Phosphoinositide 3-Kinase-Regulated Pericyte Maturation Governs Vascular Remodeling.

BACKGROUND: Pericytes regulate vessel stabilization and function, and their loss is associated with diseases such as diabetic retinopathy or cancer. Despite their physiological importance, pericyte function and molecular regulation during angiogenesis remain poorly understood. METHODS: To decipher the transcriptomic programs of pericytes during angiogenesis, we crossed Pdgfrb(BAC)-CreERT2 mice into RiboTagflox/flox mice. Pericyte morphological changes were assessed in mural cell-specific R26-mTmG reporter mice, in which low doses of tamoxifen allowed labeling of single-cell pericytes at high resolution. To study the role of phosphoinositide 3-kinase (PI3K) signaling in pericyte biology during angiogenesis, we used genetic mouse models that allow selective inactivation of PI3Kα and PI3Kß isoforms and their negative regulator phosphate and tensin homolog deleted on chromosome 10 (PTEN) in mural cells. RESULTS: At the onset of angiogenesis, pericytes exhibit molecular traits of cell proliferation and activated PI3K signaling, whereas during vascular remodeling, pericytes upregulate genes involved in mature pericyte cell function, together with a remarkable decrease in PI3K signaling. Immature pericytes showed stellate shape and high proliferation, and mature pericytes were quiescent and elongated. Unexpectedly, we demonstrate that PI3Kß, but not PI3Kα, regulates pericyte proliferation and maturation during vessel formation. Genetic PI3Kß inactivation in pericytes triggered early pericyte maturation. Conversely, unleashing PI3K signaling by means of PTEN deletion delayed pericyte maturation. Pericyte maturation was necessary to undergo vessel remodeling during angiogenesis. CONCLUSIONS: Our results identify new molecular and morphological traits associated with pericyte maturation and uncover PI3Kß activity as a checkpoint to ensure appropriate vessel formation. In turn, our results may open new therapeutic opportunities to regulate angiogenesis in pathological processes through the manipulation of pericyte PI3Kß activity.

Pericytes in the disease spotlight.

Pericytes are known as the mural cells in small-caliber vessels that interact closely with the endothelium. Pericytes play a key role in vasculature formation and homeostasis, and when dysfunctional contribute to vasculature-related diseases such as diabetic retinopathy and neurodegenerative conditions. In addition, significant extravascular roles of pathological pericytes are being discovered with relevant implications for cancer and fibrosis. Pericyte research is challenged by the lack of consistent molecular markers and clear discrimination criteria versus other (mural) cells. However, advances in single-cell approaches are uncovering and clarifying mural cell identities, biological functions, and ontogeny across organs. We discuss the latest developments in pericyte pathobiology to inform future research directions and potential outcomes.

Angiocrine polyamine production regulates adiposity.

Reciprocal interactions between endothelial cells (ECs) and adipocytes are fundamental to maintain white adipose tissue (WAT) homeostasis, as illustrated by the activation of angiogenesis upon WAT expansion, a process that is impaired in obesity. However, the molecular mechanisms underlying the crosstalk between ECs and adipocytes remain poorly understood. Here, we show that local production of polyamines in ECs stimulates adipocyte lipolysis and regulates WAT homeostasis in mice. We promote enhanced cell-autonomous angiogenesis by deleting Pten in the murine endothelium. Endothelial Pten loss leads to a WAT-selective phenotype, characterized by reduced body weight and adiposity in pathophysiological conditions. This phenotype stems from enhanced fatty acid ß-oxidation in ECs concomitant with a paracrine lipolytic action on adipocytes, accounting for reduced adiposity. Combined analysis of murine models, isolated ECs and human specimens reveals that WAT lipolysis is mediated by mTORC1-dependent production of polyamines by ECs. Our results indicate that angiocrine metabolic signals are important for WAT homeostasis and organismal metabolism.

Genetic manipulation of LKB1 elicits lethal metastatic prostate cancer.

Gene dosage is a key defining factor to understand cancer pathogenesis and progression, which requires the development of experimental models that aid better deconstruction of the disease. Here, we model an aggressive form of prostate cancer and show the unconventional association of LKB1 dosage to prostate tumorigenesis. Whereas loss of Lkb1 alone in the murine prostate epithelium was inconsequential for tumorigenesis, its combination with an oncogenic insult, illustrated by Pten heterozygosity, elicited lethal metastatic prostate cancer. Despite the low frequency of LKB1 deletion in patients, this event was significantly enriched in lung metastasis. Modeling the role of LKB1 in cellular systems revealed that the residual activity retained in a reported kinase-dead form, LKB1K78I, was sufficient to hamper tumor aggressiveness and metastatic dissemination. Our data suggest that prostate cells can function normally with low activity of LKB1, whereas its complete absence influences prostate cancer pathogenesis and dissemination.

Stromal markers of activated tumor associated fibroblasts predict poor survival and are associated with necrosis in non-small cell lung cancer.

OBJECTIVES: Tumor associated fibroblasts (TAFs) are essential contributors of the progression of non-small cell lung cancer (NSCLC). Most lung TAFs exhibit an activated phenotype characterized by the expression of α-SMA and fibrillar collagens. However, the prognostic value of these activation markers in NSCLC remains unclear. MATERIAL AND METHODS: We conducted a quantitative image analysis of α-SMA immunostaining and picrosirius red staining of fibrillar collagens imaged by bright-field and polarized microscopy, respectively, using tissue microarrays with samples from 220 surgical patients, which elicited a percentage of positive staining area for each marker and patient. RESULTS: Kaplan-Meier curves showed that all TAF activation markers were significantly associated with poor survival, and their prognostic value was independent of TNM staging as revealed by multivariate analysis, which elicited an adjusted increased risk of death after 3 years of 129% and 94% for fibrillar collagens imaged with bright-field (p = 0.004) and polarized light (p = 0.003), respectively, and of 89% for α-SMA (p = 0.009). We also found a significant association between all TAF activation markers and tumor necrosis, which is often indicative of hypoxia, supporting a pathologic link between tumor desmoplasia and necrosis/hypoxia. CONCLUSIONS: Our findings identify patients with large histologic coverage of fibrillar collagens and α-SMA + TAFs to be at higher risk of recurrence and death, supporting that they could be considered for adjuvant therapy.

Tumor-associated metabolic and inflammatory responses in early stage non-small cell lung cancer: Local patterns and prognostic significance.

INTRODUCTION: Non-small cell lung cancer (NSCLC) patients diagnosed in early stage and surgically-treated have five-year mortality rate >20%. The identification of biomarkers able to predict progression and death may help to identify patients needing closer follow-up. METHODS: A retrospective cohort of early-stage surgically-treated NSCLC patients enrolled in the International Association for the Study of Lung Cancer (IASLC) Staging Project was created, and tissue Microarrays (TMAs) were constructed with tumor and non-tumor lung tissue. Pentose phosphate pathway (PPP) proteins (transketolase [TKT] and transketolase-like 1 [TKTL1]), inflammatory markers (cyclooxygenase-2 [COX-2], tumor necrosis factor alpha [TNF-α], interleukin 1 beta [IL1ß], nuclear factor kappa-light-chain-enhancer of activated B cells [NFκB]-p65 and antigen Ki-67), and programmed death-ligand 1 (PDL1) were measured by immunohistochemistry. RESULTS: NSCLC patients with adenocarcinoma (ADC) or squamous cell carcinoma (SCC) were included in the study (n = 199). TKT and TKTL1 were significantly higher in ADC than in non-tumor tissue (p < 0.001). Higher values were also observed in NSCLC for all the inflammatory markers, with figures >30% above those of non-tumor tissue (p < 0.001). PDL1 analysis showed a higher percentage of positivity in ADC than in non-tumor tissue (p < 0.001). Multivariate Cox proportional hazards modeling confirmed that high IL1ß level in tumor tissue was independently associated with 3-year mortality in NSCLC [HR = 2.05, 95% CI (1.1-3.7), p = 0.019], a relationship driven by ADC subtype. CONCLUSION: This study confirms an increase in metabolic activity and an inflammatory response in tumor tissue of early stage NSCLC, and a significant relationship between high levels of IL1ß in the tumor and poor prognosis in ADC.