Death of injured neurons caused by the precursor of nerve growth factor

Neutralizing antibody to proNGF rescues erectile function by regulating the expression of neurotrophic and angiogenic factors in a mouse model of cavernous nerve injury

BACKGROUND

Radical prostatectomy induces some degree of cavernous nerve injury (CNI) and causes denervation-induced pathologic changes in cavernous vasculature, regardless of the advances in surgical techniques and robotic procedures. The precursor for nerve growth factor (proNGF) is known to be involved in neuronal cell apoptosis and microvascular dysfunction through its receptor p75NTR .

OBJECTIVES

To determine the expression of proNGF/p75NTR and the efficacy of proNGF neutralizing antibody (anti-proNGF-Ab) in a mouse model of ED induced by CNI.

MATERIALS AND METHODS

Age-matched 12-week-old C57BL/6 mice were distributed into three groups: sham group and bilateral CNI group treated with intracavernous injections of PBS (20 μL) or of anti-proNGF-Ab (20 µg in 20 μL of PBS) on days -3 and 0. Two weeks after treatment, erectile function was measured by electrical stimulation of cavernous nerve. Penis tissues from a separate group of animals were harvested for further analysis. We also determined the efficacy of anti-proNGF-Ab on neural preservation in major pelvic ganglion (MPG) ex vivo.

RESULTS

We observed increased penile expression of proNGF and p75NTR after CNI. Intracavernous administration of anti-proNGF-Ab increased nNOS and neurofilament expression probably by enhancing the production of neurotrophic factors, such as neurotrophin-3, NGF, and brain-derived neurotrophic factor. Anti-proNGF-Ab preserved the integrity of cavernous sinusoids, such as pericytes, endothelial cells, and endothelial cell-to-cell junctions, possibly by controlling angiogenic factors (angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor) and induced endogenous eNOS phosphorylation in CNI mice. And finally, treatment with anti-proNGF-Ab rescued erectile function in CNI mice. Anti-proNGF-Ab also enhanced neurite sprouting from MPG exposed to lipopolysaccharide.

DISCUSSION AND CONCLUSION

The preservation of damaged cavernous neurovasculature through inhibition of the proNGF/p75NTR pathway may be a novel strategy to treat radical prostatectomy-induced erectile dysfunction.

Oral Administration of the p75 Neurotrophin Receptor Modulator, LM11A-31, Improves Erectile Function in a Mouse Model of Cavernous Nerve Injury

BACKGROUND

Radical prostatectomy for prostate cancer can not only induce cavernous nerve injury (CNI), but also causes cavernous hypoxia and cavernous structural changes, which lead to a poor response to phosphodiesterase 5 inhibitors.

AIM

To investigate the therapeutic effect of oral administration of LM11A-31, a small molecule p75 neurotrophin receptor (p75^NTR) ligand and proNGF antagonist, in a mouse model of bilateral CNI, which mimics nerve injury-induced erectile dysfunction after radical prostatectomy.

METHODS

8-week-old male C57BL/6 mice were divided into sham operation and CNI groups. Each group was divided into 2 subgroups: phosphate-buffered saline and LM11A-31 (50 mg/kg/day) being administered once daily starting 3 days before CNI via oral gavage. 2 weeks after CNI, we measured erectile function by electrical stimulation of the bilateral cavernous nerve. The penis was harvested for histologic examination and Western blot analysis. The major pelvic ganglia was harvested and cultured for assays of ex vivo neurite outgrowth.

OUTCOMES

Intracavernous pressure, neurovascular regeneration in the penis, in vivo or ex vivo functional evaluation, and cell survival signaling were measured.

RESULTS

Erectile function was decreased in the CNI group (44% of the sham operation group), while administration of LM11A-31 led to a significant improvement of erectile function (70% of the sham operation group) in association with increased neurovascular content, including cavernous endothelial cells, pericytes, and neuronal processes. Immunohistochemical and Western blot analyses showed significantly increased p75^NTR expression in the dorsal nerve of CNI mice, which was attenuated by LM11A-31 treatment. Protein expression of active PI3K, AKT, and endothelial nitric oxide synthase was increased, and cell death and c-Jun N-terminal kinase signaling was significantly attenuated after LM11A-31 treatment. Furthermore, LM11A-31 promoted neurite sprouting in cultured major pelvic ganglia after lipopolysaccharide exposure.

CLINICAL IMPLICATIONS

LM11A-31 may be used as a strategy to treat erectile dysfunction after radical prostatectomy or in men with neurovascular diseases.

STRENGTHS & LIMITATIONS

Unlike biological therapeutics, such as proteins, gene therapies, or stem cells, the clinical application of LM11A-31 would likely be relatively less complex and low cost. Our study has some limitations. Future studies will assess the optimal dosing and duration of the compound. Given its plasma half-life of approximately 1 hour, it is possible that dosing more than once per day will provide added efficacy.

CONCLUSION

Specific inhibition of the proNGF-p75^NTR degenerative signaling via oral administration of LM11A-31 represents a novel therapeutic strategy for erectile dysfunction induced by nerve injury. Yin GN, Ock J, Limanjaya A, et al. Oral Administration of the p75 Neurotrophin Receptor Modulator, LM11A-31, Improves Erectile Function in a Mouse Model of Cavernous Nerve Injury. J Sex Med 2021;18:17-28.

Silencing p75(NTR) prevents proNGF-induced endothelial cell death and development of acellular capillaries in rat retina

Accumulation of the nerve growth factor precursor (proNGF) and its receptor p75(NTR) have been associated with several neurodegenerative diseases in both brain and retina. However, whether proNGF contributes to microvascular degeneration remain unexplored. This study seeks to investigate the mechanism by which proNGF/p75(NTR) induce endothelial cell (EC) death and development of acellular capillaries, a surrogate marker of retinal ischemia. Stable overexpression of the cleavage-resistant proNGF and molecular silencing of p75(NTR) were utilized in human retinal EC and rat retinas in vivo. Stable overexpression of proNGF decreased NGF levels and induced retinal vascular cell death evident by 1.9-fold increase in acellular capillaries and activation of JNK and cleaved-PARP that were mitigated by p75(NTR)shRNA. In vitro, overexpression of proNGF did not alter TNF-α level, reduced NGF, however induced EC apoptosis evident by activation of JNK and p38 MAPK, cleaved-PARP. Silencing p75(NTR) using siRNA restored expression of NGF and TrkA activation and prevented EC apoptosis. Treatment of EC with human-mutant proNGF induced apoptosis that coincided with marked protein interaction and nuclear translocation of p75(NTR) and the neurotrophin receptor interacting factor. These effects were abolished by a selective p75(NTR) antagonist. Therefore, targeting p75(NTR) represents a potential therapeutic strategy for diseases associated with aberrant expression of proNGF.

Signaling of the neurotrophin receptor p75 in relation to Alzheimer's disease

The cellular mechanism of neuronal apoptosis in Alzheimer's disease (AD) is poorly understood. Many hypotheses have been put fourth to explain the underlying reason for neuro-degeneration in AD. Here, it is demonstrated that all neurotrophins that activated p75, without co-activation of the relevant Trk co-receptor, mediated apoptosis in hippocampal neurons. Thus, proneurotrophins and amyloid beta peptides (Abeta) can induce p75-mediated apoptosis in hippocampal neurons since they do not bind or activate Trk receptors. Based on the combined effects of aging, proneurotrophins, neurotrophins, and Abeta, a novel model of pathogenesis in AD is proposed. This mini-review explores the ligand and cell type based signaling pathways of the neurotrophin receptor p75 relating to Alzheimer's disease.

Genetic control of programmed cell death during animal development

The elimination of unwanted cells by programmed cell death is a common feature of animal development. Genetic studies in the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the mouse have not only revealed the molecular machineries that cause the programmed demise of specific cells, but have also allowed us to get a glimpse of the types of pathways that regulate these machineries during development. Rather than serving as a broad overview of programmed cell death during development, this review focuses on recent advances in our understanding of the regulation of specific programmed cell death events during nematode, fly, and mouse development. Recent studies have revealed that many of the regulatory pathways involved play additional important roles in development, which confirms that the programmed cell death fate is an integral aspect of animal development.

Ligand-Dependent Cleavage of the P75 Neurotrophin Receptor Is Necessary for NRIF Nuclear Translocation and Apoptosis in Sympathetic Neurons

The p75 neurotrophin receptor regulates neuronal survival, promoting it in some contexts yet activating apoptosis in others. The mechanism by which the receptor elicits these differential effects is poorly understood. Here, we demonstrate that p75 is cleaved by gamma-secretase in sympathetic neurons, specifically in response to proapoptotic ligands. This cleavage resulted in ubiquitination and subsequent nuclear translocation of NRIF, a DNA binding protein essential for p75-mediated apoptosis. Inhibition of gamma-secretase or expression of a mutant p75 resistant to this protease prevented receptor proteolysis, blocked NRIF nuclear entry, and prevented apoptosis. In contrast, overexpression of the p75 ICD resulted in NRIF nuclear accumulation and apoptosis. The receptor proteolysis and NRIF nuclear localization were also observed in vivo during naturally occurring cell death in the superior cervical ganglia. These results indicate that p75-mediated apoptosis requires gamma-secretase dependent release of its ICD, which facilitates nuclear translocation of NRIF.

Role of brain-derived neurotrophic factor in eating disorders: recent findings and its pathophysiological implications

Eating disorders, which include anorexia nervosa (AN) and bulimia nervosa (BN), are disorders characterized by abnormal patterns of weight regulation and eating behaviors, and by disturbances in attitudes and perceptions toward weight and body shape. Brain-derived neurotrophic factor (BDNF) plays a critical role in regulating neural survival, development, function, and plasticity in the brain. Recent findings using heterozygous BDNF (+/-) knock-out (reduced BDNF levels) mice have provided evidence that BDNF plays a role in regulating eating behaviors. Recently, we found that serum levels of BDNF in patients with eating disorders are significantly decreased compared with normal controls. In addition, an association between the BDNF gene polymorphism and eating disorders has been demonstrated. We reviewed the role of BDNF in the pathophysiology of eating disorders and the BDNF gene as a susceptibility gene for eating disorders. Considering the low levels of BDNF in patients with eating disorders, using drugs that increase the BDNF levels and/or BDNF gene therapy are possible novel therapeutic approaches. Providing confirmation that the BDNF gene is the true susceptibility gene for eating disorders could lead to rapid therapeutic progress in treating these disorders. In addition, a more complete understanding of the signal transduction pathway via the p75 neurotrophin receptor (p75NTR) and TrkB receptors would provide new perspectives for treating eating disorders.