagy has been extensively studied to understand its function in normal physiology, the role of vascular smooth muscle (SM) cell (VSMC) autophagy in Ca(2+) mobilization and contraction remains poorly understood. Recent evidence shows that autophagy is involved in controlling contractile function and Ca(2+) homeostasis in certain cell types. Therefore, autophagy might also regulate contractile capacity and Ca(2+)-mobilizing pathways in VSMCs. Contractility (organ chambers) and Ca(2+) homeostasis (myograph) were investigated in aortic segments of 3.5-mo-old mice containing a SM cell-specific deletion of autophagy-related 7 (Atg7; Atg7(fl/fl) SM22α-Cre(+) mice) and in segments of corresponding control mice (Atg7(+/+) SM22α-Cre(+)). Our results indicate that voltage-gated Ca(2+) channels (VGCCs) of Atg7(fl/fl) SM22α-Cre(+) VSMCs were more sensitive to depolarization, independent of changes in resting membrane potential. Contractions elicited with K(+) (50 mM) or the VGCC agonist BAY K8644 (100 nM) were significantly higher due to increased VGCC expression and activity. Interestingly, the sarcoplasmic reticulum of Atg7(fl/fl) SM22α-Cre(+) VSMCs was enlarged, which, combined with increased sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 expression and higher store-operated Ca(2+) entry, promoted inositol 1,4,5-trisphosphate-mediated contractions of Atg7(fl/fl) SM22α-Cre(+) segments and maximized the Ca(2+) storing capacity of the sarcoplasmic reticulum. Moreover, decreased plasma membrane Ca(2+)-ATPase expression in Atg7(fl/fl) SM22α-Cre(+) VSMCs hampered Ca(2+) extrusion to the extracellular environment. Overall, our study indicates that defective autophagy in VSMCs leads to an imbalance between Ca(2+) release/influx and Ca(2+) reuptake/extrusion, resulting in higher basal Ca(2+) concentrations and significant effects on vascular reactivity.

Spermidine reduces lipid accumulation and necrotic core formation in atherosclerotic plaques via induction of autophagy.

BACKGROUND AND AIMS: Spermidine is an endogenous biological polyamine that exhibits broad longevity-extending activities via the induction of autophagy. Because basal autophagy is atheroprotective during early atherosclerosis but dysfunctional in advanced plaques, the aim of the present study was to assess the potential beneficial effects of autophagy induction by spermidine on atherosclerotic plaque progression and composition. METHODS: Apolipoprotein E-deficient (ApoE(-/-)) mice were fed a Western-type diet for 20 weeks with or without 5 mM spermidine in the drinking water. RESULTS: (Immuno-)histochemical analysis of plaques in the aortic root, proximal ascending aorta and brachiocephalic artery showed that spermidine changed neither the size of the plaque nor its cellular composition. However, spermidine treatment significantly reduced necrotic core formation (6.6 ± 0.5% vs. 3.7 ± 0.5% in aortic root, p = 0.0008) and lipid accumulation inside the plaque (27 ± 3% vs. 17 ± 1% oil red O positivity in thoracic aorta, p = 0.017). In vitro experiments showed that macrophages, unlike vascular smooth muscle cells (VSMCs), were relatively insensitive to autophagy induction by spermidine. Along these lines, spermidine triggered cholesterol efflux in autophagy-competent VSMCs (5.7 ± 1.2% vs. 8.7 ± 0.2%, p = 0.0118), but not in autophagy-deficient Atg7(F/F)SM22α-Cre(+) VSMCs or macrophages. Analogous to the experiments in vitro, spermidine affected neither necrosis nor lipid load in plaques of Atg7(F/F)SM22α-Cre(+)ApoE(-/-) mice. CONCLUSIONS: Spermidine inhibits lipid accumulation and necrotic core formation through stimulation of cholesterol efflux, albeit without changing plaque size or cellular composition. These effects, which are driven by autophagy in VSMCs, support the general idea that autophagy induction is potentially useful to prevent vascular disease.

L-type Ca2+ channel blockers inhibit the window contraction of mouse aorta segments with high affinity.

L-type calcium channel blockers (LCCBs) reduce blood pressure more effectively in hypertensive than in normotensive subjects and are more effective in vascular smooth muscle (VSM) than in cardiac muscle. This has been explained by the depolarized resting potential of VSM in comparison with heart muscle cells and during hypertension, because both favor the "high affinity" inactivated state of the L-type calcium channel (LCC). Depolarized resting potentials, however, also increase Ca(2+) influx via window, non-inactivating LCC. The present study investigated whether these channels can be effectively blocked by nifedipine, verapamil or diltiazem, as representatives of different LCCB classes. C57Bl6 mouse aortic segments were depolarized by 50mM K(+) to attain similar degree of inactivation. The depolarization evoked biphasic contractions with the slow force component displaying higher sensitivity to LCCBs than the fast component. Removal of the fast force component increased, whereas stimulation of Ca(2+) influx with the dihydropyridine BAY K8644, a structural analog of nifedipine, decreased the efficacy of the LCCBs. Addition of LCCBs during the contraction caused concentration-dependent relaxation, which was independent of the presence of a fast force component, but still showed lower sensitivity in the presence of BAY K8644. Our data suggest that steady-state contractions by depolarization with 50mM K(+) are completely due to window Ca(2+) influx, which is preferentially inhibited by LCCBs. Furthermore, results point to interactions between the LCCB receptors and Ca(2+) ions or BAY K8644. The high affinity for open, non-inactivating LCC may play a dominant role in the anti-hypertensive effects of LCCBs.