doi:10.1038/nindia.2014.136 Published online 16 October 2014
Medical Researchers in Mumbai claim to have found novel stem cells capable of regenerating damaged mouse pancreas. They hope these cells called "Very Small Embryonic-like Stem Cells" or VSELs could be manipulated to treat diabetes1.
Pancreas is the source of insulin, the hormone which acts to lower blood sugar. In type-1 diabetes, the pancreas no longer makes insulin and patients have to take insulin injections lifelong. A cell therapy to regenerate and coax the diabetic pancreas to produce insulin has been the dream of stem cell researchers worldwide. Now Deepa Bhartiya, who heads the Stem Cell Biology Department at the National Institute for Research in Reproductive Health (NIRRH) in Mumbai, says her laboratory "has an edge in this field internationally."
The researchers carried out a study in an adult mouse, 70 per cent of whose pancreas had been removed by surgery. They identified the presence of VSELs in small numbers in the normal pancreas before surgery. However, after partial-pancreatectomy large numbers of them got mobilized and were found involved in regeneration of the damaged pancreas. "Detection of VSELs in situ in normal adult pancreas and their involvement during regeneration in the present study suggest that VSELs could open a way to regenerate diabetic pancreas in humans in future," the researchers conclude.
Spherical in shape and slightly smaller than red blood cells in size, the VSELs are pluripotent, Bhartiya told Nature India. In other words, they have the ability to self-renew and give rise to tissue-specific progenitors which can differentiate into cells of all three germ layers (ectoderm, mesoderm and endoderm found in the early embryo) that eventually mature into the body's major organs, including the pancreas.
"Besides the pancreas, we have seen and reported the VSELs in ovary, testis, cord blood, bone marrow and Wharton’s jelly of the umbilical cord," she said and added: "Being pluripotent, the VSELs can potentially transform regenerative medicine. "Regenerative medicine currently relies on pluripotent stem cells that are either extracted from a very early stage embryo (ES cells), or from adult cells that have been induced into a pluripotent state (iPS cells).
"We have results to show that VSELs may be better than ES or iPS cells in their ability to differentiate into adult counterparts." A challenge for ES cell-based product is potential immune rejection by the patient and risk of teratoma formation — this is where VSELs may score over attempts by other groups working on cell therapy to treat diabetes using ES cells.
Besides, the cost will be much less by manipulating endogenous (autologus) stem cells compared to ES/iPS cells which are grown in Petri dish and require GMP facility. "Manipulating endogenous stem cells will target Type-2 diabetes which has a greater disease burden compared to Type-1," Bhartiya said.
Other studies reported by Bhartiya's team found that VSELs exist in mouse testis as well as in the ovaries. Ovarian VSELs spontaneously differentiate into egg-like structures in vitro. The VSELs in both testis and ovaries were found to survive chemotherapy — good news for cancer survivors. While cancer drugs killed the germ cells in the testis, the surviving VSELs "could restore sperm formation when we provided a healthy somatic niche2."
As a corollary to these findings in mouse ovary and testis, Bhartiya’s group has proposed that surviving VSELs may serve as potential source of autologus gametes (sperm and eggs) that may enable individuals rendered infertile due to cancer treatment, injuries or other reasons have their own biological child. "If we could manipulate the surviving VSELs in vivo in cancer survivors, the existing need to bank ovarian or testicular tissue/gametes prior to cancer treatment, ethical and epigenetic/genetic concerns associated with in vitro culture to obtain gametes will be minimized," Bhartiya said.
The VSELs were first described3 in mouse bone marrow in 2006, by a team led by Mariusz Ratajczak at the University of Louisville in Kentucky, USA. The team reported that the rare cell type exist in all adult organs in the body. However, owing to their very small size VSELs have remained obscure, poorly studied and their existence itself has been questioned. "There are very few global groups that are firm believers of VSELs," Satish Totey, CEO of Kasiak Research Pvt Ltd, a Mumbai-based stem cell company told Nature India.
"This is still a debatable issue and needs in-depth study before it is ready for commercial use." Jyotsana Dhawan, another stem cell expert at the Centre for Cellular and Molecular Biology in Hyderabad says. "The whole field of VSELs is in flux — real proof of their existence is wanting."
Bhartiya is not discouraged by the skepticism. "One needs to see the VSELs to believe in them. If you don't believe, come to our lab and we will show you the VSELs," she says adding that failure by other groups to see them is mainly because the tiny cells tend to get unknowingly discarded while processing. The pluripotency of VSELs cannot be doubted, she says, as they express nuclear OCT-4 (octamer-binding transcription factor-4) — the most crucial marker for pluripotent state — besides other markers at both mRNA and protein level. "In fact, we have shown their remarkable ability to regenerate adult mouse testis after chemotherapy and adult pancreas after partial pancreatectomy," says Bhartiya.
"This is in contrast to emerging literature that ES cells are differentiating into their fetal counterparts and thus may prove to be inefficient to regenerate adult organs." Bhartiya, who has 4 PhD students working on different aspects of VSELs biology, says her group is convinced that these stem cells are best candidates for regenerative medicine. "Both the risk of teratoma formation and immune-rejection associated with ES cells do not exist with VSELs," she said.
"We also have data to show4 that these are normal body stem cells which get transformed into cancer stem cells but more research is required to show this conclusively". Despite the promise Bhartiya's further research critically depends on funding which she says has declined after she switched from ES cells to VSELs apparently because the jury is still out on VSELs.
"We have a Stem Cell Task Force which both supports research and solicits proposals for ‘next-stage’ support after stringent peer review," Krishnaswami Vijay Raghavan, Secretary to the India's Department of Biotechnology, one of the agencies that has been funding Bhartiya's research, told Nature India. The VSELs related research by Bhartiya's group is (being) reviewed in this task-force, he said.