Stem Cells Reduce Pain, Improve Bladder

Posted by Sam Maddox in Research News on October 12, 2016 # Research

A group at the University of California San Francisco reported in late September that human embryonic stem cells, transplanted to the area of injury in an animal model, integrated functionally in the mouse spinal cord, and differentiated into a cell type that quieted amped-up nerve signals. The result: reduction of pain and improvement of bladder function.

The work comes from a group led by Arnold Kriegstein, a physician/scientist who is founding director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at UCSF, along with Linda Noble-Haeusslein, Departments of Neurological Surgery and Physical Therapy and Rehabilitation Science at UCSF.

Said Kriegstein, "We reasoned if we could take inhibitory neurons and directly place them into the spinal cord in the regions that are overactive, they might integrate into those circuits and suppress the activity."

Before getting into the pith of the report, let’s acknowledge the front-line role UCSF has played in the stem cell world, going back 35 years to the actual naming of isolated single cells from the inner mass of an embryonic blastocyst. Gail Martin, professor emeritus at UCSF, called them “embryonic stem cells.” The history of human embryonic stem cells (hESC) is generally pegged to 1998, when the Thomson lab in Wisconsin isolated the cells and coaxed them from embryos into robust cell lines. Martin, years earlier, differentiated her single cells into a wide variety of cell types; she didn’t grow them in perpetuity, but she deserves more than an asterisk.

UCSF is also the U.S. home base for Shinya Yamanaka, a professor of anatomy at the university as well as senior investigator at the affiliated Gladstone Institutes. Yamanaka figured out how to make ordinary skin cells into reproducible, pluripotent cells that are very much like hESC – without the embryo. He won the 2012 Nobel Prize in Physiology or Medicine for his discovery of induced pluripotent stem cells.

Back to the Kriegstein study. The normal nervous system runs on electro-chemical reactions, finely tuned and balanced with regard to inhibitory or excitatory activity. Injury, of course, can dramatically affect that balance. GABA is a neurotransmitter that in the adult nervous system inhibits nerve activity. Glutamate, for example, is just the opposite; it excites activity. Glutamate gets its share of research (in many ways trying to limit it; a clinical trial sponsored in part by the Reeve Foundation continues to test a glutamate-reducing drug, riluzole.)

Loss of nerve cells that activate GABA signaling contributes to common symptoms of SCI: neuropathic pain and loss of bladder coordination, which are attributed in part to overactive spinal cord circuits. You can take a GABA agonist, a drug that might improve neurotransmission, but these drugs (including barbiturates, baclofen, and some steroids) often come with lots of side effects.

Kriegstein et al asked the question, what if these so-called GABAergic cells could be restored, or perhaps replaced? Might that recalibrate a degree of balance in the system, and perhaps represent a meaningful therapy for people living with spinal cord injury? If so, how might one introduce a new cell that acts like a lost one?

Their answer: embryonic stem cells cultured in a way to be GABAergic. Technically, the cells are called medial ganglionic eminence (MGE) precursors; what’s important is that they enhance GABA signals.

From the paper, titled Transplanted Human Stem Cell-Derived Interneuron Precursors Mitigate Mouse Bladder Dysfunction and Central Neuropathic Pain after Spinal Cord Injury.

We find that six months after transplantation into injured mouse spinal cords, hESC-MGEs differentiate into GABAergic neuron subtypes and receive synaptic inputs, suggesting functional integration into host spinal cord. Moreover, the transplanted animals show improved bladder function and mitigation of pain-related symptoms. Our results therefore suggest that this approach may be a valuable strategy for ameliorating the adverse effects of spinal cord injury.

Here’s what they did. They first transplanted the human stem cells into the lumbar cord of uninjured animals. If this had affected either bladder function or motor behavior, it would have been cause for concern. But it didn’t. Next, they transplanted the same hESC into mice, two weeks after a thoracic injury.

First author Thomas Fandel: "Rather than implanting these cells into the site of injury, at the mid-thoracic level, we injected them in the lumbosacral region, where the circuits are known to be overactive. Six months later we could see broad dispersion of the cells in that area. They were integrated into the spinal cord."

The new cells survived, were dispersed 10 mm up and down from the transplant site, became GABAergic neurons, and wired themselves in to form functional synapses in the local circuitry. They weren’t looking for motor recovery and there was none.

So. GABA source restored. What about pain? From the paper:

SCI may result in chronic allodynia [pain from touch, for example, which would normally not create pain] and hyperalgesia [heightened pain sensitivity] .... Spinal cord-injured mice developed tactile allodynia and thermal hyperalgesia at two weeks post-injury that was sustained over an observation period of six months. Cell transplantation alleviated tactile allodynia at both three and six months post-transplantation, and it alleviated hyperalgesia at six months post-transplantation.

And bladder?

There was a decrease in maximal voiding pressure, in the number of non-voiding contractions, and in residual urine in the hESC-MGE group. Correspondingly, voiding efficiency was improved and there was less bladder over-distension. Improvements in bladder function in transplanted animals were associated with a reduction in aberrant remodeling of the bladder wall, including hypertrophy of its detrusor muscle layer, relative to vehicle controls. Together these data demonstrate that hESC-MGE-transplanted animals show reduced bladder outlet resistance and detrusor overactivity, which correspond to improved voiding function.

To summarize:

We demonstrate disease-modifying capabilities of hESC-MGEs in a pre-clinical model of SCI. The hESC-MGEs survive, migrate, differentiate into GABAergic neuron subtypes, functionally integrate into local circuitry, reduce CNP, and ameliorate bladder dysfunction after SCI.

Clinical relevance: Possibly, certainly in the acute model. Does it mean anything to the chronic SCI world? Maybe. First, keep in mind these studies in mice may not predict similar results for people.

Chronics? The UCSF group thinks that could happen, and frames its optimism, with an eye on other research groups hoping to restore motor function:

Other groups have proposed human stem cell-derived therapeutic candidates, including projection neurons and oligodendroglia, for transplantation directly into the spinal cord-injured segment, with a focus on restoration of locomotor recovery. In contrast, our approach involves delivery of local interneuron precursors below the level of injury. In the future, it may be of interest to combine both therapeutic strategies in an attempt to maximize patient recovery.

Unlike the spinal cord-injured segment that undergoes extensive remodeling including cavitation over time, the below-injury gray matter may continue to support donor cell engraftment into the chronic phase. Our findings, therefore, may have implications for the treatment of chronically spinal cord-injured patients. However, before the initiation of clinical trials for subacute or chronic SCI patients can be considered, several preclinical development milestones must be achieved, including identification of a good manufacturing practice (GMP)-grade human ESC line, determination of a tolerable and efficacious dosing range, and demonstration of safety in both small and large animals.

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