Spatial dependence of alveolar angiogenesis in post-pneumonectomy lung growth

Abstract

Growth of the remaining lung after pneumonectomy has been observed in many mammalian species; nonetheless, the pattern and morphology of alveolar angiogenesis during compensatory growth is unknown. Here, we investigated alveolar angiogenesis in a murine model of post-pneumonectomy lung growth. As expected, the volume and weight of the remaining lung returned to near-baseline levels within 21 days of pneumonectomy. The percentage increase in lobar weight was greatest in the cardiac lobe (p<.001). Cell cycle flow cytometry demonstrated a peak of lung cell proliferation (12.02±1.48%) 6 days after pneumonectomy. Spatial autocorrelation analysis of the cardiac lobe demonstrated clustering of similar vascular densities (positive autocorrelation) that consistently mapped to subpleural regions of the cardiac lobe. Immunohistochemical staining demonstrated increased cell density and enhanced expression of angiogenesis-related factors VEGFA, and GLUT1 in these subpleural regions. Corrosion casting and scanning electron microscopy 3-6 days after pneumonectomy demonstrated subpleural vessels with angiogenic sprouts. The monopodial sprouts appeared to be randomly oriented along the vessel axis with interbranch distances of 11.4±4.8 um in the regions of active angiogenesis. Also present within the regions of increased vascular density were frequent “holes” or “pillars” consistent with active intussusceptive angiogenesis. The mean pillar diameter was 4.2±3.8 um and the pillars were observed in all regions of active angiogenesis. These findings indicate that the process of alveolar construction involves discrete regions of regenerative growth, particularly in the subpleural regions of the cardiac lobe, characterized by both sprouting and intussusceptive angiogenesis.

Remodeling of alveolar septa after murine pneumonectomy

“…We estimate that 20 -30% of alveolar ducts in the cardiac lobe demonstrated retracted septa on day 3 after pneumonectomy. These results are consistent with previous findings of noncontiguous regions of alveolar angiogenesis in the subpleural cardiac lobe (1,23).…”

Inhibition of Notch signaling induces extensive intussusceptive neo-angiogenesis by recruitment of mononuclear cells

“…Compared to sprouting angiogenesis, intussusception is relatively fast, thus allowing swift vascular adaptation in compromised conditions. In liver regeneration models and in postpneumonectomy alveolar angiogenesis, intussusception has been identified as the predominant mode of growth, and also in extraembryonic vasculatures including the vitelline circulation, intussusception appears to prevail over sprouting [7][8][9]. Surprisingly, the cellular and molecular regulation of intussusception is less well known, but recent evidence suggests that it might involve components regulated by blood flow and Notch signaling [6,7].…”

Role of Notch, SDF-1 and Mononuclear Cells Recruitment in Angiogenesis

“…IA has been identified as the leading mode of vascular growth in animal models of liver regeneration and in alveolar angiogenesis following pneumonectomy. Intussusception appears to be predominant above sprouting in extra-embryonic vasculatures including the vitelline circulation as well [8][9][10]. The intensive work of our group in the past few decades clearly documented the morphological features of this specific angiogenic mode and demonstrated its definite presence during development and tumorigenesis as a complementary to sprouting vessel growth.…”

“…Intussusceptive angiogenesis is a process linked to both blood vessel replication and remodeling in development. It is present within the regions of increased vascular density in alveolar angiogenesis during compensatory growth after pneumonectomy in a murine model of postpneumonectomy lung growth [8]. The remodeling of the retiform meshworks in the avian lung was essentially accomplished by intussusceptive angiogenesis as well [12].…”