Potential role of hippocampal neurogenesis in spinal cord injury induced post-trauma depression

It has been reported both in clinic and rodent models that beyond spinal cord injury directly induced symptoms, such as paralysis, neuropathic pain, bladder/bowel dysfunction, and loss of sexual function, there are a variety of secondary complications, including memory loss, cognitive decline, depression, and Alzheimer's disease. The largescale longitudinal population-based studies indicate that post-trauma depression is highly prevalent in spinal cord injury patients. Yet, few basic studies have been conducted to address the potential molecular mechanisms. One of possible factors underlying the depression is the reduction of adult hippocampal neurogenesis which may come from less physical activity, social isolation, chronic pain, and elevated neuroinflammation after spinal cord injury. However, there is no clear consensus yet. In this review, we will first summarize the alteration of hippocampal neurogenesis post-spinal cord injury. Then, we will discuss possible mechanisms underlie this important spinal cord injury consequence. Finally, we will outline the potential therapeutic options aimed at enhancing hippocampal neurogenesis to ameliorate depression.

Regulator of G protein signaling 6 mediates exercise-induced recovery of hippocampal neurogenesis,learning,and memory in a mouse model of Alzheimer’s disease

Hippocampal neuronal loss causes cognitive dysfunction in Alzheimer’s disease.Adult hippocampal neurogenesis is reduced in patients with Alzheimer’s disease.Exercise stimulates adult hippocampal neurogenesis in rodents and improves memory and slows cognitive decline in patients with Alzheimer’s disease.However,the molecular pathways for exercise-induced adult hippocampal neurogenesis and improved cognition in Alzheimer’s disease are poorly understood.Recently,regulator of G protein signaling 6(RGS6)was identified as the mediator of voluntary running-induced adult hippocampal neurogenesis in mice.Here,we generated novel RGS6fl/fl;APP_(SWE) mice and used retroviral approaches to examine the impact of RGS6 deletion from dentate gyrus neuronal progenitor cells on voluntary running-induced adult hippocampal neurogenesis and cognition in an amyloid-based Alzheimer’s disease mouse model.We found that voluntary running in APP_(SWE) mice restored their hippocampal cognitive impairments to that of control mice.This cognitive rescue was abolished by RGS6 deletion in dentate gyrus neuronal progenitor cells,which also abolished running-mediated increases in adult hippocampal neurogenesis.Adult hippocampal neurogenesis was reduced in sedentary APP_(SWE) mice versus control mice,with basal adult hippocampal neurogenesis reduced by RGS6 deletion in dentate gyrus neural precursor cells.RGS6 was expressed in neurons within the dentate gyrus of patients with Alzheimer’s disease with significant loss of these RGS6-expressing neurons.Thus,RGS6 mediated voluntary running-induced rescue of impaired cognition and adult hippocampal neurogenesis in APP_(SWE) mice,identifying RGS6 in dentate gyrus neural precursor cells as a possible therapeutic target in Alzheimer’s disease.

Melatonin:a multitasking indoleamine to modulate hippocampal neurogenesis

Neurodegeneration affects a large number of cell types including neurons,astrocytes or oligodendrocytes,and neural stem cells.Neural stem cells can generate new neuronal populations through proliferation,migration,and differentiation.This neurogenic potential may be a relevant factor to fight neurodegeneration and aging.In the last years,we can find growing evidence suggesting that melatonin may be a potential modulator of adult hippocampal neurogenesis.The lack of therapeutic strategies targeting neurogenesis led researchers to explore new molecules.Numerous preclinical studies with melatonin observed how melatonin can modulate and enhance molecular and signaling pathways involved in neurogenesis.We made a special focus on the connection between these modulation mechanisms and their implication in neurodegeneration,to summarize the current knowledge and highlight the therapeutic potential of melatonin.

Exploration of the mechanism by which icariin modulates hippocampal neurogenesis in a rat model of depression

Icariin(ICA) has a significant capacity to protect against depression and hippocampal injury,but it cannot effectively cross the bloodbrain barrier and accumulate in the brain.Therefore,the mechanism by which ICA protects against hippocampal injury in depression remains unclear.In this study,we performed proteomics analysis of cerebrospinal fluid to investigate the mechanism by which ICA prevents dysfunctional hippocampal neurogenesis in depression.A rat model of depression was established through exposure to chronic unpredictable mild stress for 6 weeks,after which 120 mg/kg ICA was administered subcutaneously every day.The results showed that ICA alleviated depressive symptoms,learning and memory dysfunction,dysfunctional neurogenesis,and neuronal loss in the dentate gyrus of rats with depression.Neural stem cells from rat embryonic hippocampi were cultured in media containing 20% cerebrospinal fluid from each group of rats and then treated with 100 μM corticosterone.The addition of cerebrospinal fluid from rats treated with ICA largely prevented the corticosterone-mediated inhibition of neuronal proliferation and differentiation.Fifty-two differentially expressed proteins regulated by chronic unpredictable mild stress and ICA were identified through proteomics analysis of cerebrospinal fluid.These proteins were mainly involved in the ribosome,PI3 K-Akt signaling,and interleukin-17 signaling pathways.Parallel reaction monitoring mass spectrometry showed that Rps4 x,Rps12,Rps14,Rps19,Hsp90 b1,and Hsp90 aa1 were up-regulated by chronic unpredictable mild stress and down-regulated by ICA.In contrast,Htr A1 was down-regulated by chronic unpredictable mild stress and up-regulated by ICA.These findings suggest that ICA can prevent depression and dysfunctional hippocampal neurogenesis through regulating the expression of certain proteins found in the cerebrospinal fluid.The study was approved by the Experimental Animal Ethics Committee of Guangzhou University of Chinese Medicine of China in March 2017.

Impact of pediatric traumatic brain injury on hippocampal neurogenesis

Traumatic brain injury(TBI)is a major cause of mortality and morbidity in the pediatric population.With advances in medical care,the mortality rate of pediatric TBI has declined.However,more children and adolescents are living with TBI-related cognitive and emotional impairments,which negatively affects the quality of their life.Adult hippocampal neurogenesis plays an important role in cognition and mood regulation.Alterations in adult hippocampal neurogenesis are associated with a variety of neurological and neurodegenerative diseases,including TBI.Promoting endogenous hippocampal neurogenesis after TBI merits significant attention.However,TBI affects the function of neural stem/progenitor cells in the dentate gyrus of hippocampus,which results in aberrant migration and impaired dendrite development of adult-born neurons.Therefore,a better understanding of adult hippocampal neurogenesis after TBI can facilitate a more successful neuro-restoration of damage in immature brains.Secondary injuries,such as neuroinflammation and oxidative stress,exert a significant impact on hippocampal neurogenesis.Currently,a variety of therapeutic approaches have been proposed for ameliorating secondary TBI injuries.In this review,we discuss the uniqueness of pediatric TBI,adult hippocampal neurogenesis after pediatric TBI,and current efforts that promote neuroprotection to the developing brains,which can be leveraged to facilitate neuroregeneration.

Adult hippocampal neurogenesis and its impairment in Alzheimer's disease

Adult neurogenesis is the creation of new neurons which integrate into the existing neural circuit of the adult brain.Recent evidence suggests that adult hippocampal neurogenesis(AHN)persists throughout life in mammals,including humans.These newborn neurons have been implicated to have a crucial role in brain functions such as learning and memory.Importantly,studies have also found that hippocampal neurogenesis is impaired in neurodegenerative and neuropsychiatric diseases.Alzheimer’s disease(AD)is one of the most common forms of dementia affecting millions of people.Cognitive dysfunction is a common symptom of AD patients and progressive memory loss has been attributed to the degeneration of the hippocampus.Therefore,there has been growing interest in identifying how hippocampal neurogenesis is affected in AD.However,the link between cognitive decline and changes in hippocampal neurogenesis in AD is poorly understood.In this review,we summarized the recent literature on AHN and its impairments in AD.

A new age in understanding adult hippocampal neurogenesis in Alzheimer’s disease

Several lines of evidence have established that proliferation and differentiation of neural stem cells into neurons within the sub-granular zone of the dentate gyrus,a process named adult hippocampal neurogenesis,contribute to maintaining healthy cognitive functions throughout life.The rate of adult hippocampal neurogenesis decreases with aging and a premature impairment of adult hippocampal neurogenesis has been observed both in animal models of Alzheimer’s disease and human post-mortem tissues.The causal relationship between adult hippocampal neurogenesis and the development of Alzheimer’s disease pathology has,however,not been established.This is partly due to the limitation of recapitulating the development of Alzheimer’s disease pathology in rodent models and the lack of translatable biomarkers to identify tractable targets in humans.While it is tempting to postulate that adult hippocampal neurogenesis could be leveraged to improve cognitive deficits in Alzheimer’s disease,consensual results have yet to be reached to fully explore this hypothesis.In this review,we discuss how the recent progress in identifying molecular pathways in adult hippocampal neurogenesis provides a good framework to initiate strategies for drug-based intervention in neurodegenerative diseases,especially in Alzheimer’s disease.We outline how discrepancies in pre-clinical disease models and experimental methodology have resulted in contradictory findings and propose a shift towards using more translatable approaches to model neurogenesis in Alzheimer’s disease.In particular,we review how exploring novel experimental paradigms including the use of human induced pluripotent stem cells and more complex cell culture systems,as well as standardizing protocols used to investigate evidence of neurogenesis in human tissues,could deliver deeper mechanistic insights that would kick-start innovative drug discovery efforts to promote healthy aging and cellular rejuvenation.

Exercise and hippocampal neurogenesis: a dogma re-examined and lessons learned

Exercise is a potent force of nature with significant potential for extending longevity and boosting physical fitness. It is also be- ing increasingly used as a prophylactic and curative measure for various physical ailments, such as cardiovascular diseases and diabetes.

Active fraction combination from Liuwei Dihuang decoction improves adult hippocampal neurogenesis and neurogenic microenvironment in cranially irradiated mice

OBJECTIVE Cranial radiotherapy is clinically used in the treatment of brain tumors;however,the consequent cognitive and emotional dysfunctions seriously impair the life quality of patients.LW-AFC,an active fraction combination extracted from classical traditional Chinese medicine prescription Liuwei Dihuang decoction,can improve cognitive and emotional dysfunctions in many animal models;however,the protective effect of LW-AFC on cranial irradiation-induced cognitive and emotional dysfunctions has not been reported.Recent studies indicate that impairment of adult hippocampal neurogenesis(AHN)and alterations of the neurogenic microenvironment in the hippocampus constitute critical factors in cognitive and emotional dysfunctions following cranial irradiation.Here,our research further investigated the potential protective effects and mechanisms of LW-AFC on cranial irradiation-induced cognitive and emotional dysfunctions in mice.METHODS LW-AFC(1.6 g·kg^(-1))was intragastrically administered to mice for 14 d before cranial irradiation(7 Gyγ-ray).AHN was examined by quantifying the number of proliferative neural stem cells and immature neurons in the dorsal and ventral hippocampus.The contextual fear conditioning test,open field test,and tail suspension test were used to assess cognitive and emotional functions in mice.To detect the change of the neurogenic microenvironment,colorimetry and multiplex bead analysis were performed to measure the level of oxidative stress,neurotrophic and growth factors,and inflammation in the hippocampus.RESULTS LW-AFC exerted beneficial effects on the contextual fear memory,anxiety behavior,and depression behavior in irradiated mice.Moreover,LW-AFC increased the number of proliferative neural stem cells and immature neurons in the dorsal hippocampus,displaying a regional specificity of neurogenic response.For the neurogenic microenvironment,LW-AFC significantly increased the contents of superoxide dismutase,glutathione peroxidase,glutathione,and catalase and decreased the content of malondialdehyde in the hippocampus of irradiated mice,accompanied by the increase in brain-derived neurotrophic factor,insulin-like growth factor-1,and interleukin-4 content.Together,LW-AFC improved cognitive and emotional dysfunctions,promoted AHN preferentially in the dorsal hippocampus,and ameliorated disturbance in the neurogenic microenvironment in irradiated mice.CONCLUSION LW-AFC ameliorates cranial irradiation-induced cognitive and emotional dysfunctions,and the underlying mechanisms are mediated by promoting AHN in the dorsal hippocampus and improving the neurogenic microenvironment.LW-AFC might be a promising therapeutic agent to treat cognitive and emotional dysfunctions in patients receiving cranial radiotherapy.

Hippocampal PPARδ downregulation contri butes to depressive phenotype with decreased neurogenesis

Our previous study showed that up-regulating hippocampal peroxisome proliferator-activated receptorδ(PPARδ)displays an antidepressive effect and enhanc-es hippocampal neurogenesis in the context of chronic stress.Here,the changes in depressive behaviors and hippocampal neurogenesis were investigated after PPARδknockdown by microinfusion of the lentiviral vector,expressing short hairpin RNA(sh RNA)complementary to the coding exon of PPARδ,into the bilateral dentate gyri of the hippocampus or PPARδblockade by repeated systemic administration of PPARδantagonist,GSK0660(1 or 3mg·kg-1,ip,for 21 d).We found that hippocampal PPARδknockdown or blockade induced depressive-like behaviors and increased vulnerability to stress,which is involved in decreased hippocampal neurogenesis and neuronal differentiation.Down-regulating hippocampal PPARδalso induced significant decreases in phosphorylation c AMP response element-binding protein(CREB)and BDNF level in the hippocampus.The in vitro study that PPARδknockdown or blockade inhibited proliferation and differentiation of neural stem cells.Taken together,our results suggest that PPARδcould be a novel and promising target for developing new PPARδagonists for the treatment of depressive disorders.

β‑Hydroxybutyric acid improves cognitive function in a model of heat stress by promoting adult hippocampal neurogenesis

Heat stress has multiple potential effects on the brain,such as neuroinflammation,neurogenesis defects,and cog-nitive impairment.β-hydroxybutyric acid(BHBA)has been demonstrated to play neuroprotective roles in various models of neurological diseases.In the present study,we investigated the efficacy of BHBA in alleviating heat stress-induced impairments of adult hippocampal neurogenesis and cognitive function,as well as the underlying mecha-nisms.Mice were exposed to 43℃for 15 min for 14 days after administration with saline,BHBA,or minocycline.Here,we showed for the first time that BHBA normalized memory ability in the heat stress-treated mice and attenuated heat stress-impaired hippocampal neurogenesis.Consistently,BHBA noticeably improved the synaptic plasticity in the heat stress-treated hippocampal neurons by inhibiting the decrease of synapse-associated proteins and the density of dendritic spines.Moreover,BHBA inhibited the expression of cleaved caspase-3 by suppressing endoplasmic reticu-lum(ER)stress,and increased the expression of brain-derived neurotrophic factor(BDNF)in the heat stress-treated hippocampus by activating the protein kinase B(Akt)/cAMP response element binding protein(CREB)and methyl-CpG binding protein 2(MeCP2)pathways.These findings indicate that BHBA is a potential agent for improving cogni-tive functions in heat stress-treated mice.The action may be mediated by ER stress,and Akt-CREB-BDNF and MeCP2 pathways to improve adult hippocampal neurogenesis and synaptic plasticity.

Efficacy of exercise rehabilitation for managing patients with Alzheimer's disease

Alzheimer's disease(AD) is a progressive and degenerative neurological disease characterized by the deterioration of cognitive functions. While a definitive cure and optimal medication to impede disease progression are currently unavailable, a plethora of studies have highlighted the potential advantages of exercise rehabilitation for managing this condition. Those studies show that exercise rehabilitation can enhance cognitive function and improve the quality of life for individuals affected by AD. Therefore, exercise rehabilitation has been regarded as one of the most important strategies for managing patients with AD. Herein, we provide a comprehensive analysis of the currently available findings on exercise rehabilitation in patients with AD, with a focus on the exercise types which have shown efficacy when implemented alone or combined with other treatment methods, as well as the potential mechanisms underlying these positive effects. Specifically, we explain how exercise may improve the brain microenvironment and neuronal plasticity. In conclusion, exercise is a cost-effective intervention to enhance cognitive performance and improve quality of life in patients with mild to moderate cognitive dysfunction. Therefore, it can potentially become both a physical activity and a tailored intervention. This review may aid the development of more effective and individualized treatment strategies to address the challenges imposed by this debilitating disease, especially in low-and middle-income countries.

Adult neural stem cells and schizophrenia

Schizophrenia(SCZ)is a devastating and complicated mental disorder accompanied by variable positive and negative symptoms and cognitive deficits.Although many genetic risk factors have been identified,SCZ is also considered as a neurodevelopmental disorder.Elucidation of the pathogenesis and the development of treatment is challenging because complex interactions occur between these genetic risk factors and environment in essential neurodevelopmental processes.Adult neural stem cells share a lot of similarities with embryonic neural stem cells and provide a promising model for studying neuronal development in adulthood.These adult neural stem cells also play an important role in cognitive functions including temporal and spatial memory encoding and context discrimination,which have been shown to be closely linked with many psychiatric disorders,such as SCZ.Here in this review,we focus on the SCZ risk genes and the key components in related signaling pathways in adult hippocampal neural stem cells and summarize their roles in adult neurogenesis and animal behaviors.We hope that this would be helpful for the understanding of the contribution of dysregulated adult neural stem cells in the pathogenesis of SCZ and for the identification of potential therapeutic targets,which could facilitate the development of novel medication and treatment.