Human multilineage-differentiating stress enduring (Muse) cells, a novel nontumorigenic pluripotent-like stem cell population, reside in the bone marrow, skin and adipose tissues, and can be collected as cells positive for stage-specific embryonic antigen-3 (SSEA-3), a surface marker for human embryonic stem cells. There are approximately 1% of SSEA-3-positive Muse cells in bone marrow-derived mesenchymal stem cells (BM-MSCs) [Ref.1]. Thus, we investigated the effects of locally administered human Muse cells on bladder tissues, function and nociceptive behavior in a chemically induced interstitial cystitis (IC)-like rat model.

Chemical cystitis was induced by intravesical instillation of 0.2N hydrochloride (HCl) for 15 minutes in female F344 rats. Muse cells, non-Muse cells (BM-MSCs without Muse cells) or Hanks' balanced salt solution (HBSS) (vehicle) were injected into the anterior and posterior bladder wall at each 1x10^4 cells/10μL 6 hours after HCl application whereas controls received bladder wall injection of HBSS without HCl instillation. Changes in urinary frequency were evaluated before and 1 week after the injection using metabolic cages. In addition, nociceptive behavior (freezing) induced by intravesical instillation of 1mM capsaicin, and histological changes in expression of tissue necrotic factor α (TNFα) in the urothelium / lamina propria and c-Fos in the dorsal horn of L6 spinal cord were examined 1 week after the injection in each group. In other animal groups, cystometrograms 1 week after the injection, and survival of Muse or non-Muse cells labelled by a fluorescent marker, mCherry in the bladder 1,2 and 4 weeks after the injection were also evaluated.

There were significant increases in urinary frequency of vehicle and non-Muse cell groups, but not of the Muse cell group, compared with controls (Fig.1A). Significant increases in nociceptive behavior and expression of TNFα and c-Fos were observed in vehicle and non-Muse cell groups compared with controls whereas these significant changes were not seen in the Muse cell group (Fig.1B, C, D). In cystometrograms, bladder capacity was significantly decreased in vehicle and non-Muse cell groups, but not in the Muse cell group, compared with controls. In addition, a larger number of Muse cells survived in the urothelial basal layer or lamina propria compared with non-Muse cells until 4 weeks (Fig.2).

In the present study, human Muse cell treatment ameliorated bladder inflammation, bladder overactivity, and nociception in a rat model of chemically induced cystitis, as similarly reported in a previous study with bladder wall injection of rodent adipose-derived MSCs [Ref.2]. Currently, clinical trials using human Muse cell-product, CL2020 are ongoing for the treatments of myocardial infarction, cerebral infarction, spinal cord injury, epidermolysis bullosa, neonatal hypoxic-ischemic encephalopathy and amyotrophic lateral sclerosis.

These results indicate that locally administered human Muse cells significantly reduced bladder inflammation, resulting in improvement of bladder dysfunction such as urinary frequency and bladder pain in a chemically induced IC-like rat model. The Muse cell therapy could be a promising modality to treat IC, especially Hunner type IC with severe bladder pain due to chronic inflammation.

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