Inflammation is associated with blood vessel and lymphatic vessel proliferation and remodeling. The microvasculature of the mouse trachea provides an ideal opportunity to study this process, as Mycoplasma pulmonis infection of mouse airways induces widespread and sustained vessel remodeling, including enlargement of capillaries into venules and lymphangiogenesis. Although the mediators responsible for these vascular changes in mice have not been identified, VEGF-A is known not to be involved. Here, we sought to determine whether TNF-α drives the changes in blood vessels and lymphatics in M. pulmonis-infected mice. The endothelial cells, but not pericytes, of blood vessels, but not lymphatics, were immunoreactive for TNF receptor 1 (TNF-R1) and lymphotoxin B receptors. Most TNF-R2 immunoreactivity was on leukocytes. Infection resulted in a large and sustained increase in TNF-α expression, as measured by real-time quantitative RT-PCR, and smaller increases in lymphotoxins and TNF receptors that preceded vessel remodeling. Substantially less vessel remodeling and lymphangiogenesis occurred when TNF-α signaling was inhibited by a blocking antibody or was silenced in Tnfr1 -/-mice. When administered after infection was established, the TNF-α-specific antibody slowed but did not reverse blood vessel remodeling and lymphangiogenesis. The action of TNF-α on blood vessels is probably mediated through direct effects on endothelial cells, but its effects on lymphangiogenesis may require inflammatory mediators from recruited leukocytes. We conclude that TNF-α is a strong candidate for a mediator that drives blood vessel remodeling and lymphangiogenesis in inflammation. IntroductionA wide spectrum of changes in blood vessels occurs in inflammation. Acute inflammation is accompanied by reversible vasodilatation, increased blood flow, plasma extravasation, and leukocyte adhesion and transmigration. In chronic inflammation, characteristic of asthma, obstructive pulmonary disease, rheumatoid arthritis, psoriasis, and inflammatory bowel disease, blood vessels and lymphatic vessels proliferate and undergo remodeling with changes in structural, functional, and molecular phenotypes. As part of the remodeling, capillaries enlarge and transform into venules that contribute to leukocyte adhesion and migration unpublished observations). Lymphatic vessels not only sprout and proliferate but also enlarge and undergo phenotypic changes (4, 5).Although much attention has been devoted to sprouting angiogenesis in cancer, less is known about the factors that govern vascular remodeling in inflammation. The microvasculature of the mouse trachea presents an opportunity to study such factors because it (a) has a regular segmented 2D architecture repeated between and over the tracheal cartilage rings; (b) can be subjected to short-and long-lasting inflammatory stimuli (6); and (c) is a site of angiogenesis, vascular remodeling, and lymphangiogenesis after infection by Mycoplasma pulmonis. A conspicuous early feature of vascular remodeling in the ...

Angiogenesis inhibitors that block vascular endothelial growth factor receptor (VEGFR) signaling slow the growth of many types of tumors, but eventually the disease progresses. Multiple strategies are being explored to improve efficacy by concurrent inhibition of other functionally relevant receptor tyrosine kinases (RTKs). XL880 (foretinib, GSK1363089) and XL184 (cabozantinib) are small molecule inhibitors that potently block multiple RTKs including VEGFR and the receptor of hepatocyte growth factor c-Met, which can drive tumor invasion and metastasis. This study compared the cellular effects of XL880 and XL184 to those of an RTK inhibitor (XL999) that blocks VEGFR but not c-Met. Treatment of RIP-Tag2 mice with XL999 resulted in 43% reduction in vascularity of spontaneous pancreatic islet tumors over 7 days, but treatment with XL880 or XL184 eliminated ~ 80% of the tumor vasculature, reduced pericytes and empty basement membrane sleeves, caused widespread intratumoral hypoxia and tumor cell apoptosis, and slowed regrowth of the tumor vasculature after drug withdrawal. Importantly, XL880 and XL184 also decreased invasiveness of primary tumors and reduced metastasis. Overall, these findings indicate that inhibition of c-Met and functionally related kinases amplifies the effects of VEGFR blockade and leads to rapid, robust, and progressive regression of tumor vasculature, increased intratumoral hypoxia and apoptosis, and reduced tumor invasiveness and metastasis.

Mice xenotransplanted with human cells and/or expressing human gene products (also known as “humanized mice”) recapitulate the human evolutionary specialization and diversity of genotypic and phenotypic traits. These models can provide a relevant in vivo context for understanding of human‐specific physiology and pathologies. Humanized mice have advanced toward mainstream preclinical models and are now at the forefront of biomedical research. Here, we considered innovations and challenges regarding the reconstitution of human immunity and human tissues, modeling of human infections and cancer, and the use of humanized mice for testing drugs or regenerative therapy products. As the number of publications exploring different facets of humanized mouse models has steadily increased in past years, it is becoming evident that standardized reporting is needed in the field. Therefore, an international community‐driven resource called “Minimal Information for Standardization of Humanized Mice” ( MISHUM ) has been created for the purpose of enhancing rigor and reproducibility of studies in the field. Within MISHUM , we propose comprehensive guidelines for reporting critical information generated using humanized mice.

Rationale: Lymphatic vessels in the respiratory tract normally mature into a functional network during the neonatal period, but under some pathological conditions can grow as enlarged, dilated sacs that result in the potentially lethal condition of pulmonary lymphangiectasia. Objective: We sought to determine whether overexpression of the lymphangiogenic growth factor VEGF-C can promote lymphatic growth and maturation in the respiratory tract. Unexpectedly, perinatal overexpression of VEGF-C in the respiratory epithelium led to a condition resembling human pulmonary lymphangiectasia, a life-threatening disorder of the newborn characterized by respiratory distress and the presence of widely dilated lymphatics. Methods and Results: Administration of doxycycline to CCSP-rtTA/tetO-VEGF-C double transgenic mice during a critical period from E15.5 to P14 was accompanied by respiratory distress, chylothorax, pulmonary lymphangiectasia, and high mortality. Enlarged sac-like lymphatics were abundant near major airways, pulmonary vessels, and visceral pleura. Side-by-side comparison revealed morphologic features similar to pulmonary lymphangiectasia in humans. The condition was milder in mice given doxycycline after age P14 and did not develop after P35. Mechanistic studies revealed that VEGFR-3 alone drove lymphatic growth in adult mice, but both VEGFR-2 and VEGFR-3 were required for the development of lymphangiectasia in neonates. VEGFR-2/VEGFR-3 heterodimers were more abundant in the dilated lymphatics, consistent with the involvement of both receptors. Despite the dependence of lymphangiectasia on VEGFR-2 and VEGFR-3, the condition was not reversed by blocking both receptors together or by withdrawing VEGF-C. Conclusions: The findings indicate that VEGF-C overexpression can induce pulmonary lymphangiectasia during a critical period in perinatal development.