Regeneration of neuromuscular synapses after acute and chronic denervation by inhibiting the gerozyme 15-prostaglandin dehydrogenase

Inhibiting 15-PGDH blocks blood-brain barrier deterioration and protects mice from Alzheimer's disease and traumatic brain injury

Alzheimer's disease (AD) and traumatic brain injury (TBI) are currently untreatable neurodegenerative disorders afflicting millions of people worldwide. These conditions are pathologically related, and TBI is one of the greatest risk factors for AD. Although blood-brain barrier (BBB) disruption drives progression of both AD and TBI, strategies to preserve BBB integrity have been hindered by lack of actionable targets. Here, we identify 15-hydroxyprostaglandin dehydrogenase (15-PGDH), an enzyme that catabolizes eicosanoids and other anti-inflammatory mediators, as a therapeutic candidate that protects the BBB. We demonstrate that 15-PGDH is enriched in BBB-associated myeloid cells and becomes markedly elevated in human and mouse models of AD and TBI, as well as aging, another major risk factor for AD. Pathological increase in 15-PGDH correlates with pronounced oxidative stress, neuroinflammation, and neurodegeneration, alongside profound BBB structural degeneration characterized by astrocytic endfeet swelling and functional impairment. Pharmacologic inhibition or genetic reduction of 15-PGDH in AD and TBI models strikingly mitigates oxidative damage, suppresses neuroinflammation, and restores BBB integrity. Most notably, inhibiting 15-PGDH not only halts neurodegeneration but also preserves cognitive function at levels indistinguishable from healthy controls. Remarkably, these neuroprotective effects in AD are achieved without affecting amyloid pathology, underscoring a noncanonical mechanism for treating AD. In a murine microglia cell line exposed to amyloid beta oligomer, major protection was demonstrated by multiple anti-inflammatory substrates that 15-PGDH degrades. Thus, our findings position 15-PGDH inhibition as a broad-spectrum strategy to protect the BBB and thereby preserve brain health and cognition in AD and TBI.

Age-related impairment of intestinal inflammation resolution through an eicosanoid-immune-microbiota axis

Aging manifests a decline of immune function, induces microbiome dysbiosis, drives organ inflammation, and impedes the resolution of inflammation. However, the mechanisms underlying age-related intestinal inflammation remain poorly described. Here, we find that the resolution of T cell-initiated intestinal inflammation is impaired with aging. This impairment is mediated by disrupting the immune-microbiota interplay, controlled by intestinal eicosanoid metabolism. Pharmacologically inhibiting eicosanoid biosynthesis, blocking the prostaglandin E receptor subtype 4 (EP4), or genetically ablating EP4 diminishes age-related impairment of intestinal inflammation resolution. Mechanistically, mononuclear phagocyte-intrinsic eicosanoid-EP4 signaling impedes the resolution of intestinal inflammation through fostering gut microbial dysbiosis and, more importantly, interrupting segmented filamentous bacterial adhesion to the intestinal epithelium. Colonization with EP4-ablated mouse microbiota or segmented filamentous bacteria improves the resolution of intestinal inflammation. These findings reveal that eicosanoid-dependent immune-microbiota interactions impair inflammation resolution in the aged intestine, highlighting potential intervention strategies for improving age-related gut health.

Black phosphorus nanosheets fortified with catalase to enhance Schwann cell responses for neural repair

Peripheral nerve injuries (PNI) present a significant clinical challenge due to the complex cellular and molecular activities that hinder functional recovery. Schwann cells (SCs), the principal glial cells in the peripheral nervous system, play a vital role in neural repair by transitioning into a repairing phenotype capable of supporting axonal regrowth. However, these regenerative properties fade over time, leading to poor clinical outcomes. To address this issue, we engineered a black phosphorus nanosheet (BPNS) functionalized with catalase (BPNS@CAT) to modulate SC activity and enhance nerve regeneration. In vitro experiments demonstrated that BPNS@CAT reduced ROS levels, regulated the angiogenic and immunomodulatory functions of SCs. Mechanistically, we identified that BPNS@CAT activated the JAK/STAT pathway, which is crucial for SC-mediated repair processes. To validate its therapeutic potential, a BPNS@CAT-GelMA/PCL hydrogel scaffold was fabricated and applied in a rat sciatic nerve-crush model. The scaffold enhanced axonal regeneration, restored nerve function, and improved sensory, motor, and emotional behaviors. Our study broadens the range of BPNS applications in SC-based nerve repair and pave the way for future applications of BPNS in translational medicine.

Rescue of non-healing, degenerative salivary glands by cholinergic-calcium signaling

Chronic degenerative wounds are often deemed irreparable, directing research efforts to focus predominantly on acute tissue injury regeneration while leaving endogenous repair mechanisms for chronically damaged tissues largely unexplored. In this study, we demonstrate that non-healing, severely degenerated salivary gland tissues can be fundamentally restored through first-line treatment with muscarinic agonists. This approach rescues tissue structure and function, returning it to a homeostatic-like state, and reactivates endogenous regeneration processes to drive new cell expansion that persists for months post-treatment. Furthermore, neuromimetic activation profoundly depletes radiation-induced DNA damage and re-establishes the nerve-acinar relationship, ultimately restoring the tissues physiological capacity to maintain homeostasis, even in the absence of treatment. We show that full recovery of organ function, comparable to uninjured controls, is primarily mediated by the re-differentiation of aberrantly de-differentiated epithelial acinar cells and the restoration of mitochondrial function via a muscarinic-calcium signaling pathway. These findings challenge the prevailing notion that chronic organ degeneration is irreversible and propose a readily testable therapeutic strategy for epithelial restoration with potential applications across a spectrum of chronic injuries.

Succinate Regulates Exercise-Induced Muscle Remodelling by Boosting Satellite Cell Differentiation Through Succinate Receptor 1

BACKGROUND

Skeletal muscle remodelling can cause clinically important changes in muscle phenotypes. Satellite cells (SCs) myogenic potential underlies the maintenance of muscle plasticity. Accumulating evidence shows the importance of succinate in muscle metabolism and function. However, whether succinate can affect SC function and subsequently coordinate muscle remodelling to exercise remains unexplored.

METHODS

A mouse model of high-intensity interval training (HIIT) was used to investigate the effects of succinate on muscle remodelling and SC function by exercise capacity test and biochemical methods. Mice with succinate receptor 1 (SUCNR1)-specific knockout in SCs were generated as an in vivo model to explore the underlying mechanisms. RNA sequencing of isolated SCs was performed to identify molecular changes responding to succinate-SUCNR1 signalling. The effects of identified key molecules on the myogenic capacity of SCs were investigated using gain- and loss-of-function assays in vitro. To support the translational application, the clinical efficacy of succinate was explored in muscle-wasting mice.

RESULTS

After 21 days of HIIT, mice supplemented with 1.5% succinate exhibited striking gains in grip strength (+0.38 ± 0.04 vs. 0.26 ± 0.03 N, p < 0.001) and endurance (+276.70 ± 55.80 vs. 201.70 ± 45.31 s, p < 0.05), accompanied by enhanced muscle hypertrophy and neuromuscular junction regeneration (p < 0.001). The myogenic capacity of SCs was significantly increased in gastrocnemius muscle of mice supplemented with 1% and 1.5% succinate (+16.48% vs. control, p = 0.008; +47.25% vs. control, p < 0.001, respectively). SUCNR1-specific deletion in SCs abolished the modulatory influence of succinate on muscle adaptation in response to exercise, revealing that SCs respond to succinate-SUCNR1 signalling, thereby facilitating muscle remodelling. SUCNR1 signalling markedly upregulated genes associated with stem cell differentiation and phosphorylation pathways within SCs, of which p38α mitogen-activated protein kinase (MAPK; fold change = 6.7, p < 0.001) and protein kinase C eta (PKCη; fold change = 12.5, p < 0.001) expressions were the most enriched, respectively. Mechanistically, succinate enhanced the myogenic capacity of isolated SCs by activating the SUCNR1-PKCη-p38α MAPK pathway. Finally, succinate promoted SC differentiation (1.5-fold, p < 0.001), ameliorating dexamethasone-induced muscle atrophy in mice (p < 0.001).

CONCLUSIONS

Our findings reveal a novel function of succinate in enhancing SC myogenic capacity via SUCNR1, leading to enhanced muscle adaptation in response to exercise. These findings provide new insights for developing pharmacological strategies to overcome muscle atrophy-related diseases.

Excessive alcohol intake produces persistent mechanical allodynia and dysregulates the endocannabinoid system in the lumbar dorsal root ganglia of genetically-selected Marchigian Sardinian alcohol-preferring rats

Epidemiological data indicate a strong association between alcohol use disorder (AUD) and neuropathic pain. Genetically-selected Marchigian Sardinian alcohol-preferring (msP) rats exhibit a high preference for alcohol compared with their background strain (Wistar rats), but their sensitivity to mechanical allodynia after chronic alcohol exposure is unknown. The present study compared the development of mechanical allodynia between "low, non-pathological drinker" Wistar rats and "high drinker" msP rats using the two-bottle choice (2BC) free-access procedure. Several studies reported the involvement of endocannabinoids (eCBs) in modulating mechanical allodynia, but there are no data on their role in alcohol-related allodynia. Thus, the present study assessed eCBs and their related lipid species in lumbar dorsal root ganglia (DRG) and correlated them with mechanical allodynia in our model. We found that male and female msP rats developed persistent mechanical allodynia during protracted abstinence from alcohol, presenting no sign of recovery, as opposed to Wistar rats. This effect directly correlated with their total alcohol intake. Notably, we found a correlation between lower lumbar DRG 2-arachidonoylglycerol (2-AG) levels and the development of higher mechanical allodynia during abstinence in msP rats of both sexes but not in Wistar rats. Moreover, alcohol-exposed and abstinent msP and Wistar females but not males exhibited significant alterations of thromboxane B2 and prostaglandin E2/prostaglandin D2 compared with naive rats. These findings demonstrate that DRG 2-AG metabolism is altered in msP rats during prolonged abstinence and represents a potentially interesting pharmacological target for the treatment of mechanical allodynia during alcohol abstinence.

Muscle-resident mesenchymal progenitors sense and repair peripheral nerve injury via the GDNF-BDNF axis

Fibro-adipogenic progenitors (FAPs) are muscle-resident mesenchymal progenitors that can contribute to muscle tissue homeostasis and regeneration, as well as postnatal maturation and lifelong maintenance of the neuromuscular system. Recently, traumatic injury to the peripheral nerve was shown to activate FAPs, suggesting that FAPs can respond to nerve injury. However, questions of how FAPs can sense the anatomically distant peripheral nerve injury and whether FAPs can directly contribute to nerve regeneration remained unanswered. Here, utilizing single-cell transcriptomics and mouse models, we discovered that a subset of FAPs expressing GDNF receptors Ret and Gfra1 can respond to peripheral nerve injury by sensing GDNF secreted by Schwann cells. Upon GDNF sensing, this subset becomes activated and expresses Bdnf. FAP-specific inactivation of Bdnf (Prrx1Cre; Bdnffl/fl) resulted in delayed nerve regeneration owing to defective remyelination, indicating that GDNF-sensing FAPs play an important role in the remyelination process during peripheral nerve regeneration. In aged mice, significantly reduced Bdnf expression in FAPs was observed upon nerve injury, suggesting the clinical relevance of FAP-derived BDNF in the age-related delays in nerve regeneration. Collectively, our study revealed the previously unidentified role of FAPs in peripheral nerve regeneration, and the molecular mechanism behind FAPs' response to peripheral nerve injury.

A molecular pathway for cancer cachexia-induced muscle atrophy revealed at single-nucleus resolution

Cancer cachexia is a prevalent and often fatal wasting condition that cannot be fully reversed with nutritional interventions. Muscle atrophy is a central component of the syndrome, but the mechanisms whereby cancer leads to skeletal muscle atrophy are not well understood. We performed single-nucleus multi-omics on skeletal muscles from a mouse model of cancer cachexia and profiled the molecular changes in cachexic muscle. Our results revealed the activation of a denervation-dependent gene program that upregulates the transcription factor myogenin. Further studies showed that a myogenin-myostatin pathway promotes muscle atrophy in response to cancer cachexia. Short hairpin RNA inhibition of myogenin or inhibition of myostatin through overexpression of its endogenous inhibitor follistatin prevented cancer cachexia-induced muscle atrophy in mice. Our findings uncover a molecular basis of muscle atrophy associated with cancer cachexia and highlight potential therapeutic targets for this disorder.

Schwann cell-secreted PGE2 promotes sensory neuron excitability during development

Electrical excitability-the ability to fire and propagate action potentials-is a signature feature of neurons. How neurons become excitable during development and whether excitability is an intrinsic property of neurons remain unclear. Here, we demonstrate that Schwann cells, the most abundant glia in the peripheral nervous system, promote somatosensory neuron excitability during development. We find that Schwann cells secrete prostaglandin E2, which is necessary and sufficient to induce developing somatosensory neurons to express normal levels of genes required for neuronal function, including voltage-gated sodium channels, and to fire action potential trains. Inactivating this signaling pathway in Schwann cells impairs somatosensory neuron maturation, causing multimodal sensory defects that persist into adulthood. Collectively, our studies uncover a neurodevelopmental role for prostaglandin E2 distinct from its established role in inflammation, revealing a cell non-autonomous mechanism by which glia regulate neuronal excitability to enable the development of normal sensory functions.

Eicosanoid signaling in neuroinflammation associated with Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative condition affecting a substantial portion of the global population. It is marked by a complex interplay of factors, including the accumulation of amyloid plaques and tau tangles within the brain, leading to neuroinflammation and neuronal damage. Recent studies have underscored the role of free lipids and their derivatives in the initiation and progression of AD. Eicosanoids, metabolites of polyunsaturated fatty acids like arachidonic acid (AA), emerge as key players in this scenario. Remarkably, eicosanoids can either promote or inhibit the development of AD, and this multifaceted role is determined by how eicosanoid signaling influences the immune responses within the brain. However, the precise molecular mechanisms dictating the dual role of eicosanoids in AD remain elusive. In this comprehensive review, we explore the intricate involvement of eicosanoids in neuronal function and dysfunction. Furthermore, we assess the therapeutic potential of targeting eicosanoid signaling pathways as a viable strategy for mitigating or halting the progression of AD.

Denervation alters the secretome of myofibers and thereby affects muscle stem cell lineage progression and functionality

Skeletal muscle function crucially depends on innervation while repair of skeletal muscle relies on resident muscle stem cells (MuSCs). However, it is poorly understood how innervation affects MuSC properties and thereby regeneration of skeletal muscle. Here, we report that loss of innervation causes precocious activation of MuSCs concomitant with the expression of markers of myogenic differentiation. This aberrant activation of MuSCs after loss of innervation is accompanied by profound alterations on the mRNA and protein level. Combination of muscle injury with loss of innervation results in impaired regeneration of skeletal muscle including shifts in myogenic populations concomitant with delayed maturation of regenerating myofibers. We further demonstrate that loss of innervation leads to alterations in myofibers and their secretome, which then affect MuSC behavior. In particular, we identify an increased secretion of Osteopontin and transforming growth factor beta 1 (Tgfb1) by myofibers isolated from mice which had undergone sciatic nerve transection. The altered secretome results in the upregulation of early activating transcription factors, such as Junb, and their target genes in MuSCs. However, the combination of different secreted factors from myofibers after loss of innervation is required to cause the alterations observed in MuSCs after loss of innervation. These data demonstrate that loss of innervation first affects myofibers causing alterations in their secretome which then affect MuSCs underscoring the importance of proper innervation for MuSC functionality and regeneration of skeletal muscle.

Agonists of melatonin receptors strongly promote the functional recovery from the neuroparalysis induced by neurotoxic snakes

Snake envenoming is a major, but neglected, tropical disease. Among venomous snakes, those inducing neurotoxicity such as kraits (Bungarus genus) cause a potentially lethal peripheral neuroparalysis with respiratory deficit in a large number of people each year. In order to prevent the development of a deadly respiratory paralysis, hospitalization with pulmonary ventilation and use of antivenoms are the primary therapies currently employed. However, hospitals are frequently out of reach for envenomated patients and there is a general consensus that additional, non-expensive treatments, deliverable even long after the snake bite, are needed. Traumatic or toxic degenerations of peripheral motor neurons cause a neuroparalysis that activates a pro-regenerative intercellular signaling program taking place at the neuromuscular junction (NMJ). We recently reported that the intercellular signaling axis melatonin-melatonin receptor 1 (MT1) plays a major role in the recovery of function of the NMJs after degeneration of motor axon terminals caused by massive Ca2+ influx. Here we show that the small chemical MT1 agonists: Ramelteon and Agomelatine, already licensed for the treatment of insomnia and depression, respectively, are strong promoters of the neuroregeneration after paralysis induced by krait venoms in mice, which is also Ca2+ mediated. The venom from a Bungarus species representative of the large class of neurotoxic snakes (including taipans, coral snakes, some Alpine vipers in addition to other kraits) was chosen. The functional recovery of the NMJ was demonstrated using electrophysiological, imaging and lung ventilation detection methods. According to the present results, we propose that Ramelteon and Agomelatine should be tested in human patients bitten by neurotoxic snakes acting presynaptically to promote their recovery of health. Noticeably, these drugs are commercially available, safe, non-expensive, have a long bench life and can be administered long after a snakebite even in places far away from health facilities.