Overview – Vascular biology in disease

The main aim of our research is to understand the physiology of blood vessels and their role in disease towards the development of therapeutic strategies to target the vascular compartment. Blood vessels are critical components of every organ, they maintain tissue homeostasis by ensuring: (i) transport of gases, nutrients, waste products and circulating cells, (ii) blood coagulation, and (iii) vascular tone and barrier. The endothelium lines the lumen of blood vessels and regulates the dynamic passage of materials and cells, whereas mural cells adhere to the abluminal surface of the endothelium and regulate vessel growth, permability and function. Both excessive and insufficient vascular network is deleterious for organisms and lead to a broad spectrum of pathogenesis. Specifically, our laboratory has strong interest in i) the fundamental understanding of physiological vessel growth and function, and ii) understanding the pathological contexts in which the vasculature plays a critical role either intrinsically, as happens in vascular anomalies, or extrinsically in cancer, as a key component of the stromal compartment, and in obesity, where the vasculature has a main role in the regulation of systemic metabolism. For our research, our lab develops unique animal models including zebrafish and mice, established cell lines, and patient-derived samples. We apply a holistic approach utilising state-of-the-art techniques as high-throughput analysis, next-generation sequencing, single cell RNA sequencing, phospho/proteomics, and high-resolution imaging. Our lab closely collaborates with clinicians to translate our research into the clinic at both the diagnostic and therapeutic levels.

Developmental and physiological vessel growth and function

Tissue growth and homoeostasis require the establishment of a functional hierarchical tubular network of blood vessels. Blood vessels are mainly formed by a process known as sprouting angiogenesis in which new vascular sprouts arise from parental vessels, grow, and fuse to an adjacent sprout or a pre-existing vessel. Our lab has discovered that endothelial cells rely on the PI3K (phosphatidylinositol 3-kinase) signalling to make blood vessels, and selectively use the PI3Ka isoform of PI3Ks during vessel growth. In addition, we have also understood how PI3K signalling regulates this developmental process. Angiogenesis is a dynamic process relying on endothelial cell rearrangements within vascular tubes, we discovered that PI3Kα regulates endothelial cell rearrangements by preventing NUAK1-dependent phosphorylation of the myosin phosphatase targeting-1 (MYPT1) protein, thereby allowing myosin light chain phosphatase (MLCP) activity and ultimately downregulating actomyosin contractility. Our findings have defined the PI3K/NUAK1/MYPT1/MLCP axis as a critical pathway to regulate actomyosin contractility in endothelial cells, supporting vascular patterning and expansion through the control of cell rearrangement. Also, vessel sprouting relies on the induction of specialized endothelial cell populations: at the very front of the sprouts, tip cells provide guidance and migrate towards gradients of vascular endothelial growth factor (VEGF)-A, but rarely proliferate; trailing stalk cells located at the base of the sprout proliferate, establish adherent and tight junctions and form the vascular lumen. Our lab discovered that PTEN (a negative regulator of PI3K signalling) is crucial for blocking stalk cell proliferation and this is critical for vessel development. We show that both the catalytic and non-catalytic APC/C-Fzr1/Cdh1-mediated activities of PTEN are required for stalk cells’ proliferative arrest. These findings define a Notch-PTEN signalling axis as an orchestrator of vessel density and implicate the PTEN-APC/C-Fzr1/Cdh1 hub in angiogenesis.

• Graupera M, et al. Angiogenesis selectively requires the p110alpha isoform of PI3K to control endothelial cell migration. Nature. 2008. May 29;453(7195):662.
• Serra H, et al. PTEN mediates Notch-dependent stalk cell arrest in angiogenesis. Nat Commun. 2015 Jul 31;6:7935.
• Angulo-Urarte A, et al. Endothelial cell rearrangement during vascular patterning requires PI3-kinase mediated suppression of actomyosin contractility. 2018. Nature Commun. Nov 16;9(1): 482.

Understanding the pathogenesis of vascular malformations

Vascular anomalies are a heterogeneous group of rare diseases affecting mainly paediatric patients for whom limited treatment options exist. Vascular malformations have a major impact on the quality of life of patients; they are painful and disfiguring, and many lead to bleeding, recurrent infections, thrombosis and organ dysfunction. These lesions are usually manifested at birth (congenital), they appear during embryonic development as a result of an abnormal vascular growth due to genetic mutations. Our lab was the first to discover that venous malformations, the most common type of vascular malformations, are caused by oncogenic mutations in the PIK3CA catalytic isoform of PI3Ks. Likewise, we were the first lab to create a genetic mouse model of venous malformations that has been key to understand the pathogenesis of venous malformations as well as a unique platform to develop targeted therapies for the disease. Hereditary haemorrhagic telangiectasia (HHT) is a rare germline disease caused by the genetic inactivation of the TGFb/BMP signalling pathway and it is characterized by the local overgrowth of the vascular plexus caused by the direct connection of arteries and veins that generate a fragile site that can easily rupture and bleed. These lesions may lead to haemorrhagic episodes in the skin, lung, liver and the digestive tract. Our lab discovered that TGFb/BMP signalling mediates vascular quiescence by limiting PI3K signalling and demonstrated that PI3K inhibitors could be used as novel therapeutic agents to treat HHT.

• Castillo SD, et al. PIK3CA mutations in vascular malformations. Curr Opin Hematol. 2019 Mar 6.
• Castillo SD, et al. Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans. Sci Transl Med. 2016 Mar 30;8(332):332ra43.
• Alsina-Sanchís E, et al. ALK1 Loss Results in Vascular Hyperplasia in Mice and Humans Through PI3K Activation. Arterioscler Thromb Vasc Biol. 2018 May;38(5):1216-1229.

Tumour angiogenesis

Tumours need blood vessels for their growth, thus providing the rationale for antiangiogenic therapy in cancer treatment. However, intrinsic and acquired resistance and low response rates have turned out to be major limitations of antiangiogenic therapy. This has emphasized the need to further understand how the vasculature in cancer can be targeted. PI3Kα is frequently mutated in cancer and this has provided the rationale to inhibit this pathway in patients. Given that endothelial cells are exquisitely regulated by PI3K signalling, our lab has been exploring whether PI3K inhibitors also interfere with the tumoral stroma compartment. Our lab has identified that tumour vessels rely on PI3K signalling to expand and has provided the rationale for specifically target the PI3Ka isoform in neuroendocrine tumours. Also, we have showed that the metabolic patterning in neuroendocrine tumours is regulated by the mTOR pathway. We are now exploring the impact of vessel normalization by PI3K signalling modulation as a therapeutic strategy for the improvement of drug delivery and immune cell access to the tumour.

• Soler A, et al. Inhibition of the p110α isoform of PI 3-kinase stimulates nonfunctional tumor angiogenesis. J Exp Med. 2013 Sep 23;210(10):1937-45.
• Soler A, et al. PI3K at the crossroads of tumor angiogenesis signaling pathways. Mol Cell Oncol. 2015 Feb 26;2(2):e975624.
• Soler A, et al. Therapeutic benefit of restricted p110a inhibition of PI3-kinase isoform in pancreatic neuroendocrine tumors. Clin Cancer Res. 2016 Dec 1;22(23):5805-5817.
• Okkenhaug K, et al. Targeting PI3K in Cancer: Impact on Tumor Cells, Their Protective Stroma, Angiogenesis, and Immunotherapy. Cancer Discov. 2016 Oct;6(10):1090-1105. Invited review.

The endothelium: a metabolic gatekeeper

Energy and metabolic homeostasis are fundamental processes to sustain life. Higher organisms have developed mechanisms to allow adequate sensing and integration of cues informing about energy status. The vascular system, which is lined up by endothelial cells, modulates nutrient distribution and availability and is thus considered the metabolic gatekeeper of the organism. Energy excess results in obesity, which is accompanied by endothelial cell dysfunction. The current paradigm states that endothelial cell dysfunction is a consequence of metabolic alterations associated with obesity. The research in our lab challenges this paradigm and proposes that endothelial cell dysfunction is indeed also causally associated to a direct cause of aberrant energy balance and metabolism. We aim to decipher the specific molecular programs altered on endothelial cells that contribute to the development of obesity and metabolic disorders.

• Graupera M and Claret M. Endothelial Cells: New Players in Obesity and Related Metabolic Disorders. Trends Endocrinol Metab. 2018 Nov;29(11):781-794.