Structural effects and potential changes in growth factor signalling in penis-projecting autonomic neurons after axotomy

Mapping of functional erectogenic nerves on the rat prostate

BACKGROUND

Preservation of erectogenic nerves during radical prostatectomy (RP) is hampered by limited understanding of their precise localization, due to their complex, intertwined paths, and the inherent individual variations across patients. Because erection utilizes a subset of cavernous nerves (CNs) that in response to sexual stimuli reveal phosphorylation of neuronal nitric oxide synthase (nNOS) on its stimulatory site Ser-1412, we hypothesized that delineation of nerves containing phosphorylated (P)-nNOS on Ser-1412 would establish the location of functional erectogenic nerves within the periprostatic region.

AIM

To identify the distribution and quantity of functional erection-relevant ([P-nNOS]-containing) nerves in the periprostatic area and discriminate them among the CNs distribution. We further evaluated whether functional communication exists between contralateral CNs.

METHODS

Young adult male Sprague-Dawley rats underwent electrical stimulation of the CNs to induce penile erection via phosphorylation of nNOS on Ser-1412 (6 V for 2 min, n = 6). No stimulation group served as control (n = 6). The prostate and adjacent structures were collected and processed for whole-mount double-staining with TuJ1 antibody (a pan-axonal marker) and P-nNOS (n = 3 for stimulation, n = 3 for no stimulation), or total nNOS and P-nNOS (n = 3 for stimulation, n = 3 for no stimulation), followed by modified optical clearing and microscopic examination. Nerve quantification was done by systematic counting.

OUTCOMES

Location and quantification of functional erectogenic nerves.

RESULTS

In the male rat, we obtained a map of P-nNOS-containing nerves in the periprostatic area, which are relevant for penile erection. Only 17.5% of all nerves, and only 28.4% of the total nNOS-containing nerves in the periprostatic region are functionally erectogenic nerves. Furthermore, there is no functional innervation between contralateral (stimulated and non-stimulated) CNs.

CLINICAL IMPLICATIONS

This basic science study is expected to provide a foundation for subsequent studies at the human level. Understanding the erection-relevant nerve distribution in the periprostatic area is expected to advance nerve-sparing RP at the human level to improve sexual function outcomes.

STRENGTHS AND LIMITATIONS

This is the first study to describe and quantitate a subset of functional erection-relevant (P-nNOS-containing) nerves in the periprostatic area. Our study differs from previous studies where nerves containing total nNOS were localized without specifying which nerves produce erection. However, because this study comprised a relatively small number of rats, further studies with a bigger sample size or other model animals are warranted.

CONCLUSION

Only a subset of nerve fibers in the periprostatic region represent functional erectogenic nerves, characterized by the expression of P-nNOS (Ser-1412).

Nrf2 enhances the therapeutic efficiency of adipose-derived stem cells in the treatment of neurogenic erectile dysfunction in a rat model

BACKGROUND

Erectile dysfunction (ED) caused by intraoperative nerve injury is a major complication of pelvic surgery. Adipose-derived stem cells (ADSCs) have presented therapeutic potential in a rat model of bilateral cavernous nerve injury (BCNI), while inadequate in vivo viability has largely limited their application. Nuclear factor-E2-related Factor (Nrf2) is a key transcription factor that regulates cellular anti-oxidative stress. In this work, we investigated the effect of Nrf2 expression regulation on the viability of ADSCs, and explore its repair potential in a BCNI rat model.

RESULTS

The survival time of tert-Butylhydroquinone (tBHQ)-ADSCs in BCNI model increased obviously. In addition, the tBHQ-ADSCs group presented better restoration of major pelvic ganglion (MPG) nerve contents and fibers, better improvement of erectile function, and less penile fibrosis than the other groups. Moreover, the expression of Nrf2 and superoxide dismutase 1 (SOD1) were higher than those of other groups.

CONCLUSION

Nrf2 could enhance the anti-oxidative stress ability of ADSCs, so as to improve the therapeutic effect of ADSCs on BCNI rat model.

Implantation of skin-derived precursor Schwann cells improves erectile function in a bilateral cavernous nerve injury rat model

BACKGROUND

This study was conducted to investigate the therapeutic potential of the skin-derived precursor Schwann cells for the treatment of erectile dysfunction in a rat model of bilateral cavernous nerve injury.

RESULTS

The skin-derived precursor Schwann cells-treatment significantly restored erectile functions, accelerated the recovery of endothelial and smooth muscle tissues in the penis, and promoted nerve repair. The expression of p-Smad2/3 decreased after the treatment, which indicated significantly reduced fibrosis in the corpus cavernosum.

CONCLUSIONS

Implantation of skin-derived precursor Schwann cells is an effective therapeutic strategy for treating erectile dysfunction induced by bilateral cavernous nerve injury.

Stem Cell and Gene-Based Therapy for Erectile Dysfunction: Current Status and Future Needs

Erectile dysfunction affects an increasing number of men. The mainstays of management include oral medications, local erectogenic agents, and surgical placement of prosthetic devices. Newer technologies such as stem cell and gene therapy have been investigated as a means to restore spontaneous erectile capacity. Mesenchymal stem cells are thought to produce a local immunomodulatory and pro-repair milieu at the area of injury or needed repair. Gene therapy involves targeting the erectogenic pathway to augment factors involved in producing a natural erection. Such therapies are considered experimental and should be used in the setting of a clinical trial with appropriate oversight.

Local continuous glial cell derived neurotrophic factor release using osmotic pump promotes parasympathetic nerve rehabilitation in an animal model of cavernous nerve injury induced erectile dysfunction

Background

Nerve injury-related erectile dysfunction (ED) is one of the types that respond poorly to conventional ED treatments. Our previous experiments have demonstrated the paracrine of various neurotrophic factors (NTFs) by stem cells or other treatment modalities as a potential mechanism in the recovery of nerve injury-related ED. Glial cell derived neurotrophic factor (GDNF) is one of the essential NTFs for the regeneration of nerve fibers, especially for parasympathetic nerves. The aim of this study is to explore if local continuous GDNF administration is beneficial for the functional and histological recovery of nerve injury induced ED.

Methods

Eight-week-old male Sprague-Dawley rats were used for this study. Rats were randomly grouped into 5: Sham surgery (Sham), bilateral cavernous nerve injury (BCNI) and placebo treatment, BCNI and 0.1 µg/100 µL GDNF treatment (BCNI+GDNF 0.1), BCNI and 1 µg/100 µL GDNF treatment (BCNI+GDNF 1), BCNI and 10 µg/100 µL GDNF treatment (BCNI+GDNF 10). GDNF was administered using an osmotic pump technique which would deliver GDNF locally and continuously for 28 days without the need for external connections or frequent handling of animals. Recovery of sexual function, nerve fibers regeneration, and expression of neurotrophic receptors were examined and compared among groups after the treatment.

Results

Local continuous GDNF release treatment increased the average number of intromissions in the sexual behavior test and intracavernous pressure (ICP) in the erectile function test in a dose dependent manner. Osmotic pump implantation induced increased local GDNF concentration and mild inflammatory response. Gene expression of GDNF receptors in major pelvic ganglion (MPG) and nerve regeneration along the urethra were partially promoted by GDNF. These changes were associated with increased nerve fibers especially the parasympathetic nerve fibers in dorsal nerve of penis (DNP) in GDNF treated groups.

Conclusions

In conclusion, our project illustrated the promising effects of local continuous GDNF administration for the functional and histological recovery of nerve injury-induced ED.

Co-overexpression of VEGF and GDNF in adipose-derived stem cells optimizes therapeutic effect in neurogenic erectile dysfunction model

Objectives

To evaluate the rapid repair potential of adipose‐derived stem cells (ADSCs) co‐overexpressing VEGF and GDNF on bilateral cavernous nerve injury (BCNI) in rat models. Progressive fibrosis of the penis that occurs shortly after BCNI is a key cause of clinical treatment difficulty of erectile dysfunction (ED). Traditional medications are ineffective for ED caused by BCNI. ADSCs have shown therapeutic effects in animal models, but disappointing in clinical treatment suggests that we should explore optimal treatment of it.

Materials and methods

We extracted ADSCs from rat epididymis. Lentiviral transfection was verified by western blot and immunofluorescence. Thirty‐six SD rats (10 weeks old) were randomly divided into six groups (n = 6 per group): sham surgery, and remaining five BCNI groups transplanted PBS or ADSCs which were genetically modified by vehicle, VEGF (ADSC‐V), GDNF (ADSC‐G), or VEGF&GDNF (ADSC‐G&V) around major pelvic ganglion (MPG). We investigated the therapeutic effects of BCNI rat model which is characterized by ED, penile tissue fibrosis and hypoxia, and lack of nitrogen nerves or vascular atrophy.

Results

Erectile function was almost recovered after 2 weeks of transplantation of ADSC‐G&V, promoted cavernous nerve repair, prevented penile fibrosis and preserving the vascular endothelium, which was significant differences amongst ADSC‐V or ADSC‐G. Moreover, GM‐ADSCs were detected in MPG and penis, indicating that their participation in repair of target organs and transverse nerves.

Conclusions

These promising data indicate that ADSCs co‐overexpressed VEGF and GDNF‐induced synergistic effects, make it a potential tool for recovering of erectile function speedily after BCNI.

Recovery of erectile function comparing autologous nerve grafts, unseeded conduits, Schwann-cell-seeded guidance tubes and GDNF-overexpressing Schwann cell grafts

Dissection of the cavernous nerves during radical prostatectomy for prostate cancer eliminates spontaneous erections. Using the rat as an experimental model, we compared the regenerative capacity of autologous nerve grafts and Schwann-cell-seeded nerve guides. After bilateral excision of cavernous nerve segments, cavernous nerves were reconstructed using unseeded silicon tubes, nerve autografts and silicon tubes seeded with either Glial-cell-line-derived (GDNF)-overexpressing or green fluorescent protein (GFP)-expressing Schwann cells (SCs) (16 study nerves per group). Control groups underwent either a sham operation or bilateral excision of cavernous nerve segments without repair. After 12 weeks erectile function was assessed by neurostimulation and intracavernous pressure (ICP) measurement. The reconstructed nerve segments were excised and histologically analyzed. We demonstrated an intact erectile response upon neurostimulation in 25% (4/16) of autologous nerve grafts, in 50% (8/16) of unseeded tubes, in 75% (12/16) of the Schwann-cell-GFP group and in 93.75% (15/16) of the GDNF group. ICP was significantly increased when comparing the Schwann-cell-GFP group with nerve autografts, unseeded conduits and negative controls (P<0.005). In conclusion, Schwann-cell-seeded scaffolds combined with neurotrophic factors are superior to unseeded tubes and autologous nerve grafts. They present a promising therapeutic approach for the repair of erectile nerve gaps.

Peptide amphiphile nanofiber hydrogel delivery of sonic hedgehog protein to the cavernous nerve to promote regeneration and prevent erectile dysfunction

Erectile dysfunction (ED) has high impact on quality of life in prostatectomy, diabetic and aging patients. An underlying mechanism is cavernous nerve (CN) injury, which causes ED in up to 80% of prostatectomy patients. We examine how sonic hedgehog (SHH) treatment with innovative peptide amphiphile nanofiber hydrogels (PA), promotes CN regeneration after injury. SHH and its receptors patched (PTCH1) and smoothened (SMO) are localized in PG neurons and glia. SMO undergoes anterograde transport to signal to downstream targets. With crush injury, PG neurons degenerate and undergo apoptosis. SHH protein decreases, SMO localization changes to the neuronal cell surface, and anterograde transport stops. With SHH treatment SHH is taken up at the injury site and undergoes retrograde transport to PG neurons, allowing SMO transport to occur, and neurons remain intact. SHH treatment prevents neuronal degeneration, maintains neuronal, glial and downstream target signaling, and is significant as a regenerative therapy.

Pioglitazone Enhances Survival and Regeneration of Pelvic Ganglion Neurons After Cavernosal Nerve Injury

OBJECTIVE

To investigate the effects of pioglitazone on pelvic ganglion neurons in a rat model of bilateral cavernosal nerve crush injury (BCNI), thereby elucidating the actions of pioglitazone in preventing post-prostatectomy neurogenic erectile dysfunction.

METHODS

Sprague-Dawley rats aged 12 weeks were divided into four groups: (a) sham procedure, (b) BCNI, (c) BCNI + postsurgical pioglitazone, and (d) BCNI + pre and postsurgical pioglitazone (preventive therapy). Preoperative injection of Fluoro-Gold (FG) fluorescent tracer into the cavernosal tissue was performed for retrograde labeling of pelvic ganglion cells. Pelvic ganglia were resected at 2 weeks in all rats and processed for real-time polymerase chain reaction, immunohistochemistry, and Western blot to examine the expression of FG, neuronal nitric oxide synthase, β-III tubulin, neurturin, and glial cell line-derived neurotrophic factor family receptor alpha-2 (GFRα2).

RESULTS

Animals treated with pre- and postsurgical pioglitazone demonstrated increased staining for FG similar to sham levels. Gene expression of neuronal nitric oxide synthase, neurturin, GFRα2, and β-III tubulin was also upregulated in the group receiving preventive therapy.

CONCLUSION

Pioglitazone provides a protective effect on pelvic ganglion neurons after BCNI.

Developing a functional urinary bladder: a neuronal context

The development of organs occurs in parallel with the formation of their nerve supply. The innervation of pelvic organs (lower urinary tract, hindgut, and sexual organs) is complex and we know remarkably little about the mechanisms that form these neural pathways. The goal of this short review is to use the urinary bladder as an example to stimulate interest in this question. The bladder requires a healthy mature nervous system to store urine and release it at behaviorally appropriate times. Understanding the mechanisms underlying the construction of these neural circuits is not only relevant to defining the basis of developmental problems but may also suggest strategies to restore connectivity and function following injury or disease in adults. The bladder nerve supply comprises multiple classes of sensory, and parasympathetic or sympathetic autonomic effector (motor) neurons. First, we define the developmental endpoint by describing this circuitry in adult rodents. Next we discuss the innervation of the developing bladder, identifying challenges posed by this area of research. Last we provide examples of genetically modified mice with bladder dysfunction and suggest potential neural contributors to this state.

Animal models of erectile dysfunction

Erectile dysfunction (ED) is a prevalent male sexual dysfunction with profound adverse effects on the physical and the psychosocial health of men and, subsequently, on their partners. The expanded use of various types of rodent models has produced some advances in the study of ED, and neurophysiological studies using various animal models have provided important insights into human sexual dysfunction. At present, animal models play a key role in exploring and screening novel drugs designed to treat ED.

Temporal changes in neurotrophic factors and neurite outgrowth in the major pelvic ganglion following cavernous nerve injury

Despite nerve-sparing radical prostatectomy, nerve damage and erectile dysfunction (ED) prevail, and preventing neurodegeneration is of great importance. Neurotrophic factors and neurite outgrowth were characterized in major pelvic ganglia (MPG) following bilateral cavernous nerve injury (BCNI). Young male Sprague-Dawley rats underwent sham or BCNI surgery, and the intracavernosal pressure to mean arterial pressure ratio was measured 2, 7, 14, 21, 30, and 60 days following injury (n = 8/group). MPG gene expression (qPCR) and Western blot were performed for glial cell line-derived neurotrophic factor (GDNF), nerve growth factor (NGF), neurturin, neurotrophin (NT)-3, NT4, brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor, and activating transcription factor 3 (ATF3). Additional rats were injured, and MPGs were removed 24 hr, 48 hr, 3 days, and 7 days following BCNI (n = 3/group). MPGs were cultured in Matrigel, and neurite outgrowth was measured. Erections were impaired early and improved by 60 days in BCNI rats. GDNF, NGF, BDNF, and ATF3 gene expression was significantly increased and NT3 was decreased in MPGs following BCNI (48 hr to 21 days, P < 0.05). GDNF and NGF protein levels were elevated in 48-hr BCNI rats. MPG neurite outgrowth from 24-hr and 48-hr BCNI was higher than sham (658 ± 19 μm, 607 ± 24 μm, 393 ± 23 μm, respectively, P < 0.05). Further studies examining the roles of neurotrophic factors in modulating signaling pathways may provide therapeutic avenues for neurogenically mediated ED.

Decrease in neuronal nicotinic acetylcholine receptor subunit and PSD-93 transcript levels in the male mouse MPG after cavernous nerve injury or explant culture

Quantitative real-time PCR was used to test whether cavernous nerve injury leads to a decrease in major pelvic ganglia (MPG) neuronal nicotinic ACh receptor (nAChR) subunit and postsynaptic density (PSD)-93 transcript levels. Subunits α3, β4, and α7, commonly expressed in the MPG, were selected for analysis. After 72 h in explant culture, MPG transcript levels for α3, β4, α7, and PSD-93 were significantly depressed. Three days after cavernous nerve axotomy or crush in vivo, transcript levels for α3, β4, and PSD-93, but not for α7, were significantly depressed. Three days after dissection of the cavernous nerve free of underlying tissue and application of a 5-mm lateral stretch (manipulation), transcript levels for α3 and PSD-93 were also significantly decreased. Seven days after all three surgical procedures, α3 transcript levels remained depressed, but PSD-93 transcript levels were still decreased only after axotomy or nerve crush. At 30 days postsurgery, transcript levels for the nAChR subunits and PSD-93 had recovered. ACh-induced currents were significantly smaller in MPG neurons dissociated from 3-day explant cultured ganglia than from those recorded in neurons dissociated from acutely isolated ganglia; this observation provides direct evidence showing that a decrease in nAChR function was coincident with a decrease in nAChR subunit transcript levels. We conclude that a downregulation of nAChR subunit and PSD-93 expression after cavernous nerve injury, or even manipulation, could interrupt synaptic transmission within the MPG and thus contribute to the loss of neural control of urogenital organs after pelvic surgeries.

Effect of mesenchymal stem cells associated to matrixen on the erectile function in the rat model with bilateral cavernous nerve crushing injury

OBJECTIVES

To evaluate the effect of mesenchymal stem cells (MSCs) and MSCs mixed with Matrixen as a cell carrier on the erectile dysfunction caused by bilateral cavernous nerve crushing injury.

MATERIALS AND METHODS

White male Sprague-Dawley rats were divided into 4 groups: sham-operated control group (n = 5), bilateral cavernous nerve crushing group (BCNC group, n = 10), BCNC administered with MSCs group (n = 10,1x106 in 20 µL), BCNC administered with Matrixen group (n = 10.1x106 in 20 µL), BCNC administered with MSCs/Matrixen group (n = 10.1x106 in 20 µL). After functional assessment at 4 weeks, major pelvic ganglion (MPG) and penile tissue were collected. Immunofluorescent staining of MPG was performed with PKH26 and Tuj1. Western blot analysis of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) were done in corpus cavernosum.

RESULTS

ICP/MAP ratios of BCNC with MSCs and MSCs/Matrixen groups were significantly increased compared with BCNC and BCNC with Matrixen group. Moreover, ICP/MAP ratios of MSCs/Matrixen group were significantly increased compared with BCNC with MSCs group. In MPG, the more implantation of MSCs and increased expression of nerve cells were observed in MSCs/Matrixen group compared with BCNC with MSCs group. Significant increase expression of eNOS and nNOS was also noted in BCNC with MSCs/Matrixen group.

CONCLUSION

The erectile function was more preserved in MSCs/Matrixen group compared with the administration of MSCs alone in the rats with bilateral cavernous nerve crushing injury. Therefore, we consider that the use of transplant cell carrier such as Matrixen may help the implantation of MSCs and improve the therapeutic effect of MSCs.

Sildenafil promotes neuroprotection of the pelvic ganglia neurones after bilateral cavernosal nerve resection in the rat

OBJECTIVE

To determine the gene expression profile of pelvic ganglia neurones after bilateral cavernosal nerve resection (BCNR) and subsequent treatment with sildenafil in relation to neurotrophic-related pathways.

MATERIALS AND METHODS

Fisher rats aged 5 months were subjected to BCNR or sham operation and treated with or without sildenafil (20 mg/kg body-weight in drinking water) for 7 days. Total RNA isolated from pelvic ganglia was subjected to reverse transcription and then to quantitative reverse transcriptase-polymerase chain reaction (PCR) with the RAT-neurotrophic array. Results were corroborated by real-time PCR and western blotting. Another set of animals were injected with a fluorescent tracer at the base of the penis, 7 days before BCNR or sham operation, and were sacrificed 7 days after surgery. Sections of pelvic ganglia were used for immunohistochemistry with antibodies against neurturin, neuronal nitric oxide synthase, tyrosine hydroxylase and glial cell line-derived neurotrophic factor receptor α2.

RESULTS

A down-regulation of the expression of neuronal nitric oxide synthase accompanied by changes in the level of cholinergic neurotrophic factors, such as neurturin and its receptor glial cell line-derived neurotrophic factor receptor α2, artemin, neurotrophin-4 and cilliary neurotrophic factor, was observed 7 days after BCNR in pelvic ganglia neurones. Treatment with sildenafil, starting immediately after surgery, reversed all these changes at a level similar to that in sham-operated animals.

CONCLUSIONS

Sildenafil treatment promotes changes in the neurotrophic phenotype, leading to a regenerative state of pelvic ganglia neurones. The present study provides a justification for the use of phosphodiesterase 5 inhibitors as a neuroprotective agent after BCNR.

Semaphorin 3A inhibits growth of adult sympathetic and parasympathetic neurones via distinct cyclic nucleotide signalling pathways

BACKGROUND AND PURPOSE

Semaphorin 3A (Sema3A) is an important secreted repulsive guidance factor for many developing neurones. Sema3A continues to be expressed in adulthood, and expression of its receptor, neuropilin-1 (Nrp-1), can be altered by nerve injury. Autonomic neurones innervating the pelvic viscera are particularly susceptible to damage during pelvic surgical procedures, and failure to regenerate or aberrant growth of sympathetic and parasympathetic nerves lead to organ dysfunction. However, it is not known if adult pelvic neurones are potential targets for Sema3A.

EXPERIMENTAL APPROACH

The effects of Sema3A and activation or inhibition of cyclic nucleotide signalling were assessed in adult rat pelvic ganglion neurones in culture using a growth cone collapse assay.

KEY RESULTS

Sema3A caused growth cone collapse in both parasympathetic and sympathetic neurones expressing Nrp-1. However, the effect of Sema3A was mediated by distinct cyclic nucleotide signalling pathways in each neurone type. In parasympathetic neurones, cAMP and downstream activation of protein kinase A were required for growth cone collapse. In sympathetic neurones, cGMP was required for Sema3A-induced collapse; cAMP can also cause collapse but was not required. Sema3A-mediated, cGMP-dependent collapse in sympathetic neurones may require activation of cyclic nucleotide-gated ion channels (CNGCs).

CONCLUSIONS AND IMPLICATIONS

We propose that Sema3A is an important guidance factor for adult pelvic autonomic neurones, and that manipulation of their distinct signalling mechanisms could potentially promote functional selective regeneration or attenuate aberrant growth. To our knowledge, this is also the first study to implicate CNGCs in regulating growth cone dynamics of adult neurones.

Gene therapy as future treatment of erectile dysfunction

IMPORTANCE OF THE FIELD

Erectile dysfunction (ED) is a major men's health problem. Although the high success rate of treating ED by phosphodiesterase 5 (PDE5) inhibitors has been reported, there are a significant number of ED patients who do not respond to currently available treatment modalities.

AREAS COVERED IN THIS REVIEW

To elucidate the current status of gene therapy applications for ED, gene therapy approaches for ED treatment are reviewed.

WHAT THE READER WILL GAIN

Gene therapy strategies that can enhance nitric oxide (NO) production or NO-mediated signaling pathways, growth factor-mediated nerve regeneration or K(+) channel activity in the smooth muscle could be promising approaches for the treatment of ED. Although the majority of gene therapy studies are still in the preclinical phase, the first clinical trial using non-viral gene transfer of Ca(2+)-activated, large-conductance K(+) channels into the corpus cavernosum of ED patients showed positive results.

TAKE HOME MESSAGE

Gene therapy represents an exciting future treatment option for ED, especially for people with severe ED unresponsive to current first-line therapies such as PDE5 inhibitors although the long-term safety of both viral and non-viral gene therapies should be established.

Development of the autonomic nervous system: a comparative view

In this review we summarize current understanding of the development of autonomic neurons in vertebrates. The mechanisms controlling the development of sympathetic and enteric neurons have been studied in considerable detail in laboratory mammals, chick and zebrafish, and there are also limited data about the development of sympathetic and enteric neurons in amphibians. Little is known about the development of parasympathetic neurons apart from the ciliary ganglion in chicks. Although there are considerable gaps in our knowledge, some of the mechanisms controlling sympathetic and enteric neuron development appear to be conserved between mammals, avians and zebrafish. For example, some of the transcriptional regulators involved in the development of sympathetic neurons are conserved between mammals, avians and zebrafish, and the requirement for Ret signalling in the development of enteric neurons is conserved between mammals (including humans), avians and zebrafish. However, there are also differences between species in the migratory pathways followed by sympathetic and enteric neuron precursors and in the requirements for some signalling pathways.

Emerging gene and stem cell therapies for the treatment of erectile dysfunction

Erectile dysfunction is a prevalent condition that leads to significant morbidity and distress, not just for affected men but also for their partners. Very few currently available treatments ameliorate the underlying causes of the disorder and 'cure' the disease state. Much recent effort has been focused on the development of gene and cell-based approaches to rectify the molecular and tissue defects responsible for ED. Gene therapy has been investigated in animal models as a means to restore normal function to the penis; at this time, however, only one human trial has been published in the peer-reviewed literature. Recent gene therapy studies have focused on the modulation of enzymes associated with the NOS/cGMP pathway, and supplementation of trophic factors, peptides and potassium channels. Stem cell therapy has been a topic of interest in more recent years but there are currently very few published reports in animal models and none in human men. Although stem cell therapy offers the potential for restoration of functional tissues, legitimate concerns remain regarding the long-term fate of stem cells. The long-term safety of both gene and stem cell therapy must be thoroughly investigated before large-scale human studies can be considered.

Nerve growth factor modulation of the cavernous nerve response to injury

INTRODUCTION

Surgical therapies for prostate cancer and other pelvic malignancies often result in neuronal damage and debilitating loss of sexual function due to cavernous nerve (CN) trauma. Advances in the neurobiology of growth factors have heightened clinical interest in the development of protective and regenerative neuromodulatory strategies targeting CN recovery following injury.

AIM

The aim of this review was to offer an examination of current and future nerve growth factor (NGF) modulation of the CN response to injury with a focus on brain-derived nerve growth factor (BDNF), growth differentiation factor-5 (GDF-5), and neurturin (NTN).

METHODS

Information for this presentation was derived from a current literature search using the National Library of Medicine PubMed Services producing publications relevant to this topic. Search terms included neuroprotection, nerve regeneration, NGFs, neurotrophic factors, BDNF, GDF-5, NTN, and CNs.

MAIN OUTCOME MEASURES

Basic science studies satisfying the search inclusion criteria were reviewed.

RESULTS

In this session, BDNF, atypical growth factors GDF-5 and NTN, and their potential influence upon CN recovery after injury are reviewed, as are the molecular pathways by which their influence is exerted.

CONCLUSIONS

Compromised CN function is a significant cause of erectile dysfunction development following prostatectomy and serves as the primary target for potential neuroprotective or regenerative strategies utilizing NGFs such as BDNF, GDF-5, and NTN, and/or targeted novel therapeutics modulating signaling pathways.

Herpes simplex virus vector-mediated delivery of neurturin rescues erectile dysfunction of cavernous nerve injury

Neurturin (NTN), a member of glial cell line-derived neurotrophic factor (GDNF) family, is known as an important neurotrophic factor for penis-projecting neurons. We recently demonstrated significant protection from erectile dysfunction (ED) following a replication-defective herpes simplex virus (HSV) vector-mediated GDNF delivery to the injured cavernous nerve. Herein, we applied HSV vector-mediated delivery of NTN to this ED model. Rat cavernous nerve was injured bilaterally using a clamp and dry ice. For HSV-treated groups, 20 microl of vector stock was administered directly to the damaged nerve. Delivery of an HSV vector expressing both green fluorescent protein and lacZ (HSV-LacZ) was used as a control. Intracavernous pressure along with systemic arterial pressure (ICP/AP) was measured 2 and 4 weeks after the nerve injury. Fluorogold (FG) was injected into the penile crus 7 days before being killed to assess neuronal survival. Four weeks after nerve injury, rats treated with HSV-NTN exhibited significantly higher ICP/AP compared with untreated or control vector-treated groups. The HSV-NTN group had more FG-positive major pelvic ganglion neurons than the control group following injury. HSV vector-mediated delivery of NTN could be a viable approach for the improvement of ED following cavernous nerve injury.

Alteration of glial cell line-derived neurotrophic factor family receptor alpha-2 mRNA expression and its co-expression with neuronal nitric oxide synthase in pelvic ganglia following unilateral cavernous nerve injury

OBJECTIVES

The goal of this study was to determine the alterations of glial cell line-derived neurotrophic factor family receptor alpha-2 (GFRalpha2) mRNA expression in the major pelvic ganglia (MPG) and their relationship to the marker for the neural plasticity (growth-associated protein 43: GAP-43) and neuronal nitric oxide synthase (nNOS)-positive neurons following cavernous nerve injury.

METHODS

Cavernous nerves were transected unilaterally in 24 Sprague-Dawley rats aged 8 weeks. We used nine sham operated same animals as controls. Bilateral MPGs were harvested at 1, 3, and 6 months following nerve injury. The GFRalpha2 and GAP-43 mRNA expressions of the sham group and the injury group (3 months after surgery) were investigated by reverse transcription-polymerase chain reaction. We also investigated the expression profile of GFRalpha2 mRNA by in situ hybridization combined with nNOS immunostaining.

RESULTS

It was revealed semi-quantitatively that the GAP43 mRNA expression moderately increased in the intact MPG, and GFRalpha2 mRNA was maintained in the intact MPG but not in the injured one. A histological double-labeling study showed that the number of GFRalpha2 mRNA- and nNOS-positive neurons increased in the intact MPG and most GFRalpha2 mRNA expressions were colocalized with nNOS immunostaining.

CONCLUSIONS

The current study suggested that the GFRalpha2 mRNA alteration closely related to the nNOS expression following the cavernous nerve injury, which would be involved in the maintenance and recovery of erectile function.

Emerging neuromodulatory molecules for the treatment of neurogenic erectile dysfunction caused by cavernous nerve injury

Advances in the neurobiology of growth factors, neural development, and prevention of cell death have resulted in a heightened clinical interest for the development of protective and regenerative neuromodulatory strategies for the cavernous nerves (CNs), as therapies for prostate cancer and other pelvic malignancies often result in neuronal damage and debilitating loss of sexual function. Nitric oxide released from the axonal end plates of these nerves within the corpora cavernosa causes relaxation of smooth muscle, initiating the haemodynamic changes of penile erection as well as contributing to maintained tumescence; the loss of CN function is primarily responsible for the development of erectile dysfunction (ED) after pelvic surgery and serves as the primary target for potential neuroprotective or regenerative strategies. Evidence from pre-clinical studies for select neuromodulatory approaches is reviewed, including neurotrophins, glial cell line-derived neurotrophic factors (GDNF), bone morphogenic proteins, immunophilin ligands, erythropoetin (EPO), and stem cells.

Neurturin regulates postnatal differentiation of parasympathetic pelvic ganglion neurons, initial axonal projections, and maintenance of terminal fields in male urogenital organs

We have investigated the development of autonomic nerves in the urogenital tract of male mice and the effect of neurturin gene deletion on this process. At birth, autonomic innervation of the reproductive organs was sparse, but urinary bladder smooth muscle was well innervated. Further innervation of reproductive tissues occurred until P21, but noradrenergic axons established their complete terminal field later than nitrergic cholinergic axons: in adults the former are more prevalent, yet this became apparent only at P7 (vas deferens, seminal vesicles), P14 (prostate) or after P14 (penis). Neurturin was essential for initial projection of axons (mucosa of vas deferens), maintenance of terminal fields (prostate and seminal vesicles), or both functions (cavernosum of penis). In contrast, some targets (e.g., bladder muscle and suburothelium, vas deferens smooth muscle) were unaffected by neurturin gene deletion. Pelvic ganglion neurons more than doubled between birth and adulthood, probably as aresult of continued maturation of p75-positive undifferentiated neuronal precursors rather than cell division. The adult number of neurons was achieved by P7 (sympathetic) or P21 (parasympathetic). In adult neurturin knockout mice, there were approximately 25% fewer parasympathetic neurons compared with wild types, because of failure of differentiation after P14. This study revealed the complexity of postnatal maturation of urogenital innervation, with each organ showing a distinct chronology of innervation and different requirement for neurturin. Our results also indicate that in adults there will be distinct differences in neurturin dependence between organs, such that proregenerative therapies may have to be tailored specifically for the nerve pathway of interest.

Herpes simplex virus vector-mediated delivery of glial cell line-derived neurotrophic factor rescues erectile dysfunction following cavernous nerve injury

Erectile dysfunction (ED) is frequently associated with injury to the cavernous nerve sustained during pelvic surgery. Functional recovery from cavernous nerve injury is generally incomplete and occurs over an extended time frame. We employed a therapeutic gene transfer approach with herpes simplex virus (HSV) vector expressing glial cell line-derived neurotrophic factor (GDNF). Rat cavernous nerve was injured bilaterally using a clamp and dry ice. For HSV-treated groups, 20 microl of purified vector stock was administered directly to and around the damaged nerve. Delivery of an HSV vector expressing both green fluorescent protein (GFP) and lacZ (HSV-LacZ) was used as a control. Intracavernous pressure along with systemic arterial pressure (ICP/AP) was measured 2 and 4 weeks after the nerve injury. Fluorogold (FG) was injected into the penile crus 7 days before killing to assess nerve survival. Approximately 60% of major pelvic ganglion (MPG) cells were GFP positive after viral administration. At 4 weeks after nerve injury, rats treated with HSV-GDNF exhibited significant recovery of ICP/AP compared with control vector or untreated groups. The HSV-GDNF group also yielded more FG-positive MPG cells than the control vector group. HSV vector-mediated delivery of GDNF presents a viable approach for the treatment of ED following cavernous nerve injury.

Neurturin enhances the recovery of erectile function following bilateral cavernous nerve crush injury in the rat

Background

The molecular mechanisms responsible for the survival and preservation of function for adult parasympathetic ganglion neurons following injury remain incompletely understood. However, advances in the neurobiology of growth factors, neural development, and prevention of cell death have led to a surge of clinical interest for protective and regenerative neuromodulatory strategies, as surgical therapies for prostate, bladder, and colorectal cancers often result in neuronal axotomy and debilitating loss of sexual function or continence. In vitro studies have identified neurturin, a glial cell line-derived neurotrophic factor, as a neuromodulator for pelvic cholinergic neurons. We present the first in vivo report of the effects of neurturin upon the recovery of erectile function following bilateral cavernous nerve crush injury in the rat.

Methods

In these experiments, groups (n = 8 each) consisted of uninjured controls and animals treated with injection of albumin (blinded crush control group), extended release neurotrophin-4 or neurturin to the site of cavernous nerve crush injury (100 μg per animal). After 5 weeks, recovery of erectile function (treatment effect) was assessed by cavernous nerve electrostimulation and peak aortic pressures were measured. Investigators were unblinded to specific treatments after statistical analyses were completed.

Results

Erectile dysfunction was not observed in the sham group (mean maximal intracavernous pressure [ICP] increase of 117.5 ± 7.3 cmH₂O), whereas nerve injury and albumin treatment (control) produced a significant reduction in ICP elevation of 40.0 ± 6.3 cmH₂O. Neurturin facilitated the preservation of erectile function, with an ICP increase of 55% at 62.0 ± 9.2 cmH₂O (p < 0.05 vs control). Extended release neurotrophin-4 did not significantly enhance recovery of erectile function with an ICP change of 46.9 ± 9.6. Peak aortic blood pressures did not differ between groups. No significant pre- and post-treatment weight differences were observed between control, neurotrophin-4 and neurturin cohorts. All animals tolerated the five-week treatment course.

Conclusion

Treatment with neurturin at the site of cavernous nerve crush injury facilitates recovery of erectile function. Results support further investigation of neurturin as a neuroprotective and/or neuroregenerative agent facilitating functional recovery after cavernous or other pelvic autonomic nerve injuries.

FK1706 Enhances the Recovery of Erectile Function Following Bilateral Cavernous Nerve Crush Injury in the Rat

INTRODUCTION

Advances in neurobiology have led to a surge of clinical interest in the development of protective and regenerative neuromodulatory strategies, as surgical therapies for prostate cancer often result in neuronal damage and debilitating loss of sexual function.

AIM

To investigate the dose-dependent efficacy of FK1706, a nonimmunosuppressant immunophilin ligand, for the recovery of erectile function following bilateral cavernous nerve crush injury in the rat.

MAIN OUTCOME MEASURES

Recovery of erectile function was assessed by cavernous nerve electrostimulation and reported as maximal increase of intracavernous pressure (ICP) and area under the curve (AUC). Changes in animal weights, percentage completion of treatment course, and survival were compared between groups. METHODS; Thirty-five Sprague-Dawley male rats were randomly divided into five equal groups: seven animals received a sham operation, whereas 28 animals underwent bilateral cavernous nerve crush injury, followed by subcutaneous injection of vehicle alone (1.0 mL/kg), or low (0.1 mg/kg), medium (0.32 mg/kg), or high dose (1.0 mg/kg) FK1706 5 days per week for 8 weeks.

RESULTS

Erectile dysfunction did not occur in the sham group (mean maximal ICP increase of 100.8 +/- 6.3 cmH(2)O), whereas nerve injury and vehicle treatment produced a significant reduction in ICP response to 34.4 +/- 12.8 cmH(2)O. The mean ICP increase for high-dose FK106 treatment was 73.9 +/- 6.3 cmH(2)O (P < 0.01 vs. vehicle) compared with 58.3 +/- 7.4 cmH(2)O and 56.9 +/- 8.3 for low and medium doses (P > 0.05). Similar stepwise findings were observed using AUC data. No significant maximal aortic blood pressure or weight differences occurred between groups and all animals completed treatment.

CONCLUSION

High-dose subcutaneous FK1706 therapy promoted recovery of erectile function following bilateral cavernous nerve crush injury in the rat. No significant differences between groups were observed for changes in weight, and the 8-week treatment course was completed for all animals.