At present, more and more registrations for a variety of diseases support the therapeutic benefits of MSC transplantation in clinical trials (www.clinicaltrials.gov). In contrast, the registrations of MenSCs are still few, and no more than 10 clinical trials are presented by searching “menstrual blood stem cells”. Actually, the therapeutic potential of MenSCs has already been recognized in several kinds of diseases in pre-clinical research, which is fundamental for future clinical applications in tissue repair and regenerative medicine. Similar to BM-MSCs, MenSCs also have several merits, including the ability to migrate into injury sites, differentiation into different cell lineages, secretion of soluble factors, and regulation of immune responses. Therefore, more researches need to be explored before MenSC becomes a common use in clinical application and treatment.

Liver disease

Liver fibrosis is the universal phase of various chronic liver diseases and causes a huge public health issue due to high rates for the morbidity and mortality worldwide [50]. Fibrosis was a reversible process along with wound healing and characterized by accumulation of ECM protein at the site of an injured liver [51]. At present, orthotopic liver transplantation (OLT) is the most effective strategy for patients at the end stage of liver disease. However, due to lack of organ donors, surgical complications, lifelong immunosuppression, and high cost, its application has been limited to a large number of patients in the current condition. Recently, we have studied the therapeutic effect of MenSC transplantation in a mouse model of liver fibrosis induced by CCl 4 (carbon tetrachloride) [20]. The results showed that MenSC had the effect on treating liver fibrosis. Liver function was improved via targeting activated hepatic stellate cells (HSCs), and collagen deposition was reduced after cell transplantation in liver fibrotic mice. Co-culture experiments showed that MenSCs restrained the proliferation of LX-2 cells (HSC line) through secretion of paracrine cytokines, including interleukin-6 (IL-6), IL-8, hepatocyte growth factor (HGF), monocyte chemoattractant protein 1 (MCP-1), growth-related oncogene (GRO), and osteoprotegerin (OPG). The results suggest that MenSC may be an attractive treatment for chronic liver disease by targeting HSCs via paracrine mediators.

Fulminant hepatic failure (FHF) is a life-threatening and sharply pathological reaction, which results in relatively high mortality by rapid necrosis of liver cells with the stimulation of a variety of acute injuries, such as hepatotoxic drugs, immune-mediated attacks, or viral infections [52]. The exosomes contain microRNA/lncRNA and adhesion molecules as well as small vesicles of secreted proteins, which mediate cellular signaling pathways both in vivo and in vitro [53]. Our group proved that MenSC-derived exosomes (MenSC-Ex) possessed therapeutic potential by inhibiting hepatocyte apoptosis in D-galactosamine (D-Gal) and lipopolysaccharide (LPS) induced FHF in mice, and we further showed that the levels of TNF-α, IL-6, and IL-1β were reduced by co-culture with AML12 hepatocytes (a normal mouse hepatocyte cell line) in vitro [19]. The study suggests that MenSC-Ex can improve liver function to increase the rate of survival in FHF model mice.

Diabetes

Type 1 diabetes mellitus (T1DM), known as a kind of autoimmune diabetes, is a multifactorial disease by the deficiency of secreting insulin in islet β cells to influence the normal organism metabolism, ultimately leading to elevated blood glucose levels and a severe decline in insulin secretion [54]. Transplantation of human islets is currently the most effective treatment; due to the lack of pancreatic donors, it has been greatly restricted in the widespread application. Our team has studied the therapeutic effect of MenSCs and the underlying mechanism of β cell regeneration after MenSC transplantation in the T1DM mouse model [35]. From our study, MenSCs could facilitate β-cell regeneration and enhance the number of β cells by increasing the expressions of neurogenin 3 (ngn 3), forkhead box A2 (foxa 2), pancreatic and duodenal homeobox 1 (pdx 1), NK homeobox factor 6.1 (nkx 6.1), and paired box gene (pax) to activate endogenous progenitor cell differentiation post MenSC transplantation in T1DM mice. Clarifying the precise mechanism involved in MenSC-induced β-cell regeneration will facilitate the future use of MenSCs to treat diabetes.

Ischemic stroke

Ischemic stroke, one of the leading causes of long-term disability, is a chain reaction of functional impairment that initially occurs during the identification phase of rapid physical and mental fluctuations [55]. Currently, ischemic stroke causes many patients producing permanent nerve damage, and stem cell therapy will help to improve and possibly restore the nerve function. Borlongan et al. demonstrated that MenSCs improved ischemic stroke in an oxygen glucose deprivation (OGD) rat model in vitro [40]. The behavioral and histological disorders were also significantly improved in the rat model of ischemic stroke by intracerebral/intravenous transplantation. Co-culture experiments showed that MenSCs significantly reduced cell death of OGD-exposed rat primary neurons through increasing vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3). The neurostructural and behavioral benefits afforded by transplanted MenSCs support their use as a kind of stem cell source for cell therapy in treating ischemic stroke.

Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a deadly x-linked muscle degeneration disease that consists of a potential genetic defect characterized by an enhanced inflammatory response [56]. DMD is an important part of the muscular dystrophy glycoprotein complex (DGC), which is involved in the relative stabilization of the sarcolemma and regulation of the interaction between the cytoskeleton and skeletal muscle and myocardial ECM. Umezawa’s team showed that MenSCs could restore muscle degeneration and repair skeletal muscle abnormalities by increasing muscle-like protein expression in immunodeficient DMD model mice [13]. In addition, MenSCs effectively differentiated into myoblasts/muscle cells after co-culture with mouse myoblast C2C12 in vitro, and these differentiated cells could express anti-atrophy muscle protein. It is suggested that MenSCs transform muscular dystrophic cells into anti-atrophic cells through trans-differentiation both in vitro and in vivo.

Critical limb ischemia

Critical limb ischemia (CLI) refers to the final clinical stage along with the limb damage due to severe blood loss causing a series of pathological and physiological abnormalities that lead to limb pain or insufficient nutrition to support the legs [57]. Currently, although clinical trials have reported that autologous stem cells improve their symptoms by stimulating angiogenesis, the appropriate cell population of MSCs is still needed to explore. Murphy et al. demonstrated that administration of MenSCs improved CLI in a mouse model [58]. Although they did not explore the precise mechanism, they pointed out three possible reasons: (1) producing high levels of growth factors, IL-4, hypoxia inducible factor-1 alpha (HIF-1α), and matrix metalloproteinases (such as MMP3 and MMP10) with a paracrine role; (2) inhibiting the inflammatory response and blocking the pro-inflammatory signaling pathway; (3) producing a large amount of endothelial progenitor cells to mediate cell differentiation. Collectively, they suggest that MenSC represents a novel approach for treating the CLI by supplying an “off the shelf” therapeutic way, and it will provide a guideline for the feasibility of the proposed clinical trial in future.

Ovarian-related disease

Ovarian cancer is one of the most deadly gynecological diseases for ambiguous symptoms and lack of reliable screening methods in many developed countries [59]. At present, platinum-based combination chemotherapy is the standard treatment for the past decade, but there is almost no improvement and progress. Cancer patients, especially women under the age of 40, are often suffering from reproductive damage related with premature ovarian failure (POF) and infertility in women. Lai et al. have demonstrated that MenSCs improved the estrous cycle and restored mouse fertility in the POF mouse model [36]. Wang et al. further explored that MenSCs could significantly improve the ovarian microenvironment by reducing granulosa cell apoptosis and ovarian interstitial fibrosis [21]. Transplanted MenSCs played an important role in ovarian function by secreting cytokines such as fibroblast growth factor 2 (FGF 2). MenSCs repair ovarian injury, improve ovarian function, and stimulate ovarian regeneration, which suggest that MenSCs may be a novel and effective strategy for the treatment of POF in regenerative medicine.

In addition, epithelial ovarian cancer (EOC) has been found to be advanced in most cases, with a combination of extensive abdominal metastasis, high recurrence, and chemoresistance [60]. Recently, Lai group found that MenSCs could improve the symptoms of EOC through tumor transplant animal model in vivo. Moreover, they further discovered that MenSCs induced angiogenic ability by inhibiting AKT/PKB (protein kinase B)-mediated degradation of the forkhead O-3a (FoxO3a) to induce cell cycle arrest, promote apoptosis, interfere with mitochondrial membrane function, and reduce EOC cells in co-culture models in vitro. These results suggest that MenSCs inhibit AKT-induced degradation of FoxO3a, which facilitates the anti-tumor properties of MenSCs on EOC in future regenerative medicine.

Myocardial infarction

Myocardial infarction (MI), a type of coronary artery disease (CAD), is pathologically defined as the death of cardiomyocytes because of excessive ischemic condition [61]. Since MI has a long-term undiscovered phase, it can also be a major catastrophic event that causes sudden death or severe hemodynamic deterioration in patients. Hida et al. confirmed that the transplanted MenSCs significantly restored the damaged cardiac function in nude rat model [45]. In addition, Jiang et al. further demonstrated that MenSCs significantly reduced apoptosis, promoted cell proliferation, and recruited c-kit+ cells in an immunological MI model rats [29]. MenSCs could express some specific cytokines to activate AKT/extracellular signal-regulated kinases 1 and 2 (ERK 1/2)/signal transducers and activator of transcription 3 (STAT 3) and suppress p38 signaling pathway. Then Wang’s team found that MenSCs inhibited endothelial cell to mesenchymal transition (EMT), which helped to reduce the total number of cardiac fibroblasts and tissue fibrosis progression [62]. In addition, they verified that secreted exosomes of miR-21 mediated and enhanced the paracrine and cytoprotective effects through a transwell co-culture system in vitro. Exosomal microRNA (miR) array revealed that miR-21 targeted phosphatase and tensin homolog (PTEN) and the downstream of AKT [37]. These results suggest that MenSCs improve the damaged cardiac function in MI mainly through paracrine role and miRs deriving from exosome.

Asherman syndrome

Asherman syndrome is caused by the formation of adhesions in the uterine cavity. Women with this disease often have many comprehensive and complicated symptoms, such as infertility, irregular menstruation (including amenorrhea, less menstruation, or dysmenorrhea), and repeated pregnancy loss [63]. Autologous MenSC transplantation significantly increased endometrial thickness (ET) in Asherman syndrome women in a total of 7 patients with Asherman syndrome in a non-controlled prospective and 3-year clinical study [28]. They showed that the ET of 5 women was significantly increased to 7 mm (a thickness to ensure embryo implantation). Four of these patients were subjected to frozen embryo transfer (FET). Surprisingly, one patient developed a spontaneous pregnancy only after the second MenSC transplant. This study suggests that autologous MenSC transplantation is a possible option for the treatment of Asherman syndrome in women.

Alzheimer’s disease

Alzheimer’s disease, caused by amyloid-beta (Aβ) production, is progressive memory loss and cognitive dysfunction, and its neuropathological features are induced by the hyperphosphorylated tau proteins, which are composed of extracellular Aβ plaque deposits and intracellular neurofibrillary tangles (NTFs) [64]. Our group found that transplantation of MenSC in the brain of APP/PS1 mice could significantly improve the spatial learning characteristics and memory ability of AD in mouse model [34]. In addition, MenSCs significantly improved amyloid plaques in vivo and reduced tau hyperphosphorylation. It is worth noting that we also proved that intracranial transplantation of MenSCs significantly increased the expression of Aβ-degrading enzymes and decreased the level of pro-inflammatory cytokines to alter the microglia-associated phenotype. This result indicates that MenSCs can degrade Aβ and play an anti-inflammatory effect for improving AD in vivo.

Acute lung injury

Acute lung injury (ALI) is a severe health burden worldwide due to its rapid attack and high mortality. Many factors can cause ALI, such as tidal volume, mechanical ventilation, or hypoxia; these injuries are often accompanied by inflammatory reactions, and once inflammatory reactions are sustained, the patients will face suffocation or even death [65]. Our group showed that MenSCs promoted the repair of injured lung by inhibiting the inflammatory response in LPS-induced ALI in mice [38]. Furthermore, MenSCs not only improved pulmonary microvascular permeability, reduced histopathological injury, and downregulated the expressions of IL-1β and caspase-3, but also upregulated the levels of IL-10, proliferating cell nuclear antigen (PCNA), and keratinocyte growth factor (KGF) in bronchoalveolar lavage fluid (BALF). MenSCs could also increase the survival rate of BEAS-2B cells (human normal lung epithelial cells) and inhibit LPS-induced cell apoptosis in a co-culture experiment. These results suggest that MenSC-based treatment may become an attractive strategy for improving ALI in regenerative medicine.

Cutaneous wound

Cutaneous wound is repaired by coordinated biological progress to restore the original stage of damaged tissue, including cell proliferation and differentiation, and a variety of cell apoptosis, thereby producing multiple layers of connective tissue. The repaired skin is usually cured in the form of a scar, and the main purposes of the cutaneous regeneration are to understand how to induce skin to reconstruct damaged parts without forming scars [66]. Cuenca et al. revealed that MenSCs significantly improved wound healing and enhanced new blood vessel formation in a mouse excisional wound model [41]. They further discovered that MenSCs secreted some cytokines, including angiopoietin (Angpt), platelet-derived growth factor (PDGF), elastin (Eln), MMP3, and MMP10, allowing them to participate in wound repair. These results suggest that MenSCs promote wound healing and contribute to cutaneous regeneration.

Endometriosis

Endometriosis is a common gynecological disorder defined as endometrial glands and interstitial growth outside the uterus, which is currently present in approximately 10% of women at reproductive age and 30% of infertile women [67]. Clinical interest and research are mainly focused on lesions and the directly affected diseases for the lack of understanding and exploration of the pathogenesis of women in different periods. Nikoo et al. found that MenSCs played a very important role by comparing the ability in morphology, CD marker expression, cell proliferation, invasion, adhesion, and some immunomodulatory molecules between women with endometriosis (E-MenSCs) and non-endometriosis (NE-MenSCs) [27]. In addition, the expressions of indoleamine 2,3-dioxygenase-1 (IDO1), cyclooxygenase-2 (COX-2), IFN-γ, IL-10, and MCP-1 were increased, and the level of forkhead transcription factor-3 (FOXP3) was reduced in co-culture of E-MenSCs and peripheral blood mononuclear cells (PBMCs) in vitro. These finding suggests that MenSC has a critical role in improving endometriosis.