Achille Gravanis

Context: Nerve growth factor (NGF) affects the development and survival of sympathetic neurons. NGF is also found in non-neural cell lineages that are implicated in immune-endocrine interactions associated with metabolic diseases. Although NGF is expressed in white adipose tissue (WAT), little is known about the regulation of its expression and role in adipocytes. Objective: To determine whether NGF and its receptors are expressed in human adipocytes and demonstrate their role in adipocyte metabolic and inflammatory phenotypes. Methods: The expression of NGF and its receptors, tropomyosin-related kinase A (TrkA) and pan-neurotrophin receptor (p75NTR), and their effects on metabolic and inflammatory responses were examined in freshly isolated adipocytes from human abdominal WAT and mouse 3T3L1 cells. Results: TrkA and p75NTR were expressed in both human and mouse adipocytes and pre-adipocytes. NGF was secreted by human white adipocytes and their exogenous exposure to NGF increased mitochondrial mass and activity, peroxisome proliferator-activated receptor gamma, CCAAT/enhancer binding protein alpha, and adiponectin levels. Additionally, NGF increased lipolysis in human WAT explants and suppressed lipids accumulation, lipoprotein lipase, and pro-inflammatory mediators interleukin (IL)-6 and IL-8 in human white adipocytes. The pro-inflammatory factor lipopolysaccharide downregulated the levels of NGF receptors in human white adipocytes. NGF also affected mitochondrial activity in both human and mouse pre-adipocytes and TrkA appeared to mediate, at least partially, the effects of NGF on adipocytes. Conclusion: Our data suggest that NGF is produced locally within the adipose tissue where it upregulates mitochondrial function while it suppresses the pro-inflammatory phenotype of human and mouse adipocytes.

Emerging neurotrophin treatments for optic nerve injury (ONI) aim to prevent the loss of retinal ganglion cells (RGCs) and enhance axonal regeneration. Microneurotrophins (MNTs), small‐molecule mimetics of neurotrophins, have shown neuroprotective effects in various animal models of neurodegeneration, yet MNT effects on ONI remain unknown. Here, we study the effects of BNN27, a MNT that mimics NGF, in a mouse model of optic nerve crush (ONC) and compare the targeted administration via biomaterial grafts placed around the ONC lesion against standard eye drop delivery. Compared to eye drop delivery, targeted biomaterial‐based BNN27 delivery resulted in more consistent and efficient RGC neuroprotection and reduced microglia‐mediated inflammation in the ONC lesion. Our findings demonstrate that targeted delivery of MNTs can alleviate key consequences of ONI and, therefore, be an essential part of effective combinatorial ONI treatments.

During tissue injury or infection, leukocytes are activated to produce proinflammatory mediators, which trigger the immune system to produce anti-inflammatory and analgesic molecules. Our previous studies provide evidence that synthetic microneurotrophins, like BNN27, exert significant analgesic and anti-inflammatory effects during Complete Freund’s Adjuvant (CFA)-induced inflammation and pain. Thus, the aim of the present study was to examine if the effect of BNN27 on inflammatory pain is mediated at least in part by activation of T-lymphocytes. For this purpose, six hours following the injection of CFA, spleens were harvested in PBS and lymphocytes were collected and placed in medium containing concanavalin-A and IL-2 to prompt T-lymphocyte proliferation and differentiation. Cells were then treated with BNN27 at different concentrations and the media and cells were collected for ELISA and PCR assays. The proliferation rate of T-cells was also examined using the MTT assay. Our results showed that BNN27 significantly increased the proliferation of T-lymphocytes. In addition, BNN27 significantly decreased IL-6 and TNF-α protein levels, while it increased the mRNA expression of μ-opioid receptor and opioid peptides PENK and POMC at different time points. Our data demonstrate considerable anti-inflammatory and analgesic effects of BNN27, making it a promising molecule for inflammation and pain management.

During tissue injury or infection, leukocytes are activated to produce proinflammatory mediators, which trigger the immune system to produce anti-inflammatory and analgesic molecules. Our previous studies provide evidence that synthetic microneurotrophins, like BNN27, exert significant analgesic and anti-inflammatory effects during Complete Freund’s Adjuvant (CFA)-induced inflammation and pain. Thus, the aim of the present study was to examine if the effect of BNN27 on inflammatory pain is mediated at least in part by activation of T-lymphocytes. For this purpose, six hr following the injection of CFA, spleens were harvested in PBS, lymphocytes were collected and placed in medium containing concanavalin-A and IL-2 to prompt T-lymphocyte proliferation and differentiation. Cells were then treated with BNN27 at different concentrations and the media and cells were collected for ELISA and PCR assays. The proliferation rate of T-cells was also examined using the MTT assay. Our results showed that BNN27 significantly increased the proliferation of T-lymphocytes. In addition, BNN27 significantly decreased IL-6 and TNF-α protein levels, while it increased the mRNA expression of μ-opioid receptor and opioid peptides PENK and POMC at different time points. Our data demonstrate considerable anti-inflammatory and analgesic effects of BNN27, making it a promising molecule for inflammation and pain management.

One common event that is the most detrimental in neurodegenerative disorders, even though they have a complex pathogenesis, is the increased rate of neuronal death. Endogenous neurotrophins consist of the major neuroprotective factors, while brain-derived neurotrophic factor (BDNF) and its high-affinity tyrosine kinase receptor TrkB are described in a number of studies for their important neuronal effects. Normal function of this receptor is crucial for neuronal survival, differentiation, and synaptic function. However, studies have shown that besides direct activation, the TrkB receptor can be transactivated via GPCRs. It has been proven that activation of the 5-HT₄ receptor and transactivation of the TrkB receptor have a positive influence on neuronal differentiation (total dendritic length, number of primary dendrites, and branching index). Because of that and based on the main structural characteristics of LM22A-4, a known activator of the TrkB receptor, and RS67333, a partial 5-HT₄ receptor agonist, we have designed and synthesized a small data set of novel compounds with potential dual activities in order to not only prevent neuronal death, but also to induce neuronal differentiation in neurodegenerative disorders.

Recent findings highlight myelin breakdown as a decisive early event in Alzheimer's Disease (AD) acting as aggravating factor of its progression. However, it is still unclear whether myelin loss is attributed to increased oligodendrocyte vulnerability, reduced repairing capacity or toxic stimuli. In the present study, we sought to clarify the starting point of myelin disruption accompanied with Oligodendrocyte Progenitor Cell (OPC) elimination in the brain of the 5xFAD mouse model of AD at 6 months of age in Dentate Gyrus of the hippocampus in relation to neurotrophin system. Prominent inflammation presence was detected since the age of 6 months playing a key role in myelin disturbance and AD progression. Expression analysis of neurotrophin receptors in OPCs was performed to identify new targets that could increase myelination in health and disease. OPCs in both control and 5xFAD mice express TrkB, TrkC and p75 receptors but not TrkA. Brain‐derived neurotrophic factor (BDNF) that binds to TrkB receptor is well‐known about its pro‐myelination effect, promoting oligodendrocytes proliferation and differentiation, so we focused our investigation on its effects in OPCs under neurodegenerative conditions. Our in vitro results showed that BDNF rescues OPCs from death and promotes their proliferation and differentiation in presence of the toxic Amyloid‐β 1‐42. Collectively, our results indicate that BDNF possess an additional neuroprotective role through its actions on oligodendrocytic component and its use could be proposed as a drug‐based myelin‐enhancing strategy, complementary to amyloid and tau centered therapies in AD.

Neurodegenerative diseases are incurable and debilitating conditions, characterized by progressive loss and degeneration of vulnerable neuronal populations. Currently, there are no effective therapies available for the treatment of most neurodegenerative disorders. A panel of extracts exhibiting interesting chemical profiles among a high number of bacterial strains isolated from East Mediterranean marine sediments and macroorganisms were evaluated for their activity on TrkB-expressing cells. Among them, the actinobacterial strain Streptomyces sp. BI0788, exhibiting neuroprotective activity in vitro, was selected and cultivated in large-scale. The chemical analysis of its organic extract resulted in the isolation of four new butanolides (1, 4–6), along with two previously reported butanolides (2 and 3) and eight previously reported butenolides (7–14). Compounds 2–4 and 7–14 were evaluated for their neuroprotective effects on TrkB-expressing NIH-3T3 cells. Among them, metabolites 3, 4, 7, 10, 11, 13 and 14 exhibited significant protective activity on the aforementioned cells through the activation of TrkB, the high-affinity receptor for the Brain-Derived Neurotrophic Factor (BDNF), which is well known to play a crucial role in neuronal cell survival and maintenance.

Neuronal cell fate is predominantly controlled based on the effects of growth factors, such as neurotrophins, and the activation of a variety of signaling pathways acting through neurotrophin receptors, namely Trk and p75 (p75NTR). Despite their beneficial effects on brain function, their therapeutic use is compromised due to their polypeptidic nature and blood–brain-barrier impermeability. To overcome these limitations, our previous studies have proven that DHEA-derived synthetic analogs can act like neurotrophins, as they lack endocrine side effects. The present study focuses on the biological characterization of a newly synthesized analog, ENT-A044, and its role in inducing cell-specific functions of p75NTR. We show that ENT-A044 can induce cell death and phosphorylation of JNK protein by activating p75NTR. Additionally, ENT-A044 can induce the phosphorylation of TrkB receptor, indicating that our molecule can activate both neurotrophin receptors, enabling the protection of neuronal populations that express both receptors. Furthermore, the present study demonstrates, for the first time, the expression of p75NTR in human-induced Pluripotent Stem Cells-derived Neural Progenitor Cells (hiPSC-derived NPCs) and receptor-dependent cell death induced via ENT-A044 treatment. In conclusion, ENT-A044 is proposed as a lead molecule for the development of novel pharmacological agents, providing new therapeutic approaches and research tools, by controlling p75NTR actions.

Neuronal cell fate is predominantly controlled by the effects of growth factors, such as neurotrophins, and the activation of a variety of signaling pathways acting through neurotrophin receptors, namely Trk and p75 (p75NTR). Despite their beneficial effects on brain function, their therapeutic use is compromised, due to their polypeptidic nature and blood–brain-barrier impermeability. To overcome these limitations, our previous studies have proven that DHEA-derived synthetic analogs can act like neurotrophins, lacking endocrine side effects. The present study focuses on the biological characterization of a newly synthesized analog, ENT-A044, and its role on inducing cell specific functions of p75NTR. We show that ENT-A044 can induce cell death and phosphorylation of JNK protein by activating p75NTR. Additionally, ENT-A044 can induce the phosphorylation of TrkB receptor, indicating that our molecule can activate both neurotrophin receptors, leading towards the protection of neuronal populations that express both receptors. Furthermore, the present study demonstrates for the first time the expression of p75NTR in human induced Pluripotent Stem Cells - derived Neural Progenitor Cells (hiPSCs - derived NPCs) and receptor-dependent cell death induced by ENT-A044 treatment. In conclusion, ENT-A044 could be proven a lead molecule for the development of novel pharmacological agents, aiming on new therapeutic approaches and research tools, by controlling p75NTR actions.