Impaired training-induced angiogenesis process with loss of pericyte-endothelium interactions is associated with an abnormal capillary remodelling in the skeletal muscle of COPD patients

Elevated Blood Pressure Occurs without Endothelial Dysfunction in a Rat Model of Pulmonary Emphysema

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung disease involving airway closure and parenchyma destruction (emphysema). Cardiovascular diseases are the main causes of morbi-mortality in COPD and, in particular, hypertension and heart failure with preserved ejection fraction (HFpEF). However, no mechanistic link has currently been established between the onset of COPD, elevated blood pressure (BP) and systemic vascular impairment (endothelial dysfunction). Thus, we aimed to characterize BP and vascular function and remodeling in a rat model of exacerbated emphysema focusing on the role of sympathetic hyperactivity. Emphysema was induced in male Wistar rats by four weekly pulmonary instillations of elastase (4UI) and exacerbation by a single dose of lipopolysaccharides (LPS). Five weeks following the last instillation, in vivo and ex vivo cardiac and vascular functions were investigated. Exacerbated emphysema induced cardiac dysfunction (HFpEF) and a BP increase in this COPD model. We observed vasomotor changes and hypotrophic remodeling of the aorta without endothelial dysfunction. Indeed, changes in contractile and vasorelaxant properties, though endothelium-dependent, were pro-relaxant and NO-independent. A β1-receptor antagonist (bisoprolol) prevented HFpEF and vascular adaptations, while the effect on BP increase was partial. Endothelial dysfunction would not trigger hypertension and HFpEF in COPD. Vascular changes appeared as an adaptation to the increased BP. The preventing effect of bisoprolol revealed a pivotal role of sympathetic hyperactivation in BP elevation. The mechanistic link between HFpEF, cardiac sympathetic activation and BP deserves further studies in this exacerbated-emphysema model, as well as in COPD patients.

Pericyte Loss in Diseases

Pericytes are specialized cells located in close proximity to endothelial cells within the microvasculature. They play a crucial role in regulating blood flow, stabilizing vessel walls, and maintaining the integrity of the blood-brain barrier. The loss of pericytes has been associated with the development and progression of various diseases, such as diabetes, Alzheimer's disease, sepsis, stroke, and traumatic brain injury. This review examines the detection of pericyte loss in different diseases, explores the methods employed to assess pericyte coverage, and elucidates the potential mechanisms contributing to pericyte loss in these pathological conditions. Additionally, current therapeutic strategies targeting pericytes are discussed, along with potential future interventions aimed at preserving pericyte function and promoting disease mitigation.

Cellular interplay in skeletal muscle regeneration and wasting: insights from animal models

Skeletal muscle wasting, whether related to physiological ageing, muscle disuse or to an underlying chronic disease, is a key determinant to quality of life and mortality. However, cellular basis responsible for increased catabolism in myocytes often remains unclear. Although myocytes represent the vast majority of skeletal muscle cellular population, they are surrounded by numerous cells with various functions. Animal models, mostly rodents, can help to decipher the mechanisms behind this highly dynamic process, by allowing access to every muscle as well as time-course studies. Satellite cells (SCs) play a crucial role in muscle regeneration, within a niche also composed of fibroblasts and vascular and immune cells. Their proliferation and differentiation is altered in several models of muscle wasting such as cancer, chronic kidney disease or chronic obstructive pulmonary disease (COPD). Fibro-adipogenic progenitor cells are also responsible for functional muscle growth and repair and are associated in disease to muscle fibrosis such as in chronic kidney disease. Other cells have recently proven to have direct myogenic potential, such as pericytes. Outside their role in angiogenesis, endothelial cells and pericytes also participate to healthy muscle homoeostasis by promoting SC pool maintenance (so-called myogenesis-angiogenesis coupling). Their role in chronic diseases muscle wasting has been less studied. Immune cells are pivotal for muscle repair after injury: Macrophages undergo a transition from the M1 to the M2 state along with the transition between the inflammatory and resolutive phase of muscle repair. T regulatory lymphocytes promote and regulate this transition and are also able to activate SC proliferation and differentiation. Neural cells such as terminal Schwann cells, motor neurons and kranocytes are notably implicated in age-related sarcopenia. Last, newly identified cells in skeletal muscle, such as telocytes or interstitial tenocytes could play a role in tissular homoeostasis. We also put a special focus on cellular alterations occurring in COPD, a chronic and highly prevalent respiratory disease mainly linked to tobacco smoke exposure, where muscle wasting is strongly associated with increased mortality, and discuss the pros and cons of animal models versus human studies in this context. Finally, we discuss resident cells metabolism and present future promising leads for research, including the use of muscle organoids.

The Role of Pericytes in Regulation of Innate and Adaptive Immunity

Pericytes are perivascular multipotent cells wrapping microvascular capillaries, where they support vasculature functioning, participate in tissue regeneration, and regulate blood flow. However, recent evidence suggests that in addition to traditionally credited structural function, pericytes also manifest immune properties. In this review, we summarise recent data regarding pericytes' response to different pro-inflammatory stimuli and their involvement in innate immune responses through expression of pattern-recognition receptors. Moreover, pericytes express various adhesion molecules, thus regulating trafficking of immune cells across vessel walls. Additionally, the role of pericytes in modulation of adaptive immunity is discussed. Finally, recent reports have suggested that the interaction with cancer cells evokes immunosuppression function in pericytes, thus facilitating immune evasion and facilitating cancer proliferation and metastasis. However, such complex and multi-faceted cross-talks of pericytes with immune cells also suggest a number of potential pericyte-based therapeutic methods and techniques for cancer immunotherapy and treatment of autoimmune and auto-inflammatory disorders.

Angiogenesis, Lymphangiogenesis, and Inflammation in Chronic Obstructive Pulmonary Disease (COPD): Few Certainties and Many Outstanding Questions

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation, predominantly affecting the lung parenchyma and peripheral airways, that results in progressive and irreversible airflow obstruction. COPD development is promoted by persistent pulmonary inflammation in response to several stimuli (e.g., cigarette smoke, bacterial and viral infections, air pollution, etc.). Angiogenesis, the formation of new blood vessels, and lymphangiogenesis, the formation of new lymphatic vessels, are features of airway inflammation in COPD. There is compelling evidence that effector cells of inflammation (lung-resident macrophages and mast cells and infiltrating neutrophils, eosinophils, basophils, lymphocytes, etc.) are major sources of a vast array of angiogenic (e.g., vascular endothelial growth factor-A (VEGF-A), angiopoietins) and/or lymphangiogenic factors (VEGF-C, -D). Further, structural cells, including bronchial and alveolar epithelial cells, endothelial cells, fibroblasts/myofibroblasts, and airway smooth muscle cells, can contribute to inflammation and angiogenesis in COPD. Although there is evidence that alterations of angiogenesis and, to a lesser extent, lymphangiogenesis, are associated with COPD, there are still many unanswered questions.

Response to Electrostimulation Is Impaired in Muscle Cells from Patients with Chronic Obstructive Pulmonary Disease

Among the comorbidities associated with chronic obstructive pulmonary disease (COPD), skeletal muscle weakness and atrophy are known to affect patient survival rate. In addition to muscle deconditioning, various systemic and intrinsic factors have been implicated in COPD muscle dysfunction but an impaired COPD muscle adaptation to contraction has never been extensively studied. We submitted cultured myotubes from nine healthy subjects and nine patients with COPD to an endurance-type protocol of electrical pulse stimulation (EPS). EPS induced a decrease in the diameter, covered surface and expression of MHC1 in COPD myotubes. Although the expression of protein degradation markers was not affected, expression of the protein synthesis marker mTOR was not induced in COPD compared to healthy myotubes after EPS. The expression of the differentiation markers p16INK4a and p21 was impaired, while expression of Myf5 and MyoD tended to be affected in COPD muscle cells in response to EPS. The expression of mitochondrial biogenesis markers PGC1α and MFN2 was affected and expression of TFAM and COX1 tended to be reduced in COPD compared to healthy myotubes upon EPS. Lipid peroxidation was increased and the expression of the antioxidant enzymes SOD2 and GPx4 was affected in COPD compared to healthy myotubes in response to EPS. Thus, we provide evidence of an impaired response of COPD muscle cells to contraction, which might be involved in the muscle weakness observed in patients with COPD.

Lung Pericytes in Pulmonary Vascular Physiology and Pathophysiology

Pericytes are mesenchymal-derived mural cells localized within the basement membrane of pulmonary and systemic capillaries. Besides structural support, pericytes control vascular tone, produce extracellular matrix components, and cytokines responsible for promoting vascular homeostasis and angiogenesis. However, pericytes can also contribute to vascular pathology through the production of pro-inflammatory and pro-fibrotic cytokines, differentiation into myofibroblast-like cells, destruction of the extracellular matrix, and dissociation from the vessel wall. In the lung, pericytes are responsible for maintaining the integrity of the alveolar-capillary membrane and coordinating vascular repair in response to injury. Loss of pericyte communication with alveolar capillaries and a switch to a pro-inflammatory/pro-fibrotic phenotype are common features of lung disorders associated with vascular remodeling, inflammation, and fibrosis. In this article, we will address how to differentiate pericytes from other cells, discuss the molecular mechanisms that regulate the interactions of pericytes and endothelial cells in the pulmonary circulation, and the experimental tools currently used to study pericyte biology both in vivo and in vitro. We will also discuss evidence that links pericytes to the pathogenesis of clinically relevant lung disorders such as pulmonary hypertension, idiopathic lung fibrosis, sepsis, and SARS-COVID. Future studies dissecting the complex interactions of pericytes with other pulmonary cell populations will likely reveal critical insights into the origin of pulmonary diseases and offer opportunities to develop novel therapeutics to treat patients afflicted with these devastating disorders. © 2021 American Physiological Society. Compr Physiol 11:2227-2247, 2021.

COPD is deleterious for pericytes: implications during training-induced angiogenesis in skeletal muscle

Improvements in skeletal muscle endurance and oxygen uptake are blunted in patients with chronic obstructive pulmonary disease (COPD), possibly because of a limitation in the muscle capillary oxygen supply. Pericytes are critical for capillary blood flow adaptation during angiogenesis but may be impaired by COPD systemic effects, which are mediated by circulating factors. This study compared the pericyte coverage of muscle capillaries in response to 10 wk of exercise training in patients with COPD and sedentary healthy subjects (SHS). Fourteen patients with COPD were compared with seven matched SHS. SHS trained at moderate intensity corresponding to an individualized moderate-intensity patient with COPD trained at the same relative (%V̇o₂: COPD-RI) or absolute (mL·min^-1·kg^-1: COPD-AI) intensity as SHS. Capillary-to-fiber ratio (C/F) and NG2⁺ pericyte coverage were assessed from vastus lateralis muscle biopsies, before and after 5 and 10 wk of training. We also tested in vitro the effect of COPD and SHS serum on pericyte morphology and mesenchymal stem cell (MSC) differentiation into pericytes. SHS showed greater improvement in aerobic capacity (V̇o_2VT) than both patients with COPD-RI and patients with COPD-AI (Group × Time: P = 0.004). Despite a preserved increase in the C/F ratio, NG2⁺ pericyte coverage did not increase in patients with COPD in response to training, contrary to SHS (Group × Time: P = 0.011). Conversely to SHS serum, COPD serum altered pericyte morphology (P < 0.001) and drastically reduced MSC differentiation into pericytes (P < 0.001). Both functional capacities and pericyte coverage responses to exercise training are blunted in patients with COPD. We also provide direct evidence of the deleterious effect of COPD circulating factors on pericyte morphology and differentiation.NEW & NOTEWORTHY This work confirms the previously reported impairment in the functional response to exercise training of patients with COPD compared with SHS. Moreover, it shows for the first time that pericyte coverage of the skeletal capillaries is drastically reduced in patients with COPD compared with SHS during training-induced angiogenesis. Finally, it provides experimental evidence that circulating factors are involved in the impaired pericyte coverage of patients with COPD.

Structural Microangiopathies in Skeletal Muscle Related to Systemic Vascular Pathologies in Humans

It is unclear how microangiopathic changes in skeletal muscle vary among systemic vascular pathologies. We therefore analyzed the capillary fine structure in skeletal muscle from patients with arterial hypertension (HYPT), diabetes mellitus type 2 (T2DM) or intermittent claudication – peripheral arterial disease (IC/PAD). Tablet-based image analysis (TBIA) was carried out to largely re-evaluate 5,000 transmission electron micrographs of capillaries from 126 vastus lateralis biopsies of 75 individuals (HYPT, T2DM or IC/PAD patients as well as healthy individuals before and after endurance exercise training) used in previous morphometric studies, but assessed using stereological counting grids of different sizes. Serial block-face scanning electron microscopy (SBFSEM) of mouse skeletal muscle was used for validation of the particular fine structural events observed in human biopsies. The peri-capillary basement membrane (BM) was 38.5 and 45.5% thicker (P < 0.05) in T2DM and IC/PAD patients than in the other groups. A 17.7–39.6% lower (P < 0.05) index for intraluminal endothelial cell (EC) surface enlargement by projections was exclusively found in T2DM patients by TBIA morphometry. The proportion of capillaries with disrupted BM between pericytes (PC) and EC was higher (P < 0.05) in HYPT (33.2%) and T2DM (38.7%) patients than in the control group. Empty EC-sockets were more frequent (P < 0.05) in the three patient groups (20.6% in HYPT, 27.1% in T2DM, 30.0% in IC/PAD) than in the healthy individuals. SBFSEM confirmed that EC-sockets may exhibit close proximity to the capillary lumen. Our comparative morphometric analysis demonstrated that structural arrangement of skeletal muscle capillaries is more affected in T2DM than in HYPT or IC/PAD, although some similar elements of remodeling were found. The increased frequency of empty EC-sockets in the three patient groups indicates that the PC-EC interaction is commonly disturbed in these systemic vascular pathologies.