Maurice H. Laughlin

Individuals with heart failure (HF) frequently present with comorbidities, including obesity, insulin resistance, hypertension, and dyslipidemia. Many patients with HF experience cardiogenic dementia, yet the pathophysiology of this disease remains poorly understood. Using a swine model of cardiometabolic HF (Western diet+aortic banding; WD-AB), we tested the hypothesis that WD-AB would promote a multidementia phenotype involving cerebrovascular dysfunction alongside evidence of Alzheimer’s disease (AD) pathology. The results provide evidence of cerebrovascular insufficiency coupled with neuroinflammation and amyloidosis in swine with experimental cardiometabolic HF. Although cardiac ejection fraction was normal, indices of arterial compliance and cerebral blood flow were reduced, and cerebrovascular regulation was impaired in the WD-AB group. Cerebrovascular dysfunction occurred concomitantly with increased MAPK signaling and amyloidogenic processing (i.e., increased APP, BACE1, CTF, and Aβ40 in the prefrontal cortex and hippocampus) in the WD-AB group. Transcriptomic profiles of the stellate ganglia revealed the WD-AB group displayed an enrichment of gene networks associated with MAPK/ERK signaling, AD, frontotemporal dementia, and a number of behavioral phenotypes implicated in cognitive impairment. These provide potentially novel evidence from a swine model that cerebrovascular and neuronal pathologies likely both contribute to the dementia profile in a setting of cardiometabolic HF.

We present the hypothesis that exercise-induced hyperemia, perhaps through vascular shear stress, represents an important factor responsible for the effects of physical activity (PA) on vascular insulin sensitivity. Specifically, we postulate PA involving the greatest amount of skeletal muscle mass and the greatest central neural recruitment maximizes perfusion and consequently enhances vascular insulin sensitivity in the skeletal muscle and brain.

EXT‐induced arteriolar adaptations in skeletal muscle are heterogeneous because of spatial variations in muscle fiber type composition and fiber recruitment patterns during exercise. The purpose of this report is to summarize a series of experiments conducted to test the hypothesis that changes in vascular gene expression are signaled by alterations in shear stress resulting from increases in blood flow, muscle fiber type composition, and fiber recruitment patterns. We also report results from a follow‐up study of Ankrd23, one gene whose expression was changed by EXT. We expected to see differences in magnitude of changes in gene expression along arteriolar trees and between/among arteriolar trees but similar directional changes. However, transcriptional profiles of arterioles/arteries from OLETF rats exposed to END or SIT reveal that EXT does not lead to similar directional changes in the transcriptome among arteriolar trees of different skeletal muscles or along arteriolar trees within a particular muscle. END caused the most changes in gene expression in 2A arterioles of soleus and white gastrocnemius with little to no changes in the FAs. Ingenuity Pathway Analysis across vessels revealed significant changes in gene expression in 18 pathways. EXT increased expression of some genes (Shc1, desert hedgehog protein (Dhh), adenylate cyclase 4 (Adcy4), G protein‐binding protein, alpha (Gnat1), and Bcl2l1) in all arterioles examined, but decreased expression of ubiquitin D (Ubd) and cAMP response element modulator (Crem). Many contractile and/or structural protein genes were increased by SIT in the gastrocnemius FA, but the same genes exhibited decreased expression in red gastrocnemius arterioles. Ankrd23 mRNA levels increased with increasing branch order in the gastrocnemius arteriolar tree and were increased 19‐fold in gastrocnemius muscle FA by SIT. Follow‐up experiments indicate that Ankrd23 mRNA level was increased 14‐fold in cannulated gastrocnemius FA when intraluminal pressure was increased from 90 and 180 cm H2O for 4 hours. Also, Ankrd23^−/− mice exhibit limited ability to form collateral arteries following femoral artery occlusion compared to WT mice (angioscore WT=0.18±0.03; Ankrd23^−/−=0.04±0.01). Further research will be required to determine whether Ankrd23 plays an important role in mechanically induced vascular remodeling of the arterial tree in skeletal muscle.

This manuscript summarizes and discusses adaptations of skeletal muscle vasculature induced by physical activity and applies this understanding to benefits of exercise in prevention and treatment of type 2 diabetes (T2D). Arteriolar trees of skeletal muscle are heterogeneous. Exercise training increases capillary exchange and blood flow capacities. The distribution of vascular adaptation to different types of exercise training are influenced by muscle fiber type composition and fiber recruitment patterns that produce different modes of exercise. Thus training-induced adaptations in vascular structure and vascular control in skeletal muscle are not homogeneously distributed throughout skeletal muscle or along the arteriolar tree within a muscle. Results summarized indicate that similar principles apply to vascular adaptation in skeletal muscle in T2D. It is concluded that exercise training-induced changes in vascular gene expression differ along the arteriolar tree and by skeletal muscle fiber type composition. Results suggest that it is unlikely that hemodynamic forces are the only exercise-induced signals mediating the regulation of vascular gene expression. In patients with T2D, exercise training is perhaps the most effective treatment of the many related symptoms. Training-induced changes in the vasculature and in insulin signaling in the muscle fibers and vasculature augment glucose and insulin delivery as well as glucose uptake. If these adaptations occur in a sufficient amount of muscle mass, exposure to hyperglycemia and hyperinsulinemia will decrease along with the risk of microvascular complications throughout the body. It is postulated that exercise sessions in programs of sufficient duration, that engage as much skeletal muscle mass as possible, and that recruit as many muscle fibers within each muscle as possible will produce the greatest benefit. The added benefit of combined resistance and aerobic training programs and of high-intensity exercise programs is not simply “more exercise is better”.

Using next-generation, transcriptome-wide RNA sequencing (RNA-Seq) technology we assessed the effects of exercise training on transcriptional profiles in skeletal muscle arterioles isolated from the soleus and gastrocnemius muscles of Otsuka Long Evans Tokushima Fatty (OLETF) rats that underwent an endurance exercise training program (EX; n = 13), interval sprint training program (SPRINT; n = 14), or remained sedentary (Sed; n = 12). We hypothesized that the greatest effects of exercise would be in the gastrocnemius arterioles. Results show that EX caused the largest number of changes in gene expression in the soleus and white gastrocnemius 2a arterioles with little to no changes in the feed arteries. In contrast, SPRINT caused substantial changes in gene expression in the feed arteries. IPA canonical pathway analysis revealed 18 pathways with significant changes in gene expression when analyzed across vessels and revealed that EX induces increased expression of the following genes in all arterioles examined: Shc1, desert hedgehog protein (Dhh), adenylate cyclase 4 (Adcy4), G protein binding protein, alpha (Gnat1), and Bcl2l1 and decreased expression of ubiquitin D (Ubd) and cAMP response element modulator (Crem). EX increased expression of endothelin converting enzyme (Ece1), Hsp90b, Fkbp5, and Cdcl4b in four of five arterioles. SPRINT had effects on expression of Crem, Dhh, Bcl2l1, and Ubd that were similar to EX. SPRINT also increased expression of Nfkbia, Hspa5, Tubb 2a and Tubb 2b, and Fkbp5 in all five arterioles and increased expression of Gnat1 in all but the soleus second-order arterioles. Many contractile and/or structural protein genes were increased by SPRINT in the gastrocnemius feed artery, but the same genes exhibited decreased expression in red gastrocnemius arterioles. We conclude that training-induced changes in arteriolar gene expression patterns differ by muscle fiber type composition and along the arteriolar tree.

We employed next-generation, transcriptome-wide RNA sequencing (RNA-Seq) technology to assess the effects of two different exercise training protocols on transcriptional profiles in diaphragm second-order arterioles (D2a) and in the diaphragm feed artery (DFA) from Otsuka Long Evans Tokushima Fatty (OLETF) rats. Arterioles were isolated from the diaphragm of OLETF rats that underwent an endurance exercise training program (EX; n = 13), interval sprint training program (SPRINT; n = 14), or remained sedentary (Sed; n = 12). Our hypothesis was that exercise training would have similar effects on gene expression in the diaphragm and soleus muscle arterioles because diaphragm blood flow increases during exercise to a similar extent as in soleus. Results reveal that several canonical pathways that were significantly altered by exercise in limb skeletal muscles were not among the pathways significantly changed in the diaphragm arterioles including actin cytoskeleton signaling, role of NFAT in regulation of immune response, protein kinase A signaling, and protein ubiquitination pathway. EX training altered the expression of a smaller number of genes than did SPRINT in the DFA but induced a larger number of genes with altered expression in the D2a than did SPRINT. In fact, FDR differential expression analysis (FDR, 10%) indicated that only two genes exhibited altered expression in D2a of SPRINT rats. Very few of the genes that exhibited altered expression in the DFA or D2a were also altered in limb muscle arterioles. Finally, results indicate that the 2a arterioles of soleus muscle (S2a) from endurance-trained animals and the DFA of SPRINT animals exhibited the largest number of genes with altered expression.

Background: In humans there is a positive association between epicardial adipose tissue (EAT) volume and coronary atherosclerosis (CAD) burden. We tested the hypothesis that EAT contributes locally to CAD in a pig model. Methods: Ossabaw miniature swine (n = 9) were fed an atherogenic diet for 6 months to produce CAD. A 15 mm length by 3–5 mm width coronary EAT (cEAT) resection was performed over the middle segment of the left anterior descending artery (LAD) 15 mm distal to the left main bifurcation. Pigs recovered for 3 months on atherogenic diet. Intravascular ultrasound (IVUS) was performed in the LAD to quantify atheroma immediately after adipectomy and was repeated after recovery before sacrifice. Coronary wall biopsies were stained immunohistochemically for atherosclerosis markers and cytokines and cEAT was assayed for atherosclerosis-related genes by RT-PCR. Total EAT volume was measured by non-contrast CT before each IVUS. Results: Circumferential plaque length increased (p < 0.05) in the proximal and distal LAD segments from baseline until sacrifice whereas plaque length in the middle LAD segment underneath the adipectomy site did not increase. T-cadherin, scavenger receptor A and adiponectin were reduced in the intramural middle LAD. Relative to control pigs without CAD, 11β-hydroxysteroid dehydrogenase (11βHSD-1), CCL19, CCL21, prostaglandin D₂ synthase, gp91phox [NADPH oxidase], VEGF, VEGFGR1, and angiotensinogen mRNAs were up-regulated in cEAT. EAT volume increased over 3 months. Conclusion: In pigs used as their own controls, resection of cEAT decreased the progression of CAD, suggesting that cEAT may exacerbate coronary atherosclerosis.

Hypercholesterolemia impairs endothelial function [e.g., the nitric oxide (NO)-cyclic GMP-phosphodiesterase 5 (PDE5) pathway], limits shear stress-induced vasodilation, and is therefore expected to reduce exercise-induced vasodilation. To assess the actual effects of hypercholesterolemia on endothelial function and exercise-induced vasodilation, we compared the effects of endothelial NO synthase (eNOS) and PDE5 inhibition in chronically instrumented Yucatan (Control) and Rapacz familial hypercholesterolemic (FH) swine, at rest and during treadmill exercise. The increases in systemic vascular conductance produced by ATP (relative to nitroprusside) and exercise were blunted in FH compared with Control swine. The vasoconstrictor response to eNOS inhibition, with nitro-l-arginine (NLA), was attenuated in FH compared with Control swine, both at rest and during exercise. Furthermore, whereas the vasodilator response to nitroprusside was enhanced slightly, the vasodilator response to PDE5 inhibition, with EMD360527, was reduced in FH compared with Control swine. Finally, in the pulmonary circulation, FH resulted in attenuated vasodilator responses to ATP, while maintaining the responses to both NLA and EMD360527. In conclusion, hypercholesterolemia reduces exercise-induced vasodilation in the systemic but not the pulmonary circulation. This reduction appears to be the principal result of a decrease in NO bioavailability, which is mitigated by a lower PDE5 activity.