Reversing Lung Diseases By Directing Stem Cell Differentiation

Lung diseases can scar the respiratory tissues necessary for oxygen exchange. Without proper oxygen exchange, our cells lack the means to make the energy they so desperately need, and they begin to shut down or even die. Lung diseases such as asthma, emphysema, chronic obstructive pulmonary disease and others can permanently diminish lung capacity, life expectancy and activity levels.

Fortunately, a preclinical study in laboratory animals has suggested a new strategy for treating lung diseases. Carla Kim and Joo-Hyeon Lee of the Stem Cell Research Program at Boston Children’s have described a new lung-specific pathway that is activated by lung injury and directs a resident stem cell population in the lung to proliferate and differentiate into lung-specific cell types.

When Kim and Lee enhanced this pathway in mice, they observed increase production of the cells that line the alveolar sacs where gas exchange occurs. Alveolar cells are irreversibly damaged in emphysema and pulmonary fibrosis.

Inhibition of this same pathway increased stem cell-mediated production of airway epithelial cells, which line the passages that conduct air to the alveolar sacs and are damaged in asthma and bronchiolitis obliterans.

For their experiments, Kim and Lee used a novel culture system called a 3D culture system that mimics the milieu of the lung. This culture system showed that a single bronchioalveolar stem cell could differentiate into both alveolar and bronchiolar epithelial cells. By adding a protein called TSP-1 (thrombospondin-1), the stem cells differentiated into alveolar cells.

Next, Kim and Lee utilized a mouse model of pulmonary fibrosis. However, when they cultured the small endothelial cells that line the many small blood vessels in the lung, which naturally produce TSP-1, and directly injected the culture fluid of these cells into the mice, the noticed these injections reverse the lung damage.

When they used lung endothelial cells that do not produce TSP-1 in 3D cultures, lung-specific stem cells produce more airway cells. in mice that were engineered to not express TSP-1, airway repair was enhanced after lung injury.

Lung Stem Cell Repair of Lung Damage

Lee explained his results in this way: “When the lung cells are injured, there seems to be a cross talk between the damaged cells, the lung endothelial cells and the stem cells.”

Kim added: “We think that lung endothelial cells produce a lot of repair factors besides TSP-1. We want to find all these molecules, which could provide additional therapeutic targets.”

Even though this work is preclinical in nature, it represents a remarkable way to address the lung damage that debilitates so many people. Hopefully this work is easily translatable to human patients and clinical trials will be in the future. Before that, more confirmation of the role of TSP-1 is required.

Stem Cells Heal Damaged Cells by Transferring Mitochondria

An Indian team from Delhi, India has identified a protein that increases the transfer of mitochondria from mesenchymal stem cells to lung cells, thus augmenting the healing of lung cells.

Stem cells like mesenchymal stem cells from bone marrow, fat, tendons, liver, skeletal muscle, and so on secrete a host of healing molecules, but they also form bridges to other cells and export their own mitochondria to heal damaged cells. Mitochondria are the structures inside cells that make energy. Damaged cells can have serious energy deficiencies and mitochondrial transfer ameliorates such problems (see Cárdenes N et al, Respiration. 2013;85(4):267-78).

This present work from the laboratory of Anurag Agrawal, who is housed in the Centre of Excellence in Asthma & Lung Disease, at the CSIR‐Institute of Genomics and Integrative Biology in Delhi, India has identified a protein called Miro1 that regulates the transfer of mitochondria to recipient cells.

Mitochondrial transfer has so many distinct benefits that stem cell scientists hope to engineer stem cells to transfer more of their mitochondria to damaged cells, and Miro1 might be a target for such stem cell engineering experiments.

Mitochondrial transfer between stem cells and other cells occurs by means of tunneling nanotubes, which are thread-like structures formed from the plasma membranes of cells that form bridges between different cell types. Under stressful conditions, the number of these nanotubes increases.

In the present study. stem cells engineered to express more Miro1 protein transferred mitochondria more efficiently than control stem cells. When used in mice with damaged lungs and airways, these Miro1-overexpressing cells were therapeutically more effective than control cells.

This study presents the first mechanistic insight into how Mesenchymal Stem Cells (MSC) act as mitochondrial donors during attenuation of lung inflammation and injury. Mitochondrial donation is an essential part of the MSC therapeutic effect in these models and is positively regulated by Miro1 / Rhot1 mitochondrial transport proteins.
This study presents the first mechanistic insight into how Mesenchymal Stem Cells (MSC) act as mitochondrial donors during attenuation of lung inflammation and injury. Mitochondrial donation is an essential part of the MSC therapeutic effect in these models and is positively regulated by Miro1 / Rhot1 mitochondrial transport proteins.

The hope is to use Miro1 manipulations to make better stem cell therapies for human diseases.

To summarize this work:

1. MSCs donate mitochondria to stressed epithelial cells (EC) that have malfunctioning mitochondrial.  Cytoplasmic nanotubular bridges form between the cells and Miro‐1 mediated mitochondrial transfer occurs unidirectionally from MSCs to ECs.

2. Other mesenchymal cells like smooth muscle cells and fibroblasts express Miro1 and can also donate mitochondria to ECs, but with low efficiency. ECs have very low levels of Miro1 and, as a rule, do not donate mitochondria.

3. Enhanced expression of Miro1 in mesenchymal cells increases their mitochondrial donor efficiency.  Conversely, cells lacking Miro1 do not show MSC mediated mitochondrial donation.

4. Miro1‐overexpressing MSCs have enhanced therapeutic effects in three different models of allergic lung inflammation and rat poison-induced lung injury.  Conversely, Miro1‐depleted MSCs lose much of their therapeutic effect.  Miro1 overexpression in MSCs may lead to more effective stem cell therapy.

Human Stem Cells Converted into Functional Lung Cells

Scientists from the Columbia University Medical Center have succeeded in transforming human stem cells into functional lung and airway cells. This finding has significant potential for modeling lung disease, screening lung-specific drugs, and, hopefully, generating lung tissue for transplantation.

Study leader, Hans-Willem Snoeck, professor of medicine and affiliated with the Columbia Center for Translational Immunology and the Columbia Stem Cell Initiative, said, “Researchers have had relative success in turning human stem cells into heart cells, pancreatic beta cells, intestinal cells, liver cells, and nerve cells, raising all sorts of possibilities for regenerative medicine. Now, we are finally able to make lung and airway cells. This is important because lung transplants have a particularly poor prognosis. Although any clinical application is still many years away, we can begin thinking about making autologous lung transplants – that is, transplants that use a patient’s own skin cells to generate functional lung tissue.”

The research builds on Snoeck’s earlier discoveries in 2011 that a set of chemical factors could induce the differentiation of embryonic or induced pluripotent stem cells into “anterior foregut endoderm,” which is the embryo in the tissue from which the lungs form (Green MD, et al. Generation of anterior foregut endoderm from human embryonic and induced pluripotent stem cells. Nat Biotechnol. 2011 Mar;29(3):267-72).

Human Embryological Development - one month

In his new study, Snoeck and his colleagues found new factors that can transform anterior foregut endoderm cells into lung and airway cells. In particular, Snoeck and his co-workers were able to establish the presence of “type 2 alveolar epithelial cells,” which secrete the lung surfactant that maintains the lung alveoli (those tiny sacs in the lung where all the oxygen exchange takes place).

lung alveolus

With these techniques, lung researchers hope to study diseases like idiopathic pulmonary fibrosis (IPF), in which type 2 epithelial cells seem to divide and produce scarring in the lungs.

“No one knows what causes the disease, and there’s no way to treat it,” said Snoeck. “Using this technology, researchers will finally be able to create laboratory models of IPF, study the disease at the molecular level, and screen drugs for possible treatments or cures. In the longer term, we hope to use this technology to make an autologous lung graft. This would entail taking a lung from a donor, removing all the lung cells, leaving only the lung scaffold; and seeding the scaffold with new lung cells derived from the patient. In this way, rejection problems could be avoided.”

Snoeck is investigating this approach in collaboration with researchers in the Columbia University Department of Biomedical Engineering.