Gut-derived factors promote neurogenesis of CNS-neural stem cells and nudge their differentiation to an enteric-like neuronal phenotype

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

White paper on guidelines concerning enteric nervous system stem cell therapy for enteric neuropathies

Over the last 20 years, there has been increasing focus on the development of novel stem cell based therapies for the treatment of disorders and diseases affecting the enteric nervous system (ENS) of the gastrointestinal tract (so-called enteric neuropathies). Here, the idea is that ENS progenitor/stem cells could be transplanted into the gut wall to replace the damaged or absent neurons and glia of the ENS. This White Paper sets out experts' views on the commonly used methods and approaches to identify, isolate, purify, expand and optimize ENS stem cells, transplant them into the bowel, and assess transplant success, including restoration of gut function. We also highlight obstacles that must be overcome in order to progress from successful preclinical studies in animal models to ENS stem cell therapies in the clinic.

New approaches to increase intestinal length: Methods used for intestinal regeneration and bioengineering

Inadequate absorptive surface area poses a great challenge to the patients suffering a variety of intestinal diseases causing short bowel syndrome. To date, these patients are managed with total parenteral nutrition or intestinal transplantation. However, these carry significant morbidity and mortality. Currently, by emergence of tissue engineering, anticipations to utilize an alternative method to increase the intestinal absorptive surface area are increasing. In this paper, we will review the improvements made over time in attempting elongating the intestine with surgical techniques as well as using intestinal bioengineering. Performing sequential intestinal lengthening was the preliminary method applied in humans. However, these methods did not reach widespread use and has limited outcome. Subsequent experimental methods were developed utilizing scaffolds to regenerate intestinal tissue and organoids unit from the intestinal epithelium. Stem cells also have been studied and applied in all types of tissue engineering. Biomaterials were utilized as a structural support for naive cells to produce bio-engineered tissue that can achieve a near-normal anatomical structure. A promising novel approach is the elongation of the intestine with an acellular biologic scaffold to generate a neo-formed intestinal tissue that showed, for the first time, evidence of absorption in vivo. In the large intestine, studies are more focused on regeneration and engineering of sphincters and will be briefly reviewed. From the review of the existing literature, it can be concluded that significant progress has been achieved in these experimental methods but that these now need to be fully translated into a pre-clinical and clinical experimentation to become a future viable therapeutic option.

Stem cell therapy for GI neuromuscular disorders

The enteric nervous system is the intrinsic innervation of the gut. Several neuromuscular disorders affect the neurons and glia of the enteric nervous system adversely, resulting in disruptions in gastrointestinal motility and function. Pharmacological interventions to remedy gastrointestinal function do not address the underlying cause of dysmotility arising from lost, absent, or damaged enteric neuroglial circuitry. Cell-based therapies have gained traction in the past decade, following the discovery of several adult stem cell niches in the human body. Adult neural stem cells can be isolated from the postnatal and adult intestine using minimally invasive biopsies. These stem cells retain the ability to differentiate into several functional classes of enteric neurons and enteric glia. Upon identification of these cells, several groups have also established that transplantation of these cells into aganglionic or dysganglionic intestine rescues gastrointestinal motility and function. This chapter highlights key studies performed in the field of stem cell transplantation therapies that are targeted towards the remedy of gastrointestinal motility and function.

Enteric neural progenitors are more efficient than brain-derived progenitors at generating neurons in the colon

Gut motility disorders can result from an absent, damaged, or dysfunctional enteric nervous system (ENS). Cell therapy is an exciting prospect to treat these enteric neuropathies and restore gut motility. Previous studies have examined a variety of sources of stem/progenitor cells, but the ability of different sources of cells to generate enteric neurons has not been directly compared. It is important to identify the source of stem/progenitor cells that is best at colonizing the bowel and generating neurons following transplantation. The aim of this study was to compare the ability of central nervous system (CNS) progenitors and ENS progenitors to colonize the colon and differentiate into neurons. Genetically labeled CNS- and ENS-derived progenitors were cocultured with aneural explants of embryonic mouse colon for 1 or 2.5 wk to assess their migratory, proliferative, and differentiation capacities, and survival, in the embryonic gut environment. Both progenitor cell populations were transplanted in the postnatal colon of mice in vivo for 4 wk before they were analyzed for migration and differentiation using immunohistochemistry. ENS-derived progenitors migrated further than CNS-derived cells in both embryonic and postnatal gut environments. ENS-derived progenitors also gave rise to more neurons than their CNS-derived counterparts. Furthermore, neurons derived from ENS progenitors clustered together in ganglia, whereas CNS-derived neurons were mostly solitary. We conclude that, within the gut environment, ENS-derived progenitors show superior migration, proliferation, and neuronal differentiation compared with CNS progenitors.

The influence of extracellular matrix composition on the differentiation of neuronal subtypes in tissue engineered innervated intestinal smooth muscle sheets

Differentiation of enteric neural stem cells into several appropriate neural phenotypes is crucial while considering transplantation as a cellular therapy to treat enteric neuropathies. We describe the formation of tissue engineered innervated sheets, where intestinal smooth muscle and enteric neuronal progenitor cells are brought into close association in extracellular matrix (ECM) based microenvironments. Uniaxial alignment of constituent smooth muscle cells was achieved by substrate microtopography. The smooth muscle component of the tissue engineered sheets maintained a contractile phenotype irrespective of the ECM composition, and generated equivalent contractions in response to potassium chloride stimulation, similar to native intestinal tissue. We provided enteric neuronal progenitor cells with permissive ECM-based compositional and viscoelastic cues to generate excitatory and inhibitory neuronal subtypes. In the presence of the smooth muscle cells, the enteric neuronal progenitor cells differentiated to functionally innervate the smooth muscle. The differentiation of specific neuronal subtypes was influenced by the ECM microenvironment, namely combinations of collagen I, collagen IV, laminin and/or heparan sulfate. The physiology of differentiated neurons within tissue engineered sheets was evaluated. Sheets with composite collagen and laminin had the most similar patterns of Acetylcholine-induced contraction to native intestinal tissue, corresponding to an increased protein expression of choline acetyltransferase. An enriched nitrergic neuronal population, evidenced by an increased expression of neuronal nitric oxide synthase, was obtained in tissue engineered sheets that included collagen IV. These sheets had a significantly increased magnitude of electrical field stimulated relaxation, sensitive maximally to nitric oxide synthase inhibition. Tissue engineered sheets containing laminin and/or heparan sulfate had a balanced expression of contractile and relaxant motor neurons. Our studies demonstrated that neuronal subtype was modulated by varying ECM composition. This observation could be utilized to derive enriched populations of specific enteric neurons in vitro prior to transplantation.

Tissue engineering in the gut: developments in neuromusculature

The complexity of the gastrointestinal (GI) tract lies in its anatomy as well as in its physiology. Several different cell types populate the GI tract, adding to the complexity of cell sourcing for regenerative medicine. Each cell layer has a specialized function in mediating digestion, absorption, secretion, motility, and excretion. Tissue engineering and regenerative medicine aim to regenerate the specific layers mimicking architecture and recapitulating function. Gastrointestinal motility is the underlying program that mediates the diverse functions of the intestines, as an organ. Hence, the first logical step in GI regenerative medicine is the reconstruction of the tubular smooth musculature along with the drivers of their input, the enteric nervous system. Recent advances in the field of GI tissue engineering have focused on the use of scaffolding biomaterials in combination with cells and bioactive factors. The ability to innervate the bioengineered muscle is a critical step to ensure proper functionality. Finally, in vivo studies are essential to evaluate implant integration with host tissue, survival, and functionality. In this review, we focus on the tubular structure of the GI tract, tools for innervation, and, finally, evaluation of in vivo strategies for GI replacements.

Achalasia

Achalasia is a rare motility disorder of the oesophagus characterised by loss of enteric neurons leading to absence of peristalsis and impaired relaxation of the lower oesophageal sphincter. Although its cause remains largely unknown, ganglionitis resulting from an aberrant immune response triggered by a viral infection has been proposed to underlie the loss of oesophageal neurons, particularly in genetically susceptible individuals. The subsequent stasis of ingested food not only leads to symptoms of dysphagia, regurgitation, chest pain, and weight loss, but also results in an increased risk of oesophageal carcinoma. At present, pneumatic dilatation and Heller myotomy combined with an anti-reflux procedure are the treatments of choice and have comparable success rates. Per-oral endoscopic myotomy has recently been introduced as a new minimally invasive treatment for achalasia, but there have not yet been any randomised clinical trials comparing this option with pneumatic dilatation and Heller myotomy.

Neo-innervation of a bioengineered intestinal smooth muscle construct around chitosan scaffold

Neuromuscular disorders of the gut result in disturbances in gastrointestinal transit. The objective of this study was to evaluate the neo-innervation of smooth muscle in an attempt to restore lost innervation. We have previously shown the potential use of composite chitosan scaffolds as support for intestinal smooth muscle constructs. However, the constructs lacked neuronal component. Here, we bioengineered innervated colonic smooth muscle constructs using rabbit colon smooth muscle and enteric neural progenitor cells. We also bioengineered smooth muscle only tissue constructs using colonic smooth muscle cells. The constructs were placed next to each other around tubular chitosan scaffolds and left in culture. Real time force generation conducted on the intrinsically innervated smooth muscle constructs showed differentiated functional neurons. The bioengineered smooth muscle only constructs became neo-innervated. The neo-innervation results were confirmed by immunostaining assays. Chitosan supported (1) the differentiation of neural progenitor cells in the constructs and (2) the neo-innervation of non-innervated smooth muscle around the same scaffold.

Transplantation of enteric neural stem/progenitor cells into the irradiated young mouse hippocampus

Radiotherapy is an effective treatment for brain tumors but often results in cognitive deficits in survivors. Transplantation of embryonic or brain-derived neural stem/progenitor cells (BNSPCs) ameliorated cognitive impairment after irradiation (IR) in animal models. However, such an approach in patients requires a clinically relevant source of cells. We show for the first time the utilization of enteric neural stem/progenitor cells (ENSPCs) from the postnatal intestinal wall as a source of autologous cells for brain repair after injury caused by IR. Cells were isolated from the intestinal wall and propagated in vitro for 1 week. Differentiation assays showed that ENSPCs are multipotent and generated neurons, astrocytes, and myofibroblasts. To investigate whether ENSPCs can be used in vivo, postnatal day 9 mice were subjected to a single moderate irradiation dose (6 or 8 Gy). Twelve days later, mice received an intrahippocampal injection of syngeneic ENSPCs. Four weeks after transplantation, 0.5% and 1% of grafted ENSPCs were detected in the dentate gyrus of sham and irradiated animals, respectively, and only 0.1% was detected after 16 weeks. Grafted ENSPCs remained undifferentiated but failed to restore IR-induced loss of BNSPCs and the subsequent impaired growth of the dentate gyrus. We observed microglia activation, astrogliosis, and loss of granule neurons associated with grafted ENSPC clusters. Transplantation of ENSPCs did not ameliorate IR-induced impaired learning and memory. In summary, while autologous ENSPC grafting to the brain worked technically, even in the absence of immunosuppression, the protocols need to be modified to improve survival and integration.

Intestinal tissue engineering: current concepts and future vision of regenerative medicine in the gut

Functional tissue engineering of the gastrointestinal (GI) tract is a complex process aiming to aid the regeneration of structural layers of smooth muscle, intrinsic enteric neuronal plexuses, specialized mucosa, and epithelial cells as well as interstitial cells. The final tissue-engineered construct is intended to mimic the native GI tract anatomically and physiologically. Physiological functionality of tissue-engineered constructs is of utmost importance while considering clinical translation. The construct comprises of cellular components as well as biomaterial scaffolding components. Together, these determine the immune response a tissue-engineered construct would elicit from a host upon implantation. Over the last decade, significant advances have been made to mitigate adverse host reactions. These include a quest for identifying autologous cell sources like embryonic and adult stem cells, bone marrow-derived cells, neural crest-derived cells, and muscle derived-stem cells. Scaffolding biomaterials have been fabricated with increasing biocompatibility and biodegradability. Manufacturing processes have advanced to allow for precise spatial architecture of scaffolds to mimic in vivo milieu closely and achieve neovascularization. This review will focus on the current concepts and the future vision of functional tissue engineering of the diverse neuromuscular structures of the GI tract from the esophagus to the internal anal sphincter.