Facial nerve regeneration via body-brain crosstalk: The role of stem cells and biomaterials

The human body is a complex, integral whole, and disruptions in one organ can lead to dysfunctions in other parts of the organ network. The facial nerve, as the seventh cranial nerve, arises from the brainstem, controls facial expression muscles and plays a crucial role in brain-body communication. This vulnerable nerve can be damaged by trauma, inflammation, tumors, and congenital diseases, often impairing facial expression. Stem cells have gained significant attention for repairing peripheral nerve injuries due to their multidirectional differentiation potential. Additionally, various biomaterials have been used in tissue engineering for regeneration and repair. However, the therapeutic potential of stem cells and biomaterials in treating facial nerve injuries requires further exploration. In this review, we summarize the roles of stem cells and biomaterials in the regeneration and repair of damaged facial nerves, providing a theoretical basis for the recovery and reconstruction of body-brain crosstalk between the brain and facial expression muscles.

Research status of facial nerve repair

The facial nerve, also known as the seventh cranial nerve, is critical in controlling the movement of the facial muscles. It is responsible for all facial expressions, such as smiling, frowning, and moving the eyebrows. However, damage to this nerve can occur for a variety of reasons, including maxillofacial surgery, trauma, tumors, and infections. Facial nerve injuries can cause severe functional impairment and can lead to different degrees of facial paralysis, significantly affecting the quality of life of patients. Over the past ten years, significant progress has been made in the field of facial nerve repair. Different approaches, including direct suture, autologous nerve grafts, and tissue engineering, have been utilized for the repair of facial nerve injury. This article mainly summarizes the clinical methods and basic research progress of facial nerve repair in the past ten years.

Physiological Responses Induced by Manual Therapy in Animal Models: A Scoping Review

Background: Physiological responses related to manual therapy (MT) treatment have been investigated over decades using various animal models. However, these studies have not been compiled and their collective findings appraised. The purpose of this scoping review was to assess current scientific knowledge on the physiological responses related to MT and/or simulated MT procedures in animal models so as to act as a resource to better inform future mechanistic and clinical research incorporating these therapeutic interventions.

Methods: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane, Embase, and Index of Chiropractic Literature (ICL) were searched from database inception to August 2019. Eligible studies were: (a) published in English; (b) non-cadaveric animal-based; (c) original data studies; (d) included a form of MT or simulated MT as treatment; (e) included quantification of at least one delivery parameter of MT treatment; (f) quantification of at least one physiological measure that could potentially contribute to therapeutic mechanisms of action of the MT. MT studies were categorized according to three main intervention types: (1) mobilization; (2) manipulation; and (3) massage. Two-phase screening procedures were conducted by a pair of independent reviewers, data were extracted from eligible studies and qualitatively reported.

Results: The literature search resulted in 231 articles of which 78 met inclusion criteria and were sorted by intervention type. Joint mobilization induced changes in nociceptive response and inflammatory profile, gene expression, receptor activation, neurotransmitter release and enzymatic activity. Spinal manipulation produced changes in muscle spindle response, nocifensive reflex response and neuronal activity, electromyography, and immunologic response. Physiological changes associated with massage therapy included autonomic, circulatory, lymphatic and immunologic functions, visceral response, gene expression, neuroanatomy, function and pathology, and cellular response to in vitro simulated massage.

Conclusion: Pre-clinical research supports an association between MT physiological response and multiple potential short-term MT therapeutic mechanisms. Optimization of MT delivery and/or treatment efficacy will require additional preclinical investigation in which MT delivery parameters are controlled and reported using pathological and/or chronic pain models that mimic neuromusculoskeletal conditions for which MT has demonstrated clinical benefit.

Reconstruction of Multiple Facial Nerve Branches Using Skeletal Muscle-Derived Multipotent Stem Cell Sheet-Pellet Transplantation

Head and neck cancer is often diagnosed at advanced stages, and surgical resection with wide margins is generally indicated, despite this treatment being associated with poor postoperative quality of life (QOL). We have previously reported on the therapeutic effects of skeletal muscle-derived multipotent stem cells (Sk-MSCs), which exert reconstitution capacity for muscle-nerve-blood vessel units. Recently, we further developed a 3D patch-transplantation system using Sk-MSC sheet-pellets. The aim of this study is the application of the 3D Sk-MSC transplantation system to the reconstitution of facial complex nerve-vascular networks after severe damage. Mouse experiments were performed for histological analysis and rats were used for functional examinations. The Sk-MSC sheet-pellets were prepared from GFP-Tg mice and SD rats, and were transplanted into the facial resection model (ST). Culture medium was transplanted as a control (NT). In the mouse experiment, facial-nerve-palsy (FNP) scoring was performed weekly during the recovery period, and immunohistochemistry was used for the evaluation of histological recovery after 8 weeks. In rats, contractility of facial muscles was measured via electrical stimulation of facial nerves root, as the marker of total functional recovery at 8 weeks after transplantation. The ST-group showed significantly higher FNP (about three fold) scores when compared to the NT-group after 2–8 weeks. Similarly, significant functional recovery of whisker movement muscles was confirmed in the ST-group at 8 weeks after transplantation. In addition, engrafted GFP⁺ cells formed complex branches of nerve-vascular networks, with differentiation into Schwann cells and perineurial/endoneurial cells, as well as vascular endothelial and smooth muscle cells. Thus, Sk-MSC sheet-pellet transplantation is potentially useful for functional reconstitution therapy of large defects in facial nerve-vascular networks.

Fluorescently labeled peptide increases identification of degenerated facial nerve branches during surgery and improves functional outcome

Nerve degeneration after transection injury decreases intraoperative visibility under white light (WL), complicating surgical repair. We show here that the use of fluorescently labeled nerve binding probe (F-NP41) can improve intraoperative visualization of chronically (up to 9 months) denervated nerves. In a mouse model for the repair of chronically denervated facial nerves, the intraoperative use of fluorescent labeling decreased time to nerve identification by 40% compared to surgeries performed under WL alone. Cumulative functional post-operative recovery was also significantly improved in the fluorescence guided group as determined by quantitatively tracking of the recovery of whisker movement at time intervals for 6 weeks post-repair. To our knowledge, this is the first description of an injectable probe that increases visibility of chronically denervated nerves during surgical repair in live animals. Future translation of this probe may improve functional outcome for patients with chronic denervation undergoing surgical repair.

Mandibular branch of the facial nerve in wistar rats: new experimental model to assess facial nerve regeneration

Introduction The ideal animal model for nerve regeneration studies is the object of controversy, because all models described by the literature have advantages and disadvantages.

Objective To describe the histologic and functional patterns of the mandibular branch of the facial nerve of Wistar rats to create a new experimental model of facial nerve regeneration.

Methods Forty-two male rats were submitted to a nerve conduction test of the mandibular branch to obtain the compound muscle action potential. Twelve of these rats had the mandibular branch surgically removed and submitted to histologic analysis (number, partial density, and axonal diameter) of the proximal and distal segments.

Results There was no statistically significant difference in the functional and histologic variables studied.

Conclusion These new histologic and functional standards of the mandibular branch of the facial nerve of rats establish an objective, easy, and greatly reproducible model for future facial nerve regeneration studies.

Bone marrow stem cells in facial nerve regeneration from isolated stumps

INTRODUCTION

Severe lesions in the facial nerve may have extensive axonal loss and leave isolated stumps that impose technical difficulties for nerve grafting.

METHODS

We evaluated bone marrow stem cells (BMSC) in a silicone conduit for rat facial nerve regeneration from isolated stumps. Group A utilized empty silicone tubes; in groups B-D, the tube was filled with acellular gel; and, in groups C and D, undifferentiated BMSC (uBMSC) or Schwann-like cells differentiated from BMSC (dBMSC) were added, respectively. Compound muscle action potentials (CMAPs) were measured, and histology was evaluated.

RESULTS

Groups C and D had the highest CMAP amplitudes. Group C had shorter CMAP durations than groups A, B, and D. Distal axonal number and density were increased in group C compared with groups A and B.

CONCLUSIONS

Regeneration of the facial nerve was improved by both uBMSC and dBMSC in rats, yet uBMSC was associated with superior functional results.

Use of nerve conduits for peripheral nerve injury repair: A Web of Science-based literature analysis

OBJECTIVE:

To identify global research trends in the use of nerve conduits for peripheral nerve injury repair.

DATA RETRIEVAL:

Numerous basic and clinical studies on nerve conduits for peripheral nerve injury repair were performed between 2002–2011. We performed a bibliometric analysis of the institutions, authors, and hot topics in the field, from the Web of Science, using the key words peripheral nerve and conduit or tube.

SELECTION CRITERIA:

Inclusion criteria: peer-reviewed published articles on nerve conduits for peripheral nerve injury repair, indexed in the Web of Science; original research articles, reviews, meeting abstracts, proceedings papers, book chapters, editorial material, and news items. Exclusion criteria: articles requiring manual searching or telephone access; documents not published in the public domain; and several corrected papers.

MAIN OUTCOME MEASURES:

(a) Annual publication output; (b) publication type; (c) publication by research field; (d) publication by journal; (e) publication by funding agency; (f) publication by author; (g) publication by country and institution; (h) publications by institution in China; (i) most-cited papers.

RESULTS:

A total of 793 publications on the use of nerve conduits for peripheral nerve injury repair were retrieved from the Web of Science between 2002–2011. The number of publications gradually increased over the 10-year study period. Articles constituted the main type of publication. The most prolific journals were Biomaterials, Microsurgery, and Journal of Biomedical Materials Research Part A. The National Natural Science Foundation of China supported 27 papers, more than any other funding agency. Of the 793 publications, almost half came from American and Chinese authors and institutions.

CONCLUSION:

Nerve conduits have been studied extensively for peripheral nerve regeneration; however, many problems remain in this field, which are difficult for researchers to reach a consensus.

Use of a Y-Tube Conduit After Facial Nerve Injury Reduces Collateral Axonal Branching at the Lesion Site But Neither Reduces Polyinnervation of Motor Endplates Nor Improves Functional Recovery

BACKGROUND:

Despite increased understanding of peripheral nerve regeneration, functional recovery after surgical repair remains disappointing. A major contributing factor is the extensive collateral branching at the lesion site, which leads to inaccurate axonal navigation and aberrant reinnervation of targets.

OBJECTIVE:

To determine whether the Y tube reconstruction improved axonal regrowth and whether this was associated with improved function.

METHODS:

We used a Y-tube conduit with the aim of improving navigation of regenerating axons after facial nerve transection in rats.

RESULTS:

Retrograde labeling from the zygomatic and buccal branches showed a halving in the number of double-labeled facial motor neurons (15% vs 8%; P < .05) after Y tube reconstruction compared with facial-facial anastomosis coaptation. However, in both surgical groups, the proportion of polyinnervated motor endplates was similar (∼30%; P > .05), and video-based motion analysis of whisking revealed similarly poor function.

CONCLUSION:

Although Y-tube reconstruction decreases axonal branching at the lesion site and improves axonal navigation compared with facial-facial anastomosis coaptation, it fails to promote monoinnervation of motor endplates and confers no functional benefit.

Repair of facial nerve defects with decellularized artery allografts containing autologous adipose-derived stem cells in a rat model

The purpose of this study was to investigate the effects of a decellularized artery allograft containing autologous adipose-derived stem cells (ADSCs) on an 8-mm facial nerve branch lesion in a rat model. At 8 weeks postoperatively, functional evaluation of unilateral vibrissae movements, morphological analysis of regenerated nerve segments and retrograde labeling of facial motoneurons were all analyzed. Better regenerative outcomes associated with functional improvement, great axonal growth, and improved target reinnervation were achieved in the artery-ADSCs group (2), whereas the cut nerves sutured with artery conduits alone (group 1) achieved inferior restoration. Furthermore, transected nerves repaired with nerve autografts (group 3) resulted in significant recovery of whisking, maturation of myelinated fibers and increased number of labeled facial neurons, and the latter two parameters were significantly different from those of group 2. Collectively, though our combined use of a decellularized artery allograft with autologous ADSCs achieved regenerative outcomes inferior to a nerve autograft, it certainly showed a beneficial effect on promoting nerve regeneration and thus represents an alternative approach for the reconstruction of peripheral facial nerve defects.

Intrinsic and therapeutic factors determining the recovery of motor function after peripheral nerve transection

Insufficient recovery after peripheral nerve injury has been attributed to (i) poor pathfinding of regrowing axons, (ii) excessive collateral axonal branching at the lesion site and (iii) polyneuronal innervation of the neuromuscular junctions (NMJ). The facial nerve transection model has been used initially to measure restoration of function after varying therapies and to examine the mechanisms underlying their effects. Since it is very difficult to control the navigation of several thousand axons, efforts concentrated on collateral branching and NMJ-polyinnervation. Treatment with antibodies against trophic factors to combat branching improved the precision of reinnervation, but had no positive effects on functional recovery. This suggested that polyneuronal reinnervation--rather than collateral branching--may be the critical limiting factor. The former could be reduced by pharmacological agents known to perturb microtubule assembly and was followed by recovery of function. Because muscle polyinnervation is activity-dependent and can be manipulated, attempts to design a clinically feasible therapy were performed by electrical stimulation or by soft tissue massage. Electrical stimulation applied to the transected facial nerve or to paralysed facial muscles did not improve vibrissal motor performance and failed to diminish polyinnervation. In contrast, gentle stroking of the paralysed muscles (vibrissal, orbicularis oculi, tongue musculature) resulted in full recovery of function. This manual stimulation was also effective after hypoglossal-facial nerve suture and after interpositional nerve grafting, but not after surgical reconstruction of the median nerve. All these findings raise hopes that clinically feasible and effective therapies could be soon designed and tested.

Schwann cells overexpressing FGF-2 alone or combined with manual stimulation do not promote functional recovery after facial nerve injury

PURPOSE

To determine whether transplantation of Schwann cells (SCs) overexpressing different isoforms of fibroblast growth factor 2 (FGF-2) combined with manual stimulation (MS) of vibrissal muscles improves recovery after facial nerve transection in adult rat.

PROCEDURES

Transected facial nerves were entubulated with collagen alone or collagen plus naïve SCs or transfected SCs. Half of the rats received daily MS. Collateral branching was quantified from motoneuron counts after retrograde labeling from 3 facial nerve branches. Quality assessment of endplate reinnervation was combined with video-based vibrissal function analysis.

RESULTS

There was no difference in the extent of collateral axonal branching. The proportion of polyinnervated motor endplates for either naïve SCs or FGF-2 over-expressing SCs was identical. Postoperative MS also failed to improve recovery.

CONCLUSIONS

Neither FGF-2 isoform changed the extent of collateral branching or polyinnervation of motor endplates; furthermore, this motoneuron response could not be overridden by MS.