Neurotrophic factors and corneal nerve regeneration

Bilayer Cylindrical Conduit Consisting of Electrospun Polycaprolactone Nanofibers and DSC Cross-Linked Sodium Alginate Hydrogel to Bridge Peripheral Nerve Gaps

Herein, a bilayer cylindrical conduit (P-CA) is presented consisting of electrospun polycaprolactone (PCL) nanofibers and sodium alginate hydrogel covalently cross-linked with N,N'-disuccinimidyl carbonate (DSC). The bilayer P-CA conduit is developed by combining the electrospinning and outer-inner layer methods. Using DSC, as a covalent crosslinker, increases the degradation time of the sodium alginate hydrogel up to 2 months. The swelling ratio of the hydrogel is also 503% during the first 8 h. The DSC cross-linked sodium alginate in the inner layer of the conduit promotes the adhesion and proliferation of nerve cells, while the electrospun PCL nanofibers in the outer layer provide maximum tensile strength of the conduit during surgery. P-CA conduit promotes the migration of Schwann cells along the axon in a rat model based on functional and histological evidences. In conclusion, P-CA conduit will be a promising construct for repairing sciatic nerves in a rat model.

Acupoint selection for the treatment of dry eye: A systematic review and meta-analysis of randomized controlled trials

The effectiveness of acupuncture in the treatment of dry eye has been confirmed, but the association between acupoint selection and therapeutic effect has remained to be elucidated. In the present study, a systematic review and meta-analysis were performed to evaluate the effect of periocular acupoints and periocular acupoints plus body acupoints compared with AT for the treatment of dry eye disease (DED). The PubMed, Cochrane Library, Embase, Ovid, China National Knowledge Infrastructure and Chonqing VIP Information, Co., Ltd. databases were searched with entries until 10 July 2018 considered. Only randomized controlled trials (RCTs) were included. Meta-analyses were performed to compare the effects of acupuncture with those of conventional treatment (including AT or other non-acupuncture therapies). The primary outcomes, including tear break-up time (BUT), Schirmer's I test (SIT) result and Symptom scores were analyzed. Subgroup analysis was performed for periocular acupoints only and periocular acupoints plus body acupoints. A total of 12 studies comprising 900 participants were included. In the primary meta-analysis, a significant improvement in the BUT [n=1,209, weighted mean difference (WMD)=1.01, 95% CI: 0.56-1.84, P<0.00001], SIT result (n=1,107, WMD=1.98, 95% CI: 0.44-3.34, P<0.00001) and Symptom scores (n=402, WMD=-1.02, 95% CI: -1.33 to -0.72, P<0.00001) was obtained to evaluate the clinical efficacy of acupuncture and AT. Furthermore, periocular acupoints plus body acupoints were more effective in the treatment of DED. However, the total sample size of subjects with only periocular acupoints in the treatment of DED was too small to get any firm conclusions. Further large RCTs are warranted.

Unique and overlapping effects of triiodothyronine (T3) and thyroxine (T4) on sensory innervation of the chick cornea

Multiple aspects of cornea development, including the innervation of the cornea by trigeminal axons, are sensitive to embryonic levels of thyroid hormone (TH). Although previous work showed that increased TH levels could enhance the rate of axonal extension within the cornea in a thyroxine (T4)-dependent manner, details underlying the stimulatory effect of TH on cornea innervation are unclear. Here, by examining the effects throughout all stages of cornea innervation of the two main THs, triiodothyronine (T3) and T4, we provide a more complete characterization of the stimulatory effects of TH on corneal nerves and begin to unravel the underlying molecular mechanisms. During development, trigeminal axons are initially repelled at the corneal periphery and encircle the cornea in a pericorneal nerve ring prior to advancing into the corneal stroma radially from all along the nerve ring. Overall, exogenous T3 led to pleiotropic effects throughout all stages of cornea innervation, whereas the effects of exogenous T4 was confined to timepoints following completion of the nerve ring. Specifically, exogenous T3 accelerated the formation of the pericorneal nerve ring. By utilizing in vitro neuronal explants studies we demonstrated that T3 acts as a trophic factor to directly stimulate trigeminal nerve growth. Further, exogenous T3 caused disorganized and precocious innervation of the cornea, accompanied by the downregulation of inhibitory Robo receptors that normally act to regulate the timing of nerve advancement into the Slit-expressing corneal tissues. Following nerve ring completion, the growth rate and branching behavior of nerves as they advanced into and through the cornea were found to be stimulated equally by T3 or T4. These stimulatory influences of T3/T4 over nerves likely arose as secondary consequences brought on by TH-mediated modulations to the corneal extracellular matrix. Specifically, we found that the levels of nerve-inhibitory keratan- and chondroitin-sulfate containing proteoglycans and associated sulfation enzymes were dramatically altered in the presence of exogenous T3 or T4. Altogether, these findings uncover new roles for TH on corneal development and shed insight into the mechanistic basis of both T3 and T4 on cornea innervation.

The effect of human platelet lysate on corneal nerve regeneration

AIM

This study aimed to test whether human platelet lysate (HPL) has neurotrophic ability for corneal nerve regeneration.

METHODS

We measured the neurotrophic factors in human peripheral serum (HPS) and two commercially available HPLs, UltraGRO and PLTMax. In vitro, we compared the growth rates, neuronal differentiation and immunostaining of neuron markers in mouse neuroblastoma cell line (Neuro-2a) and primary culture of mouse trigeminal ganglion cells that were cultivated in different concentrations of fetal bovine serum, HPS and HPL. In vivo, we created corneal wounds on Sprague Dawley rats with a rotating burr and evaluated the effects of topical HPL on wound healing and corneal nerve regeneration by in vivo confocal microscopy and corneal aesthesiometry.

RESULTS

HPLs had significantly higher concentrations of various neurotrophic factors compared with HPS (p<0.05). In Neuro-2a cells, 3% HPL was better at promoting neuronal growth and differentiation compared with HPS at the same concentration. HPL was also found to have superior neurotrophic effects compared with HPS in primary cultures of mouse trigeminal ganglion cells. In vivo, HPL-treated eyes had better corneal epithelial wound healing rate, nerve regeneration length and corneal touch threshold compared with eyes treated with artificial tears (p<0.05).

CONCLUSION

HPL has significantly higher concentrations of neurotrophic factors compared with HPS. It showed not only in vitro but also in vivo corneal neurotrophic abilities. Our results suggest that HPL may have a potential role in the treatment of diseases related to corneal nerve damage or degeneration.

Corneal Cells: Fine-tuning Nerve Regeneration

The cornea is a transparent outermost structure of the eye anterior segment comprising the highest density of innervated tissue. In the process of corneal innervation, trigeminal ganglion originated corneal nerves diligently traverse different corneal cell types in different corneal layers including the corneal stroma and epithelium. While crossing the stromal and epithelial cell layers during innervation, due to the existing physical contacts, close interactions occur between stromal keratocytes, epithelial cells, resident immune cells and corneal nerves. Furthermore, by producing various trophic and growth factors corneal cells assist in maintaining the growth and function of corneal nerves. Similarly, corneal nerve generated growth factors critically modify the corneal cell function in all the corneal layers. Due to their close association and contacts, on-going cross-communication between these cell types and corneal nerves play a vital role in the modulation of corneal nerve function, regeneration during wound healing. The present review highlights the influence of different corneal cell types and growth factors released from these cells on corneal nerve regeneration and function.

Topical Recombinant Human Nerve Growth Factor (Cenegermin) for Neurotrophic Keratopathy: A Multicenter Randomized Vehicle-Controlled Pivotal Trial

PURPOSE

To evaluate the efficacy and safety of topical cenegermin (recombinant human nerve growth factor) in patients with neurotrophic keratopathy.

DESIGN

Multicenter, randomized, double-masked, vehicle-controlled trial.

PARTICIPANTS

Patients with neurotrophic persistent epithelial defect with or without stromal thinning.

METHODS

The NGF0214 trial, conducted among 11 sites in the United States, randomized 48 patients 1:1 to cenegermin 20 μg/ml or vehicle eye drops, 6 drops daily for 8 weeks of masked treatment. Follow-up was 24 weeks. Safety was assessed in all patients who received study drug. Efficacy was assessed by intention to treat.

MAIN OUTCOME MEASURES

The primary end point was healing of the neurotrophic lesion (persistent epithelial defect or corneal ulcer) after 8 weeks of masked treatment. Masked central readers measured neurotrophic lesions in randomized clinical pictures, then assessed healing status conventionally (<0.5 mm of fluorescein staining in the greatest dimension of the lesion area) and conservatively (0-mm lesion staining and no other residual staining). Secondary variables included corneal healing at 4 weeks of masked treatment (key secondary end point), overall changes in lesion size, rates of disease progression, and changes in visual acuity and corneal sensitivity from baseline to week 8.

RESULTS

Conventional assessment of corneal healing showed statistically significant differences at week 8: compared to 7 of 24 vehicle-treated patients (29.2%), 16 of 23 cenegermin-treated patients (69.6%) achieved less than 0.5 mm of lesion staining (+40.4%; 95% confidence interval [CI], 14.2%-66.6%; P = 0.006). Conservative assessment of corneal healing also reached statistical significance at week 8: compared to 4 of 24 vehicle-treated patients (16.7%), 15 of 23 cenegermin-treated patients (65.2%) achieved 0 mm of lesion staining and no other residual staining (+48.6%; 95% CI, 24.0%-73.1%; P < 0.001). Moreover, the conservative measure of corneal healing showed statistical significance at week 4 (key secondary end point). Compared to vehicle, cenegermin-treated patients showed statistically significant reductions in lesion size and disease progression rates during masked treatment. Cenegermin was well tolerated; adverse effects were mostly local, mild, and transient.

CONCLUSIONS

Cenegermin treatment showed higher rates of corneal healing than vehicle in neurotrophic keratopathy associated with nonhealing corneal defects.

Complement and CD4+ T cells drive context-specific corneal sensory neuropathy

Whether complement dysregulation directly contributes to the pathogenesis of peripheral nervous system diseases, including sensory neuropathies, is unclear. We addressed this important question in a mouse model of ocular HSV-1 infection, where sensory nerve damage is a common clinical problem. Through genetic and pharmacologic targeting, we uncovered a central role for C3 in sensory nerve damage at the morphological and functional levels. Interestingly, CD4 T cells were central in facilitating this complement-mediated damage. This same C3/CD4 T cell axis triggered corneal sensory nerve damage in a mouse model of ocular graft-versus-host disease (GVHD). However, this was not the case in a T-dependent allergic eye disease (AED) model, suggesting that this inflammatory neuroimmune pathology is specific to certain disease etiologies. Collectively, these findings uncover a central role for complement in CD4 T cell-dependent corneal nerve damage in multiple disease settings and indicate the possibility for complement-targeted therapeutics to mitigate sensory neuropathies.

[Pathogenesis and epidemiology of neurotrophic keratopathy]

Neurotrophic keratopathy (NK) is a degenerative corneal disease that is based on an impairment of the corneal innervation. The damage to the sensory innervation, which is delivered through the 1st branch of the trigeminal nerve (ophthalmic nerve), can occur throughout the entire length of the nerve from the nucleus in the brainstem, e.g. caused by brain tumors, to the terminal nerve fibers in the cornea, caused for example by refractive corneal surgery (e. g. LASIK). Due to the loss of the sensory innervation, a reduced lacrimation and a reduction in the secretion of trophic factors occur. This in turn inhibits the regeneration potential of the corneal epithelium. In the most severe cases of the disease, the reduction or loss of lacrimation, together with the impaired regeneration potential of the epithelial cells, can lead to persistent epithelial defects, ulcers and corneal perforation. The NK has a prevalence of 5 or fewer individuals per 10,000 and is classified as a rare, i. e. orphan disease (ORPHA137596). A fundamental understanding of the pathogenesis and epidemiology of NK supports the early diagnosis and therefore the initiation of a specific treatment.

Corneal Sub-Basal Nerve Changes in Patients with Herpetic Keratitis During Acute Phase and after 6 Months

Background and objectives: The purpose of this study was to describe corneal sensitivity and the morphological changes of sub-basal corneal nerves using in vivo laser scanning confocal microscopy (LSCM) in herpes simplex virus (HSV) keratitis-affected eyes, and to compare with both contralateral eyes and with the eyes of patients with a previous history of herpes labialis but no history of herpetic eye disease, and with healthy patients with no history of any HSV diseases, during the acute phase of the disease and after six months. Materials and Methods: A prospective clinical study included 269 patients. All of them underwent a complete ophthalmological examination, Cochet-Bonnet aesthesiometry and LSCM within the central 5 mm of the cornea. After six months, all the patients with herpetic eye disease underwent the same examination. Serology tests of the serum to detect HSV 1/2 IgG and IgM were performed. Results: HSV-affected eyes compared with contralateral eyes, herpes labialis and healthy control group eyes demonstrated a significant decrease in corneal sensitivity, corneal nerve fibre density, corneal nerve branch density, corneal nerve fibre length and corneal nerve total branch density (p < 0.05). During follow up after six months, corneal sensitivity and sub-basal nerve parameters had increased but did not reach the parameters of contralateral eyes (p < 0.05). Previous herpes labialis did not influence corneal sensitivity and was not a risk factor for herpetic eye disease. Conclusions: Corneal sensitivity and sub-basal nerve changes in HSV-affected eyes revealed a significant decrease compared with contralateral eyes, and with the eyes of patients with a previous history of herpes labialis, and of healthy controls. Following six months, corneal sensitivity and sub-basal nerve parameters increased; however, they did not reach the parameters of contralateral eyes and the eyes of healthy controls. The best recovery of corneal sensitivity was seen in patients with epithelial keratitis. Herpes labialis was not a risk factor for herpetic eye disease.

Corneal subbasal nerve plexus changes in patients with episodic migraine: an in vivo confocal microscopy study

Background and purpose: It has been generally thought that activation and sensitization of the trigeminovascular system may contribute to the pathogenesis of migraine. Nevertheless, there is little evidence on abnormalities in peripheral trigeminal afferent nerves from humans in vivo. Alterations of corneal nerves from the ophthalmic branch of the trigeminal nerve may support the notion that trigeminal afferent nerves are involved in migraine pathophysiology. The aim of the present study was to investigate the structural changes in corneal subbasal nerve plexus in patients with episodic migraine (EM) with in vivo confocal microscope (IVCM).

Methods: In this cross-sectional observational study, 10 EM patients and 10 age- and sex-matched healthy controls were included. Analysis of IVCM images with Image J software was performed to quantify the changes in the corneal subbasal nerve plexus.

Results: EM patients showed an increase in nerve fiber length (25.0±2.65 vs 22.3±2.41 mm/mm², p=0.047) and nerve fiber density (36.3±7.29 vs 30.5±6.19 fibers/mm², p=0.104) as compared with normal controls, but this difference was not statistically significant. Nerve branching and tortuosity were significantly increased in the EM subjects compared to the normal subjects (91.3±13.8 vs 75.0±14.2 branches/mm², p=0.030 and 2.30±0.46 versus 1.63±0.52, p=0.011, respectively). In addition, nerve sprouts and increased number of Langerhans cells were observed in the EM patients.

Conclusion: The morphologic changes of corneal subbasal nerve plexus and Langerhans cell aggregation suggest the presence of nerve regeneration and inflammation in EM. Furthermore, the alterations of corneal nerves from the ophthalmic branch of the trigeminal nerve offer support for the hypothesis that the peripheral trigeminal system may be involved in the pathogenesis of migraine.

Effect of recombinant human nerve growth factor eye drops in patients with dry eye: a phase IIa, open label, multiple-dose study

BACKGROUND

Dry eye disease (DED) affects more than 14% of the elderly population causing decrease of quality of life, high costs and vision impairment. Current treatments for DED aim at lubricating and controlling inflammation of the ocular surface. Development of novel therapies targeting different pathogenic mechanisms is sought-after. The aim of this study is to evaluate safety and efficacy of recombinant human nerve growth factor (rhNGF) eye drops in patients with DED.

METHODS

Forty consecutive patients with moderate to severe DED were included in a phase IIa, prospective, open label, multiple-dose, clinical trial to receive rhNGF eye drops at 20 µg/mL (Group 1: G1) or at 4 µg/mL (Group 2: G2) concentrations, two times a day in both eyes for 28 days (NCT02101281). The primary outcomes measures were treatment-emerged adverse events (AE), Symptoms Assessment in Dry Eye (SANDE) scale, ocular surface staining and Schirmer test.

RESULTS

Of 40 included patients, 39 completed the trial. Both tested rhNGF eye drop concentrations were safe and well tolerated. Twenty-nine patients experienced at least one AE (14 in G1 and 15 in G2), of which 11 had at least 1 related AE (8 in G1 and 3 in G2). Both frequency and severity of DED symptoms and ocular surface damage showed significant improvement in both groups, while tear function improved only in G1.

CONCLUSIONS

The data of this study indicate that rhNGF eye drops in both doses is safe and effective in improving symptoms and signs of DED. Randomised clinical trials are ongoing to confirm the therapeutic benefit of rhNGF in DED.

TRIAL REGISTRATION NUMBER

NCT02101281.

Corneal confocal microscopy: ready for prime time

Corneal confocal microscopy is a non-invasive ophthalmic imaging modality, which was initially used for the diagnosis and management of corneal diseases. However, over the last 20 years it has come to the forefront as a rapid, non-invasive, reiterative, cost-effective imaging biomarker for neurodegeneration. The human cornea is endowed with the densest network of sensory unmyelinated axons, anywhere in the body. A robust body of evidence shows that corneal confocal microscopy is a reliable and reproducible method to quantify corneal nerve morphology. Changes in corneal nerve morphology precede or relate to clinical manifestations of peripheral and central neurodegenerative conditions. Moreover, in clinical intervention trials, corneal nerve regeneration occurs early and predicts functional gains in trials of neuroprotection. In view of these findings, it is timely to summarise the knowledge in this area of research and to explain why the case for corneal confocal microscopy is sufficiently compelling to argue for its inclusion as a Food and Drug Administration endpoint in clinical trials of peripheral and central neurodegenerative conditions.

Qian-Zheng-San promotes regeneration after sciatic nerve crush injury in rats

Qian-Zheng-San, a traditional Chinese prescription consisting of Typhonii Rhizoma, Bombyx Batryticatus, Scorpio, has been found to play an active therapeutic role in central nervous system diseases. However, it is unclear whether Qian-Zheng-San has therapeutic value for peripheral nerve injury. Therefore, we used Sprague-Dawley rats to investigate this. A sciatic nerve crush injury model was induced by clamping the right sciatic nerve. Subsequently, rats in the treatment group were administered 2 mL Qian-Zheng-San (1.75 g/mL) daily as systemic therapy for 1, 2, 4, or 8 weeks. Rats in the control group were not administered Qian-Zheng-San. Rats in sham group did not undergo surgery and systemic therapy. Footprint analysis was used to assess nerve motor function. Electrophysiological experiments were used to detect nerve conduction function. Immunofluorescence staining was used to assess axon counts and morphological analysis. Immunohistochemical staining was used to observe myelin regeneration of the sciatic nerve and the number of motoneurons in the anterior horn of the spinal cord. At 2 and 4 weeks postoperatively, the sciatic nerve function index, nerve conduction velocity, the number of distant regenerated axons and the axon diameter of the sciatic nerve increased in the Qian-Zheng-San treatment group compared with the control group. At 2 weeks postoperatively, nerve fiber diameter, myelin thickness, and the number of motor neurons in the lumbar spinal cord anterior horn increased in the Qian-Zheng-San treatment group compared with the control group. These results indicate that Qian-Zheng-San has a positive effect on peripheral nerve regeneration.

Persistent Corneal Epithelial Defects: A Review Article

Persistent corneal epithelial defects (PEDs or PCEDs) result from the failure of rapid re-epithelialization and closure within 10-14 days after a corneal injury, even with standard supportive treatment. Disruptions in the protective epithelial and stromal layers of the cornea can render the eye susceptible to infection, stromal ulceration, perforation, scarring, and significant vision loss. Although several therapies exist and an increasing number of novel approaches are emerging, treatment of PEDs can still be quite challenging. It is important to treat the underlying causative condition, which may include an infection, limbal stem cell deficiency, or diabetes, in order to facilitate wound healing. Standard treatments, such as bandage contact lenses (BCLs) and artificial tears (ATs), aim to provide barrier protection to the epithelial layer. Recently-developed medical treatments can target the re-epithelialization process by facilitating access to growth factors and anti-inflammatory agents, and novel surgical techniques can provide re-innervation to the cornea. PEDs should be treated within 7-10 days to avoid secondary complications. These interventions, along with a step-wise approach to management, can be useful in patients with PEDs that are refractory to standard medical treatment. In this review, we discuss the epidemiology, etiology, diagnosis, current and novel management, and prognosis of persistent epithelial defects.

Corneal re-innervation following refractive surgery treatments

Laser refractive surgery is one of the most performed surgical procedures in the world. Although regarded safe and efficient, it has side effects. All of the laser based refractive surgical procedures invoke corneal nerve injury to some degree. The impact of this denervation can range from mild discomfort to neurotrophic corneas. Currently, three techniques are widely used for laser vision correction: small incision lenticule extraction, laser-assisted keratomileusis in situ and photorefractive keratotomy. Each of these techniques affects corneal innervation differently and has a different pattern of nerve regeneration. The purpose of this review is to summarize the different underlying mechanisms for corneal nerve injury and compare the different patterns of corneal reinnervation.

Update on corneal neurotisation

Corneal neurotisation describes surgical restoration of nerve growth into the cornea to restore corneal sensation and trophic function. It represents an exciting and effective emerging treatment for neurotrophic keratopathy. Techniques described to date involve either direct nerve transfer or an interpositional nerve graft coapted to a healthy donor nerve. We review the experience to date with particular emphasis on a detailed review of techniques, outcomes and current thoughts.

Prenatal exposure to perfluorooctanoic acid induces nerve growth factor expression in cerebral cortex cells of mouse offspring

Previous studies have showed perfluorooctanoic acid (PFOA) inducing cytotoxicity in an organ. In addition, epidemiological data show that high level of PFOA in cord blood of a pregnant woman is detected. Therefore, we extrapolate that circulating PFOA may affect organogenesis in offspring, such as the brain. In this study, intrauterine exposure to PFOA in mice was used to characterize the potential impacts of prenatal PFOA exposure on cerebral cortex cells of postnatal 21 (PND21) offspring. In an ex vivo cell model, PND21-based cortex cells were exposed to PFOA or/and nerve growth factor (NGF)-specific inhibitor before further biochemical assays. As results, biochemical data showed increased trends of liver metabolic enzymes in sera of PFOA-treated PND21 mice. Interestingly, PFOA-treated PND21 mice resulted in increased levels of NGF in sera and cortex cells. In addition, PFOA-exposed cerebral cortex cells induced NGF and proliferating cell nuclear antigen (PCNA) expressions, while exposure to PFOA/NGF-specific inhibitor downregulated expressions of NGF and PCNA. In addition, Nissl-labeled, NGF-positive cells, and NGF protein expression in cortex cells of PFOA-treated PND21 mice were upregulated, respectively. Further, immunoblotting assays showed that intracephalic poly (ADP-ribose) polymerase (PARP) and p42/44 mitogen-activated protein kinase (MAPK) proliferation-regulated protein levels were elevated in PFOA-treated cortex cells. Taken together, our current findings indicate that the prenatal PFOA exposure may induce proliferation of cerebral cortex cells in PND21 mice through promoting intracephalic NGF expression in the cortex.

Developmental analysis of SV2 in the embryonic chicken corneal epithelium

Intraepithelial corneal nerves (ICNs) help protect the cornea as part of the blink reflex and by modulating tear production. ICNs are also thought to regulate the health and homeostasis of the cornea through the release of trophic factors. Disruption to these nerves can lead to vision loss. Despite their importance little is known about how corneal nerves function and even less is known about how the cornea is initially innervated during its embryonic development. Here, we investigated the innervation of the embryonic chicken cornea. Western blot and immunohistochemistry were used to characterize the localization of the synaptic vesicle marker SV2, a molecule thought to be involved in the release of trophic factors from sensory nerves. The data show that both SV2 and synaptotagmin co-localize to ICNs. Nerves in the conjunctiva also contained SV2 and synaptotagmin, but these were localized to below the basal layers of the conjunctiva epithelium. SV2 isolated from corneal epithelium migrates in western blot at a heavier weight than SV2 isolated from brain, which suggests a role in vesicle targeting, as the deglycosylating enzyme PnGase does not affect corneal SV2.

Modified insulin-like growth factor 1 containing collagen-binding domain for nerve regeneration

Insulin-like growth factor 1 (IGF-1) is a potential nutrient for nerve repair. However, it is impractical as a therapy because of its limited half-life, rapid clearance, and limited target specificity. To achieve targeted and long-lasting treatment, we investigated the addition of a binding structure by fusing a collagen-binding domain to IGF-1. After confirming its affinity for collagen, the biological activity of this construct was examined by measuring cell proliferation after transfection into PC12 and Schwann cells using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay. Immunofluorescence staining was conducted to detect neurofilament and microtubule-associated protein 2 expression, while real time-polymerase chain reaction was utilized to determine IGF-1 receptor and nerve growth factor mRNA expression. Our results demonstrate a significant increase in collagen-binding activity of the recombinant protein compared with IGF-1. Moreover, the recombinant protein promoted proliferation of PC12 and Schwann cells, and increased the expression of neurofilament and microtubule-associated protein 2. Importantly, the recombinant protein also stimulated sustained expression of IGF-1 receptor and nerve growth factor mRNA for days. These results show that the recombinant protein achieved the goal of targeting and long-lasting treatment, and thus could become a clinically used factor for promoting nerve regeneration with a prolonged therapeutic effect.