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.

Nanotubules Link Damaged Heart Cells With Mesenchymal Stem Cells to Both of Their Benefit


Mesenchymal stem cells are found throughout the body in bone marrow, fat, tendons, muscle, skin, umbilical cord, and many other tissues. These cells have the capacity to readily differentiate into bone, fat, and cartilage, and can also form smooth muscles under particular conditions.

Several animal studies and clinical trials have demonstrated that mesenchymal stem cells can help heal the heart after a heart attack. Mesenchymal stem cells (MSCs) tend to help the heart by secreting a variety of particular molecules that stimulate heart muscle survival, proliferation, and healing.

Given these mechanisms of healing, is there a better way to get these healing molecules to the heart muscle cells?

A research group from INSERM in Creteil, France has examined the use of tunneling nanotubes to connect MSCs with heart muscle cells. These experiments have revealed something remarkable about MSCs.

Florence Figeac and her colleagues in the laboratory of Ann-Marie Rodriguez used a culture system that grew fat-derived MSCs and with mouse heart muscle cells. They induced damage in the heart muscle cells and then used tunneling nanotubes to connect the fat-based MSCs.

They discovered two things. First of all, the MSCs secreted a variety of healing molecules regardless of their culture situation. However, when the MSCs were co-cultured with damaged heart muscle cells with tunneling nanotubes, the secretion of healing molecules increased. The tunneling nanotubes somehow passed signals from the damaged heart muscle cells to the MSCs and these signals jacked up secretion of healing molecules by the MSCs.

The authors referred to this as “crosstalk” between the fat-derived MSCs and heart muscle cells through the tunneling nanotubes and it altered the secretion of heart protective soluble factors (e.g., VEGF, HGF, SDF-1α, and MCP-3). The increased secretion of these molecules also maximized the ability of these stem cells to promote the growth and formation of new blood vessels and recruit bone marrow stem cells.

After these experiments in cell culture, Figeac and her colleagues used these cells in a living animal. They discovered that the fat-based MSCs did a better job at healing the heart if they were previously co-cultured with heart muscle cells.

Exposure of the MSCs to damaged heart muscle cells jacked up the expression of healing molecules, and therefore, these previous exposures made these MSCs better at healing hearts in comparison to naive MSCs that were not previously exposed to damaged heart muscle.

Thus, these experiments show that crosstalk between MSCs and heart muscle cells, mediated by nanotubes, can optimize heart-based stem cells therapies.