Age Dependence of Lung Mesenchymal Stromal Cell Dynamics Following Pneumonectomy

Abstract

Aging is a critical determinant of regenerative capacity in many organ systems, but it remains unresolved in the lung. This study examines murine lung cell dynamics during age-dependent lung regeneration. Proliferation of lung progenitor cells (EpCAM neg /Sca-1 high lung mesenchymal stromal cells -LMSCs, EpCAM pos /Sca-1 low epithelial progenitor cells, proSP-C pos alveolar type II epithelial cells -AECII, and CD31 pos -endothelial cells) was tracked to day 3 or 7 after pneumonectomy (PNX) or SHAM surgery in 3, 9, and 17 month mice. In 3 month mice, post-PNX LMSC proliferation peaked early (3 days), with 50%-80% more BrdU-positive cells than the other cell types, which peaked later (4-7 days). In older mice (9 and 17 month), abundance and post-PNX proliferation of LMSCs at day 3 were reduced (40%-80%). In both young and old mice, LMSCs were isolated and compared phenotypically with whole lung non-LMSCs. Donor age had no qualitative effect on the phenotype (LMSC vs. non-LMSC), with increased expression of CD90/Thy1, CD105/Eng, CD106/Vcam, CD146/Mcam, and Pdgfra, and up-regulation of mRNA encoding Fap, Eln, Col1a1, Col3a1, Aldh1a3, Arhgef25, Dner, Fgfr1, and Midkine. However, compared with LMSCs isolated from young mice, LMSCs from older mice exhibited reduced mRNA expression of retinoic acid (Aldh1a3, Rbp4), Fgf/Wnt (Fgfr1, Sfrp1, Wnt2, and Ctnnb1), and elastogenesis (Col1a1, Eln, Fbn1, and Sdc2) pathway genes. Isolated LMSCs from older mice also demonstrated lower colony-forming units ( -67%), growth potential ( -60% by day 7), ALDH activity ( -49%), and telomerase activity ( -47%). Therefore, age is associated with declining proliferative potential and regenerative functions of LMSCs in the lung.

Comparative analysis of the mechanical signals in lung development and compensatory growth

“…Alveolar type-2 (AT2) cells are the first progenitors to proliferate and hypertrophy (Hsia and Johnson, 2006, Thet and Law, 1984). Other stem or progenitor cell types have not shown significant or reliable response (Nolen-Walston, et al, 2008, Paxson, et al, 2013, Voswinckel, et al, 2003). It is highly unlikely for a single or a few progenitor cell types alone to account for the intensity, rapidity and widespread spatial distribution of post-PNX proliferative response.…”

Hallmarks of the ageing lung

“…However, others have reported decreased hematopoietic progenitors, but unchanged numbers of circulating endothelial progenitor cells in COPD patients [119,120]. Moreover, dysfunction of other potential progenitor cell types, such as mesenchymal stromal cells (MSCs), has been associated with reduced repair capacity in a murine post-pneumectomy model [121]. BUSTOS et al [122] found diminished anti-inflammatory potential of bone marrow-derived MSCs from old mice.…”

Mesenchymal stromal cell turnover in the normal adult lung revisited

“…By employing a simple and robust noninvasive method of continuous in vivo long-term BrdU labeling (8,9) to mathematically model the cell kinetic behavior of well-characterized flow cytometrically isolated lung mesenchymal stromal cells we have demonstrated that the mesenchymal stromal cells in the mouse lung are not quiescent in the steady state but cycle continuously to maintain lung tissue homeostasis in response to normal wear and tear and participate in reactivation of the epithelial-mesenchymal trophic unit in remodeling the lung in response to insult or injury (2,22,31,32,39,40). In normal unperturbed C57Bl/6 adult mice, CD45 neg CD31…”

“…Others have also noted the relative absence of BrdU-incorporating lung stromal cells on microscopic examination of the airway and alveolar parenchyma of the uninjured lung (31 (32,38), but immunohistomorphometric discrimination of BrdU-labeled mesenchymal stromal cells in those settings would be confounded by autofluorescence and by the emergence of mesenchymal phenotypes whose relationship to those found in the steady state is unclear (34,35).…”

“…Early studies reviewed by Kauffman (23) and by Evans and Shami (17) showed that the labeling index of lung interstitial fibroblasts in situ increased sharply to levels up to 8 -10 times higher than that of juxtaposed epithelial cells during perinatal lung growth and alveolar septation and then rapidly declined. Recent analysis of lung regeneration in adult mice postpneumonectomy also reveals a rapid but transient increase in the proliferative activity of lung mesenchymal stromal cells in the days immediately following surgery, predominantly associated with the alveolar parenchyma (31,32). However, values for the labeling index or the level of BrdU incorporation in adult lung interstitial cells in the steady state are rarely reported and then typically range from undetectable to less than 0.2% (20,31,38).…”