Mice lacking nerve growth factor display perinatal loss of sensory and sympathetic neurons yet develop basal forebrain cholinergic neurons

Nerve growth factor metabolic dysfunction in Alzheimer's disease and Down syndrome

Alzheimer's disease (AD) is a devastating neurodegenerative condition and the most common type of amnestic dementia in the elderly. Individuals with Down syndrome (DS) are at increased risk of developing AD in adulthood as a result of chromosome 21 trisomy and triplication of the amyloid precursor protein (APP) gene. In both conditions, the central nervous system (CNS) basal forebrain cholinergic system progressively degenerates, and such changes contribute to the manifestation of cognitive decline and dementia. Given the strong dependency of these neurons on nerve growth factor (NGF), it was hypothesized that their atrophy was caused by NGF deficits. However, in AD, the synthesis of NGF is not affected at the transcript level and there is a marked increase in its precursor, proNGF. This apparent paradox remained elusive for many years. In this review, we discuss the recent evidence supporting a CNS deficit in the extracellular metabolism of NGF, both in AD and in DS brains. We describe the nature of this trophic disconnection and its implication for the atrophy of basal forebrain cholinergic neurons. We further discuss the potential of NGF pathway markers as diagnostic indicators of a CNS trophic disconnection.

TNF-α/TNFR1 signaling is required for the development and function of primary nociceptors

Primary nociceptors relay painful touch information from the periphery to the spinal cord. Although it is established that signals generated by receptor tyrosine kinases TrkA and Ret coordinate the development of distinct nociceptive circuits, mechanisms modulating TrkA or Ret pathways in developing nociceptors are unknown. We have identified tumor necrosis factor (TNF) receptor 1 (TNFR1) as a critical modifier of TrkA and Ret signaling in peptidergic and nonpeptidergic nociceptors. Specifically, TrkA+ peptidergic nociceptors require TNF-α-TNFR1 forward signaling to suppress nerve growth factor (NGF)-mediated neurite growth, survival, excitability, and differentiation. Conversely, TNFR1-TNF-α reverse signaling augments the neurite growth and excitability of Ret+ nonpeptidergic nociceptors. The developmental and functional nociceptive defects associated with loss of TNFR1 signaling manifest behaviorally as lower pain thresholds caused by increased sensitivity to NGF. Thus, TNFR1 exerts a dual role in nociceptor information processing by suppressing TrkA and enhancing Ret signaling in peptidergic and nonpeptidergic nociceptors, respectively.

Netrin-1 controls sympathetic arterial innervation

Autonomic sympathetic nerves innervate peripheral resistance arteries, thereby regulating vascular tone and controlling blood supply to organs. Despite the fundamental importance of blood flow control, how sympathetic arterial innervation develops remains largely unknown. Here, we identified the axon guidance cue netrin-1 as an essential factor required for development of arterial innervation in mice. Netrin-1 was produced by arterial smooth muscle cells (SMCs) at the onset of innervation, and arterial innervation required the interaction of netrin-1 with its receptor, deleted in colorectal cancer (DCC), on sympathetic growth cones. Function-blocking approaches, including cell type-specific deletion of the genes encoding Ntn1 in SMCs and Dcc in sympathetic neurons, led to severe and selective reduction of sympathetic innervation and to defective vasoconstriction in resistance arteries. These findings indicate that netrin-1 and DCC are critical for the control of arterial innervation and blood flow regulation in peripheral organs.

Nerve growth factor decreases in sympathetic and sensory nerves of rats with chronic heart failure

Nerve growth factor (NGF) plays a critical role in the maintenance and survival of both sympathetic and sensory nerves. Also, NGF can regulate receptor expression and neuronal activity in the sympathetic and sensory neurons. Abnormalities in NGF regulation are observed in patients and animals with heart failure (HF). Nevertheless, the effects of chronic HF on the levels of NGF within the sympathetic and sensory nerves are not known. Thus, the ELISA method was used to assess the levels of NGF in the stellate ganglion (SG) and dorsal root ganglion (DRG) neurons of control rats and rats with chronic HF induced by myocardial infarction. Our data show for the first time that the levels of NGF were significantly decreased (P < 0.05) in the SG and DRG neurons 6-20 weeks after ligation of the coronary artery. In addition, a close relation was observed between the NGF levels and the left ventricular function. In conclusion, chronic HF impairs the expression of NGF in the sympathetic and sensory nerves. Given that sensory afferent nerves are engaged in the sympathetic nervous responses to somatic stimulation (i.e. muscle activity during exercise) via a reflex mechanism, our data indicate that NGF is likely responsible for the development of muscle reflex-mediated abnormal sympathetic responsiveness observed in chronic HF.

In vivo regulation of NGF-mediated functions by Nedd4-2 ubiquitination of TrkA

Trk neurotrophin receptor ubiquitination in response to ligand activation regulates signaling, trafficking, and degradation of the receptors. However, the in vivo consequences of Trk ubiquitination remain to be addressed. We have developed a mouse model with a mutation in the TrkA neurotrophin receptor (P782S) that results in reduced ubiquitination due to a lack of binding to the E3 ubiquitin ligase, Nedd4-2. In vivo analyses of TrkAP782S indicate that defective ubiquitination of the TrkA mutant results in an altered trafficking and degradation of the receptor that affects the survival of sensory neurons. The dorsal root ganglia from the TrkAP782S knock-in mice display an increased number of neurons expressing CGRP and substance P. Moreover, the mutant mice show enhanced sensitivity to thermal and inflammatory pain. Our results indicate that the ubiquitination of the TrkA neurotrophin receptor plays a critical role in NGF-mediated functions, such as neuronal survival and sensitivity to pain.

TrkA in vivo function is negatively regulated by ubiquitination

TrkA is a tyrosine kinase receptor required for development and survival of the peripheral nervous system. In the adult, TrkA and its ligand NGF are peripheral pain mediators, particularly in inflammatory pain states. However, how TrkA regulates the function of nociceptive neurons and whether its activity levels may lead to sensory abnormalities is still unclear. Here we report the characterization of a 3 aa (KFG) domain that negatively regulates TrkA level and function in response to NGF. Deletion of this domain in mouse causes a reduction of TrkA ubiquitination leading to an increase in TrkA protein levels and activity. The number of dorsal root ganglia neurons is not affected by the mutation. However, mutant mice have enhanced thermal sensitivity and inflammatory pain. Together, these data suggest that ubiquitination is a mechanism used in nociceptive neurons to regulate TrkA level and function. Our results may enhance our understanding of how ubiquitination affects TrkA activation following noxious thermal stimulation and inflammatory pain.

Signaling molecules and transcription factors involved in the development of the sympathetic nervous system, with special emphasis on the superior cervical ganglion

The cells that constitute the sympathetic nervous system originate from the neural crest. This review addresses the current understanding of sympathetic ganglion development viewed from molecular and morphological perspectives. Development of the sympathetic nervous system is categorized into three main steps, as follows: (1) differentiation and migration of cells in the neural crest lineage for formation of the primary sympathetic chain, (2) differentiation of sympathetic progenitors, and (3) growth and survival of sympathetic ganglia. The signaling molecules and transcription factors involved in each of these developmental stages are elaborated mostly on the basis of the results of targeted mutation of respective genes. Analyses in mutant mice revealed differences between the superior cervical ganglion (SCG) and the other posterior sympathetic ganglia. This review provides a summary of the similarities and differences in the development of the SCG and other posterior sympathetic ganglia. Relevant to the development of sympathetic ganglia is the demonstration that neuroendocrine cells, such as adrenal chromaffin cells and carotid body glomus cells, share a common origin with the sympathetic ganglia. Neural crest cells at the trunk level give rise to common sympathoadrenal progenitors of sympathetic neurons and chromaffin cells, while progenitors segregated from the SCG give rise to glomus cells. After separation from the sympathetic primordium, the progenitors of both chromaffin cells and glomus cells colonize the anlage of the adrenal gland and carotid body, respectively. This review highlights the biological properties of chromaffin cells and glomus cells, because, although both cell types are derivatives of sympathetic primordium, they are distinct in many respects.

Programmed cell death during neuronal development: the sympathetic neuron model

Developing sympathetic neurons of the superior cervical ganglion are one of the best studied models of neuronal apoptosis. These cells require nerve growth factor (NGF) for survival at the time that they innervate their final target tissues during late embryonic and early postnatal development. In the absence of NGF, developing sympathetic neurons die by apoptosis in a transcription-dependent manner. Molecular studies of sympathetic neuron apoptosis began in the 1980s. We now know that NGF withdrawal activates the mitochondrial (intrinsic) pathway of apoptosis in sympathetic neurons cultured in vitro, and the roles of caspases, Bcl-2 (B-cell CLL/lymphoma 2) family proteins and XIAP (X-linked inhibitor of apoptosis protein) have been extensively studied. Importantly, a considerable amount has also been learned about the intracellular signalling pathways and transcription factors that regulate programmed cell death in sympathetic neurons. In this article, we review the key papers published in the past few years, covering all aspects of apoptosis regulation in sympathetic neurons and focusing, in particular, on how signalling pathways and transcription factors regulate the cell death programme. We make some comparisons with other models of neuronal apoptosis and describe possible future directions for the field.

Peripheral nerve injury modulates neurotrophin signaling in the peripheral and central nervous system

Peripheral nerve injury disrupts the normal functions of sensory and motor neurons by damaging the integrity of axons and Schwann cells. In contrast to the central nervous system, the peripheral nervous system possesses a considerable capacity for regrowth, but regeneration is far from complete and functional recovery rarely returns to pre-injury levels. During development, the peripheral nervous system strongly depends upon trophic stimulation for neuronal differentiation, growth and maturation. The perhaps most important group of trophic substances in this context is the neurotrophins (NGF, BDNF, NT-3 and NT-4/5), which signal in a complex spatial and timely manner via the two structurally unrelated p75(NTR) and tropomyosin receptor kinase (TrkA, Trk-B and Trk-C) receptors. Damage to the adult peripheral nerves induces cellular mechanisms resembling those active during development, resulting in a rapid and robust increase in the synthesis of neurotrophins in neurons and Schwann cells, guiding and supporting regeneration. Furthermore, the injury induces neurotrophin-mediated changes in the dorsal root ganglia and in the spinal cord, which affect the modulation of afferent sensory signaling and eventually may contribute to the development of neuropathic pain. The focus of this review is on the expression patterns of neurotrophins and their receptors in neurons and glial cells of the peripheral nervous system and the spinal cord. Furthermore, injury-induced changes of expression patterns and the functional consequences in relation to axonal growth and remyelination as well as to neuropathic pain development will be reviewed.

SHP-2 deletion in postmigratory neural crest cells results in impaired cardiac sympathetic innervation

Autonomic innervation is an essential component of cardiovascular regulation that is first established from the neural crest (NC) lineage in utero and continues developing postnatally. Although in vitro studies have indicated that SH2-containing protein tyrosine phosphatase 2 (SHP-2) is a signaling factor critical for regulating sympathetic neuron differentiation, this has yet to be shown in the complex in vivo environment of cardiac autonomic innervation. Targeting SHP-2 within postmigratory NC lineages resulted in a fully penetrant mouse model of diminished sympathetic cardiac innervation and concomitant bradycardia. Immunohistochemistry of the sympathetic nerve marker tyrosine hydroxylase revealed a progressive loss of adrenergic ganglionic neurons and reduction of cardiac sympathetic axon density in Shp2 cKOs. Molecularly, Shp2 cKOs exhibit lineage-specific suppression of activated phospo-ERK1/2 signaling but not of other downstream targets of SHP-2 such as pAKT. Genetic restoration of the phosphorylated-extracellular signal-regulated kinase (pERK) deficiency via lineage-specific expression of constitutively active MEK1 was sufficient to rescue the sympathetic innervation deficit and its physiological consequences. These data indicate that SHP-2 signaling specifically through pERK in postmigratory NC lineages is essential for development and maintenance of sympathetic cardiac innervation postnatally.

Twins with hereditary sensory and autonomic neuropathy type IV with preserved periodontal sensation

Turkish twin brothers affected with hereditary sensory and autonomic neuropathy type IV (HSAN IV) are reported. Their clinical findings were generally typical for HSAN IV. Interestingly they both had preserved periodontal sensation. Mutation analysis of the NTRK1 gene showed a homozygous c.2001C>T substitution in exon 15 in both twins. This base substitution is predicted to change a polar, positively charged amino acid arginine to the highly active amino acid cystein at position 654 (p.Arg654Cys). The parents were heterozygous for the mutation. This mutation has been reported previously in one Japanese and one Arab patients. The preserved periodontal sensation has not previously been reported in patients affected with HSAN IV. This preserved sensation in our patients might have been through Ruffini endings, the periodontal mechanoreceptors which have been reported to be present in TrkA knockout mice. Here we report the first twins affected with HSAN IV and the observation that periodontal sensation is not affected by mutation in NTRK1.

Uncoupling of molecular maturation from peripheral target innervation in nociceptors expressing a chimeric TrkA/TrkC receptor

Neurotrophins and their receptors control a number of cellular processes, such as survival, gene expression and axonal growth, by activating multiple signalling pathways in peripheral neurons. Whether each of these pathways controls a distinct developmental process remains unknown. Here we describe a novel knock-in mouse model expressing a chimeric TrkA/TrkC (TrkAC) receptor from TrkA locus. In these mice, prospective nociceptors survived, segregated into appropriate peptidergic and nonpeptidergic subsets, projected normally to distinct laminae of the dorsal spinal cord, but displayed aberrant peripheral target innervation. This study provides the first in vivo evidence that intracellular parts of different Trk receptors are interchangeable to promote survival and maturation of nociceptors and shows that these developmental processes can be uncoupled from peripheral target innervation. Moreover, adult homozygous TrkAC knock-in mice displayed severe deficits in acute and tissue injury-induced pain, representing the first viable adult Trk mouse mutant with a pain phenotype.

Sensory neurons located in dorsal root ganglia are critical for perception of various stimuli by transmitting information from their peripheral targets to the spinal cord. During embryonic development, distinct populations of sensory neurons are defined based on expression of neurotrophin receptors Trks. Pain and temperature sensing neurons, or nociceptors, express NGF receptor TrkA, which control a number of diverse developmental processes, such as survival, gene expression and skin innervation. How these distinct processes are regulated by activation of same Trk receptor is currently unknown. Using a knock in approach, we generated a mouse with nociceptive neurons expressing a modified TrkA/TrkC receptor, which responds to NGF but signals through the intracellular part of another neurotrophin receptor, TrkC. Contrary to all previously reported NGF and TrkA mutants, these mice were viable and exhibited no obvious defects. Surprisingly, nociceptive neurons from these mice survived and matured normally, but failed to correctly innervate their peripheral target, skin. Thus, the intracellular parts of highly related receptors TrkA and TrkC are interchangeable for support of certain developmental processes but not others. Moreover, adult TrkA/TrkC mice exhibited drastic defects in pain sensation, making it an excellent model to study the role of NGF in nociception.

Neuronal signaling through endocytosis

The distinctive morphology of neurons, with complex dendritic arbors and extensive axons, presents spatial challenges for intracellular signal transduction. The endosomal system provides mechanisms that enable signaling molecules initiated by extracellular cues to be trafficked throughout the expanse of the neuron, allowing intracellular signals to be sustained over long distances. Therefore endosomes are critical for many aspects of neuronal signaling that regulate cell survival, axonal growth and guidance, dendritic branching, and cell migration. An intriguing characteristic of neuronal signal transduction is that endosomal trafficking enables physiological responses that vary based on the subcellular location of signal initiation. In this review, we will discuss the specialized mechanisms and the functional significance of endosomal signaling in neurons, both during normal development and in disease.

Establishment of neurovascular congruency in the mouse whisker system by an independent patterning mechanism

Nerves and vessels often run parallel to one another, a phenomenon that reflects their functional interdependency. Previous studies have suggested that neurovascular congruency in planar tissues such as skin is established through a "one-patterns-the-other" model, in which either the nervous system or the vascular system precedes developmentally and then instructs the other system to form using its established architecture as a template. Here, we find that, in tissues with complex three-dimensional structures such as the mouse whisker system, neurovascular congruency does not follow the previous model but rather is established via a mechanism in which nerves and vessels are patterned independently. Given the diversity of neurovascular structures in different tissues, guidance signals emanating from a central organizer in the specific target tissue may act as an important mechanism to establish neurovascular congruency patterns that facilitate unique target tissue function.

Cell biology in neuroscience: Death of developing neurons: new insights and implications for connectivity

The concept that target tissues determine the survival of neurons has inspired much of the thinking on neuronal development in vertebrates, not least because it is supported by decades of research on nerve growth factor (NGF) in the peripheral nervous system (PNS). Recent discoveries now help to understand why only some developing neurons selectively depend on NGF. They also indicate that the survival of most neurons in the central nervous system (CNS) is not simply regulated by single growth factors like in the PNS. Additionally, components of the cell death machinery have begun to be recognized as regulators of selective axonal degeneration and synaptic function, thus playing a critical role in wiring up the nervous system.

Modulation of neurotrophin signaling by monoclonal antibodies

The neurotrophin family is comprised of the structurally related secreted proteins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophine-4 (NT-4). They bind and activate the tyrosine kinase receptors Trk A, B, and C in a ligand-specific manner and additionally bind a shared p75NTR receptor. The neurotrophins were originally defined by their ability to support the survival and maturation of embryonic neurons. However, they also control important physiological functions of the adult nervous system including learning and memory, sensation, and energy homeostasis. For example, NGF/trkA signaling is critical for normal and pathological sensation of pain. Likewise, the BDNF/trkB pathway controls feeding and metabolism, and its dysfunction leads to severe obesity. Antibodies can modulate neurotrophin signaling. Thus, NGF blocking agents can attenuate pain in several animal models, and a recombinant humanized NGF blocking antibody (Tanezumab) has shown promising results in human clinical trials for osteoarthritic pain. On the other hand trkB agonist antibodies can modulate food intake and body weight in rodents and nonhuman primates. The power of monoclonal antibodies to modulate neurotrophin signaling promises to turn the rich biological insights into novel human medicines.

Nerve growth factor and nociception: from experimental embryology to new analgesic therapy

Nerve growth factor (NGF) is central to the development and functional regulation of sensory neurons that signal the first events that lead to pain. These sensory neurons, called nociceptors, require NGF in the early embryo to survive and also for their functional maturation. The long road from the discovery of NGF and its roles during development to the realization that NGF plays a major role in the pathophysiology of inflammatory pain will be reviewed. In particular, we will discuss the various signaling events initiated by NGF that lead to long-lasting thermal and mechanical hyperalgesia in animals and in man. It has been realized relatively recently that humanized function blocking antibodies directed against NGF show remarkably analgesic potency in human clinical trials for painful conditions as varied as osteoarthritis, lower back pain, and interstitial cystitis. Thus, anti-NGF medication has the potential to make a major impact on day-to-day chronic pain treatment in the near future. It is therefore all the more important to understand the precise pathways and mechanisms that are controlled by NGF to both initiate and sustain mechanical and thermal hyperalgesia. Recent work suggests that NGF-dependent regulation of the mechanosensory properties of sensory neurons that signal mechanical pain may open new mechanistic avenues to refine and exploit relevant molecular targets for novel analgesics.

Coronin-1 is a neurotrophin endosomal effector that is required for developmental competition for survival

Retrograde communication from axonal targets to neuronal cell bodies is critical for both the development and function of the nervous system. Much progress has been made in recent years linking long-distance, retrograde signaling to a signaling endosome, yet the mechanisms governing the trafficking and signaling of these endosomes remain mostly uncharacterized. Here we report that in mouse sympathetic neurons, the target-derived nerve growth factor (NGF)-tropomyosin-related kinase type 1 (TrkA, also called Ntrk1) signaling endosome, on arrival at the cell body, induces the expression and recruitment of a new effector protein known as Coronin-1 (also called Coro1a). In the absence of Coronin-1, the NGF-TrkA signaling endosome fuses to lysosomes sixfold to tenfold faster than when Coronin-1 is intact. We also define a new Coronin-1-dependent trafficking event in which signaling endosomes recycle and re-internalize on arrival at the cell body. Beyond influencing endosomal trafficking, Coronin-1 is also required for several NGF-TrkA-dependent signaling events, including calcium release, calcineurin activation and phosphorylation of cAMP responsive element binding protein (CREB). These results establish Coronin-1 as an essential component of a feedback loop that mediates NGF-TrkA endosome stability, recycling and signaling as a critical mechanism governing developmental competition for survival.

Neurotrophins in the regulation of cellular survival and death

The neurotrophins play crucial roles regulating survival and apoptosis in the developing and injured nervous system. The four neurotrophins exert profound and crucial survival effects on developing peripheral neurons, and their expression and action is intimately tied to successful innervation of peripheral targets. In the central nervous system, they are dispensable for neuronal survival during development but support neuronal survival after lesion or other forms of injury. Neurotrophins also regulate apoptosis of both peripheral and central neurons, and we now recognize that there are regulatory advantages to having the same molecules regulate life and death decisions. This chapter examines the biological contexts in which these events take place and highlights the specific ligands, receptors, and signaling mechanisms that allow them to occur.

Neurotrophin signalling and transcription programmes interactions in the development of somatosensory neurons

Somatosensory neurons of the dorsal root ganglia are generated from multipotent neural crest cells by a process of progressive specification and differentiation. Intrinsic transcription programmes active in somatosensory neuron progenitors and early post-mitotic neurons drive the cell-type expression of neurotrophin receptors. In turn, signalling by members of the neurotrophin family controls expression of transcription factors that regulate neuronal sub-type specification. This chapter explores the mechanisms by which this crosstalk between neurotrophin signalling and transcription programmes generates the diverse functional sub-types of somatosensory neurons found in the mature animal.

Pathogenic value of neuropeptides and growth factor proteins for the development of inflammation and itching in patients with prevalent dermatoses

Goal. To determine the value of neuropeptides and growth factor proteins for the development of inflammation and itching in patients with atopic dermatitis and psoriasis. Materials and methods. There was a study of 13 patients with atopic dermatitis, 28 patients with psoriasis and eleven healthy volunteers. The severity and prevalence of the skin lesion in patients with atopic dermatitis was compared using the SCORAD score, and in psoriatic patients — using the PASI index. The extent of itching was assessed using a visual analog scale. The level of neuropeptides in blood serum of the subjects was determined using the enzyme-linked immunoelectrodiffusion assay: substance P and calcitonin gene-related peptide as well as nerve growth factor, amphiregulin, an epidermal growth factor, and semaphorin 3A, a nerve repulsion factor. Results. A statistically significant increase in the level of nerve growth factors in blood serum of patients with atopic dermatitis was observed (91.37 ± 16.39 pg/mL) vs. the control group (10.68 ± 8.37 pg/mL) (p < 0.05) as well as increased level of amphiregulin (46.09 ± 5.22 pg/mL) vs. the control group (10.21 ± 2.10) (p < 0.05). A positive correlation between the level of the nerve growth factor and SCORAD score was revealed. Conclusion. The results obtained confirm that nerve growth factors and amphiregulin are involved in the pathogenesis of atopic dermatitis.

DRG axon elongation and growth cone collapse rate induced by Sema3A are differently dependent on NGF concentration

Regeneration of embryonic and adult dorsal root ganglion (DRG) sensory axons is highly impeded when they encounter neuronal growth cone-collapsing factor semaphorin3A (Sema3A). On the other hand, increasing evidence shows that DRG axon's regeneration can be stimulated by nerve growth factor (NGF). In this study, we aimed to evaluate whether increased NGF concentrations can counterweight Sema3A-induced inhibitory responses in 15-day-old mouse embryo (E15) DRG axons. The DRG explants were grown in Neurobasal-based medium with different NGF concentrations ranging from 0 to 100 ng/mL and then treated with Sema3A at constant 10 ng/mL concentration. To evaluate interplay between NGF and Sema3A number of DRG axons, axon outgrowth distance and collapse rate were measured. We found that the increased NGF concentrations abolish Sema3A-induced inhibitory effect on axon outgrowth, while they have no effect on Sema3A-induced collapse rate.

Pea3 transcription factor family members Etv4 and Etv5 mediate retrograde signaling and axonal growth of DRG sensory neurons in response to NGF

Nerve growth factor (NGF) is a target-derived neurotrophic growth factor that controls many aspects of sensory and sympathetic neuronal development. The identification of transcription factors and downstream target genes that mediate NGF-dependent neuronal differentiation and target field innervation is currently a major challenge. Here, we show that the Pea3 transcription factor family members Etv4 and Etv5 are expressed by developing TrkA-positive dorsal root ganglion (DRG) neurons during the period of target innervation. Real-time PCR assays indicated that Etv4 and Etv5 mRNAs are significantly induced by NGF in different neuronal cells, suggesting that they could be involved in the biological responses induced by this neurotrophin. Interestingly, distal axon application of NGF in compartmentalized cultures of rat DRG sensory neurons was sufficient to induce a significant increase in Etv4 and Etv5 mRNA expression. Pharmacological assays also revealed that activation of MEK/ERK (MAPK) pathway is required for Etv4 and Etv5 gene induction in response to NGF. Downregulation of Etv4 and Etv5 using small interference RNA knockdown experiments inhibited NGF-induced neurite outgrowth of rat sensory neurons, while overexpression of full-length Etv4 or Etv5 potentiated neuronal differentiation in response to this neurotrophin. Together, these data establish Etv4 and Etv5 as essential molecules of the transcriptional program linking neurotrophin signaling to sensory neuronal differentiation, and suggest that they can be involved in NGF-mediated target innervation.

Autonomic neural control of intrathoracic airways

Autonomic neural control of the intrathoracic airways aids in optimizing air flow and gas exchange. In addition, and perhaps more importantly, the autonomic nervous system contributes to host defense of the respiratory tract. These functions are accomplished by tightly regulating airway caliber, blood flow, and secretions. Although both the sympathetic and parasympathetic branches of the autonomic nervous system innervate the airways, it is the later that dominates, especially with respect to control of airway smooth muscle and secretions. Parasympathetic tone in the airways is regulated by reflex activity often initiated by activation of airway stretch receptors and polymodal nociceptors. This review discusses the preganglionic, ganglionic, and postganglionic mechanisms of airway autonomic innervation. Additionally, it provides a brief overview of how dysregulation of the airway autonomic nervous system may contribute to respiratory diseases.

Sympathetic denervation of peri-infarct myocardium requires the p75 neurotrophin receptor

Development of cardiac sympathetic heterogeneity after myocardial infarction contributes to ventricular arrhythmias and sudden cardiac death. Regions of sympathetic hyperinnervation and denervation appear in the viable myocardium beyond the infarcted area. While elevated nerve growth factor (NGF) is implicated in sympathetic hyperinnervation, the mechanisms underlying denervation are unknown. Recent studies show that selective activation of the p75 neurotrophin receptor (p75(NTR)) in sympathetic neurons causes axon degeneration. We used mice that lack p75(NTR) to test the hypothesis that activation of p75(NTR) causes peri-infarct sympathetic denervation after cardiac ischemia-reperfusion. Wild type hearts exhibited sympathetic denervation adjacent to the infarct 24h and 3 days after ischemia-reperfusion, but no peri-infarct sympathetic denervation occurred in p75(NTR)-/- mice. Sympathetic hyperinnervation was found in the distal peri-infarct myocardium in both genotypes 3 days after MI, and hyperinnervation was increased in the p75(NTR)-/- mice. By 7 days after ischemia-reperfusion, cardiac sympathetic innervation density returned back to sham-operated levels in both genotypes, indicating that axonal pruning did not require p75(NTR). Prior studies revealed that proNGF is elevated in the damaged left ventricle after ischemia-reperfusion, as is mRNA encoding brain-derived neurotrophic factor (BDNF). ProNGF and BDNF preferentially bind p75(NTR) rather than TrkA on sympathetic neurons. Immunohistochemistry using Bdnf-HA mice confirmed the presence of BDNF or proBDNF in the infarct after ischemia-reperfusion. Thus, at least two p75(NTR) ligands are elevated in the left ventricle after ischemia-reperfusion where they may stimulate p75(NTR)-dependent denervation of peri-infarct myocardium. In contrast, NGF-induced sympathetic hyperinnervation in the distal peri-infarct ventricle is attenuated by p75(NTR).

Heart development and regeneration via cellular interaction and reprogramming

The heart consists of many types of cells, including cardiomyocytes, vascular cells, neural cells, and cardiac fibroblasts. Adult cardiomyocytes are terminally differentiated cells, and loss of cardiomyocytes as a result of heart damage is irreversible. To regenerate damaged hearts and restore cardiac function, understanding the cellular and molecular basis of heart development is of considerable importance. Although it is well known that heart function is tightly regulated by cell-cell interactions, their roles in heart development are not clear. Recent studies, including ours, identified important roles of cell-cell interactions in heart development and function. The balance between neural chemoattractants and chemorepellents secreted from cardiomyocytes determines cardiac nervous development. Nerve growth factor is a potent chemoattractant synthesized by cardiomyocytes, whereas Sema3a is a neural chemorepellent expressed specifically in the subendocardium. Disruption of this molecular balance induces disorganized cardiac innervation and may lead to sudden cardiac death due to lethal arrhythmias. Cardiac fibroblasts, of which there are large populations in the heart, secrete high levels of specific extracellular matrix and growth factors. Embryonic cardiac fibroblast-specific secreted factors collaboratively promote mitotic activity of embryonic cardiomyocytes and expansion of ventricular chambers during cardiogenesis. More recently, utilizing knowledge of the regulatory mechanisms of heart development, we found that cardiac fibroblasts can be directly reprogrammed into cardiomyocyte-like cells in vitro and in vivo by gene transfer of cardiac-specific transcription factors. Understanding the mechanisms of heart development and cardiac reprogramming technology may provide new therapeutic approaches for heart disease in the future.

New and developing drugs for the treatment of neuropathic pain in diabetes

A number of agents from diverse pharmacological classes are used to treat neuropathic pain associated with diabetic peripheral neuropathy. Only three of these have regulatory approval for this indication in the U.S. In this focused article, I will discuss selected drugs, newly approved or in development, to treat neuropathic pain in patients with diabetic neuropathy. These will include agonists and antagonists of the transient receptor potential channels, a family of receptor proteins that play a role in the transduction of physical stress; sodium channel isoform specific antagonists; a recently approved dual-action opioid receptor agonist-norepinephrine reuptake inhibitor; gene therapy for neuropathic pain; and anti-nerve growth factor molecules. Mechanisms of action, preclinical supporting data, clinical trial evidence, and adverse effects will be reviewed.

Inhibition of endogenous NGF degradation induces mechanical allodynia and thermal hyperalgesia in rats

Background

We have previously shown a sprouting of sympathetic fibers into the upper dermis of the skin following subcutaneous injection of complete Freund’s adjuvant (CFA) into the hindpaw. This sprouting correlated with an increase in pain-related sensitivity. We hypothesized that this sprouting and pain-related behavior were caused by an increase in nerve growth factor (NGF) levels. In this study, we investigated whether the inhibition of mature NGF degradation, using a matrix metalloproteinase 2 and 9 (MMP-2/9) inhibitor, was sufficient to reproduce a similar phenotype.

Results

Behavioral tests performed on male Sprague–Dawley rats at 1, 3, 7 and 14 days after intra-plantar MMP-2/9 inhibitor administration demonstrated that acute and chronic injections of the MMP-2/9 inhibitor induced sensitization, in a dose dependent manner, to mechanical, hot and cold stimuli as measured by von Frey filaments, Hargreaves and acetone tests, respectively. Moreover, the protein levels of mature NGF (mNGF) were increased, whereas the levels and enzymatic activity of matrix metalloproteinase 9 were reduced in the glabrous skin of the hind paw. MMP-2/9 inhibition also led to a robust sprouting of sympathetic fibers into the upper dermis but there were no changes in the density of peptidergic nociceptive afferents.

Conclusions

These findings indicate that localized MMP-2/9 inhibition provokes a pattern of sensitization and fiber sprouting comparable to that previously obtained following CFA injection. Accordingly, the modulation of endogenous NGF levels should be considered as a potential therapeutic target for the management of inflammatory pain associated with arthritis.

Smad-interacting protein 1 affects acute and tonic, but not chronic pain

BACKGROUND

Smad-interacting protein 1 (also named Zeb2 and Zfhx1b) is a transcription factor that plays an important role in neuronal development and, when mutated, causes Mowat-Wilson syndrome (MWS). A corresponding mouse model carrying a heterozygous Zeb2 deletion was comprehensively analysed in the German Mouse Clinic. The most prominent phenotype was the reduced pain sensitivity. In this study, we investigated the role of Zeb2 in inflammatory and neuropathic pain.

METHODS

For this, we tested mutant Zeb2 animals in different models of inflammatory pain like abdominal constriction, formalin and carrageenan test. Furthermore, we studied the pain reactivity of the mice after peripheral nerve ligation. To examine the nociceptive transmission of primary sensory dorsal root ganglia (DRG) neurons, we determined the neuronal activity in the spinal dorsal horn after the formalin test using staining of c-Fos. Next, we characterized the neuronal cell population in the DRGs and in the sciatic nerve to study the effect of the Zeb2 mutation on peripheral nerve morphology.

RESULTS

The present data show that Zeb2 is involved in the development of primary sensory DRG neurons, especially of C- and Aδ fibres. These alterations contribute to a hypoalgesic phenotype in inflammatory but not in neuropathic pain in these Zeb2(+/-) mice.

CONCLUSION

Our data suggest that the under-reaction to pain observed in MWS patients results from a reduced responsivity to nociceptive stimulation rather than an inability to communicate discomfort.

Axon guidance of sympathetic neurons to cardiomyocytes by glial cell line-derived neurotrophic factor (GDNF)

Molecular signaling of cardiac autonomic innervation is an unresolved issue. Here, we show that glial cell line-derived neurotrophic factor (GDNF) promotes cardiac sympathetic innervation in vitro and in vivo. In vitro, ventricular myocytes (VMs) and sympathetic neurons (SNs) isolated from neonatal rat ventricles and superior cervical ganglia were cultured at a close distance. Then, morphological and functional coupling between SNs and VMs was assessed in response to GDNF (10 ng/ml) or nerve growth factor (50 ng/ml). As a result, fractions of neurofilament-M-positive axons and synapsin-I-positive area over the surface of VMs were markedly increased with GDNF by 9-fold and 25-fold, respectively, compared to control without neurotrophic factors. Pre- and post-synaptic stimulation of β₁-adrenergic receptors (BAR) with nicotine and noradrenaline, respectively, resulted in an increase of the spontaneous beating rate of VMs co-cultured with SNs in the presence of GDNF. GDNF overexpressing VMs by adenovirus vector (AdGDNF-VMs) attracted more axons from SNs compared with mock-transfected VMs. In vivo, axon outgrowth toward the denervated myocardium in adult rat hearts after cryoinjury was also enhanced significantly by adenovirus-mediated GDNF overexpression. GDNF acts as a potent chemoattractant for sympathetic innervation of ventricular myocytes, and is a promising molecular target for regulation of cardiac function in diseased hearts.

Chemotherapy-induced bone marrow nerve injury impairs hematopoietic regeneration

Anti-cancer chemotherapy drugs challenge hematopoietic tissues to regenerate, but commonly produce long-term sequelae. Deficits in hematopoietic stem or stromal cell function have been described, but the mechanisms mediating chemotherapy-induced hematopoietic dysfunction remain unclear. Administration of multiple cycles of cisplatin chemotherapy causes significant sensory neuropathy. Here, we demonstrate that chemotherapy-induced nerve injury in the bone marrow is a critical lesion impairing hematopoietic regeneration. We show using various pharmacological and genetic models that the selective loss of adrenergic innervation in the BM alters its regeneration following genotoxic insult. Sympathetic nerves in the marrow promote the survival of stem cell niche constituents that initiate recovery. Neuroprotection by deletion of Trp53 in sympathetic neurons or neuro-regeneration using 4-methylcatechol or glial-derived neurotrophic factor (GDNF) administration can restore hematopoietic recovery. Thus, these results shed light on the potential benefit of adrenergic nerve protection to shield hematopoietic niches from injury.

A sympathetic neuron autonomous role for Egr3-mediated gene regulation in dendrite morphogenesis and target tissue innervation

Egr3 is a nerve growth factor (NGF)-induced transcriptional regulator that is essential for normal sympathetic nervous system development. Mice lacking Egr3 in the germline have sympathetic target tissue innervation abnormalities and physiologic sympathetic dysfunction similar to humans with dysautonomia. However, since Egr3 is widely expressed and has pleiotropic function, it has not been clear whether it has a role within sympathetic neurons and if so, what target genes it regulates to facilitate target tissue innervation. Here, we show that Egr3 expression within sympathetic neurons is required for their normal innervation since isolated sympathetic neurons lacking Egr3 have neurite outgrowth abnormalities when treated with NGF and mice with sympathetic neuron-restricted Egr3 ablation have target tissue innervation abnormalities similar to mice lacking Egr3 in all tissues. Microarray analysis performed on sympathetic neurons identified many target genes deregulated in the absence of Egr3, with some of the most significantly deregulated genes having roles in axonogenesis, dendritogenesis, and axon guidance. Using a novel genetic technique to visualize axons and dendrites in a subpopulation of randomly labeled sympathetic neurons, we found that Egr3 has an essential role in regulating sympathetic neuron dendrite morphology and terminal axon branching, but not in regulating sympathetic axon guidance to their targets. Together, these results indicate that Egr3 has a sympathetic neuron autonomous role in sympathetic nervous system development that involves modulating downstream target genes affecting the outgrowth and branching of sympathetic neuron dendrites and axons.

The transcription factor Hmx1 and growth factor receptor activities control sympathetic neurons diversification

The sympathetic nervous system relies on distinct populations of neurons that use noradrenaline or acetylcholine as neurotransmitter. We show that fating of the sympathetic lineage at early stages results in hybrid precursors from which, genetic cell-lineage tracing reveals, all types progressively emerge by principal mechanisms of maintenance, repression and induction of phenotypes. The homeobox transcription factor HMX1 represses Tlx3 and Ret, induces TrkA and maintains tyrosine hydroxylase (Th) expression in precursors, thus driving segregation of the noradrenergic sympathetic fate. Cholinergic sympathetic neurons develop through cross-regulatory interactions between TRKC and RET in precursors, which lead to Hmx1 repression and sustained Tlx3 expression, thereby resulting in failure of TrkA induction and loss of maintenance of Th expression. Our results provide direct evidence for a model in which diversification of noradrenergic and cholinergic sympathetic neurons is based on a principle of cross-repressive functions in which the specific cell fates are directed by an active suppression of the expression of transcription factors and receptors that direct the alternative fate.

Specific paucity of unmyelinated C-fibers in cutaneous peripheral nerves of the African naked-mole rat: comparative analysis using six species of Bathyergidae

In mammalian peripheral nerves, unmyelinated C-fibers usually outnumber myelinated A-fibers. By using transmission electron microscopy, we recently showed that the saphenous nerve of the naked mole-rat (Heterocephalus glaber) has a C-fiber deficit manifested as a substantially lower C:A-fiber ratio compared with other mammals. Here we determined the uniqueness of this C-fiber deficit by performing a quantitative anatomical analysis of several peripheral nerves in five further members of the Bathyergidae mole-rat family: silvery (Heliophobius argenteocinereus), giant (Fukomys mechowii), Damaraland (Fukomys damarensis), Mashona (Fukomys darlingi), and Natal (Cryptomys hottentotus natalensis) mole-rats. In the largely cutaneous saphenous and sural nerves, the naked mole-rat had the lowest C:A-fiber ratio (∼1.5:1 compared with ∼3:1), whereas, in nerves innervating both skin and muscle (common peroneal and tibial) or just muscle (lateral/medial gastrocnemius), this pattern was mostly absent. We asked whether lack of hair follicles alone accounts for the C-fiber paucity by using as a model a mouse that loses virtually all its hair as a consequence of conditional deletion of the β-catenin gene in the skin. These β-catenin loss-of function mice (β-cat LOF mice) displayed only a mild decrease in C:A-fiber ratio compared with wild-type mice (4.42 compared with 3.81). We suggest that the selective cutaneous C-fiber deficit in the cutaneous nerves of naked mole-rats is unlikely to be due primarily to lack of skin hair follicles. Possible mechanisms contributing to this unique peripheral nerve anatomy are discussed.

Immunosympathectomy as the first phenotypic knockout with antibodies

In a PNAS Classic Article published in 1960, Rita Levi-Montalcini offered formal and conclusive proof that endogenous NGF was responsible for the survival of sympathetic neurons in vivo. Thus ended an experimental tour de force lasting a decade, starting with the demonstration that a humoral factor, produced from a tumor transplanted in a chicken embryo, was responsible for stimulating outgrowth of nerve fibers from sympathetic and sensory neurons. From a more general methodological point of view, this work provided a breakthrough in the quest to achieve targeted loss of function and experimentally validate the function of biological molecules. Finally, this work provided an example of the ablation of a specific neuronal subpopulation in an otherwise intact nervous system, an immunological knife of unsurpassed effectiveness and precision. The novelty and the importance of the PNAS Classic Article is discussed here, collocating it within the context of the particular moment of the NGF discovery saga, of Rita Levi-Montalcini's scientific and academic career, and of the general scientific context of those years. This seminal work, involving the use of antibodies for phenotypic knockout in vivo, planted seeds that were to bear new fruit many years later with the advent of monoclonal antibodies and recombinant antibody technologies.

Nerve growth factor-mediated regulation of pain signalling and proposed new intervention strategies in clinical pain management

Nerve growth factor (NGF) is the founding member of the neurotrophins family of proteins. It was discovered more than half a century ago through its ability to promote sensory and sympathetic neuronal survival and axonal growth during the development of the peripheral nervous system, and is the paradigmatic target-derived neurotrophic factor on which the neurotrophic hypothesis is based. Since that time, NGF has also been shown to play a key role in the generation of acute and chronic pain and in hyperalgesia in diverse pain states. NGF is expressed at high levels in damaged or inflamed tissues and facilitates pain transmission by nociceptive neurons through a variety of mechanisms. Genetic mutations in NGF or its tyrosine kinase receptor TrkA, lead to a congenital insensitivity or a decreased ability of humans to perceive pain. The hereditary sensory autonomic neuropathies (HSANs) encompass a spectrum of neuropathies that affect one's ability to perceive sensation. HSAN type IV and HSAN type V are caused by mutations in TrkA and NGF respectively. This review will focus firstly on the biology of NGF and its role in pain modulation. We will review neuropathies and clinical presentations that result from the disruption of NGF signalling in HSAN type IV and HSAN type V and review current advances in developing anti-NGF therapy for the clinical management of pain.

GDNF, NGF and BDNF as therapeutic options for neurodegeneration

Glial cell-derived neurotrophic factor (GDNF), and the neurotrophin nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are important for the survival, maintenance and regeneration of specific neuronal populations in the adult brain. Depletion of these neurotrophic factors has been linked with disease pathology and symptoms, and replacement strategies are considered as potential therapeutics for neurodegenerative diseases such as Parkinson's, Alzheimer's and Huntington's diseases. GDNF administration has recently been shown to be an effective treatment for Parkinson's disease, with clinical trials currently in progress. Trials with NGF for Alzheimer's disease are ongoing, with some degree of success. Preclinical results using BDNF also show much promise, although there are accompanying difficulties. Ultimately, the administration of a therapy involving proteins in the brain has inherent problems. Because of the blood-brain-barrier, the protein must be infused directly, produced by viral constructs, secreted from implanted protein-secreting cells or actively transported across the brain. An alternative to this is the use of a small molecule agonist, a modulator or enhancer targeting the associated receptors. We evaluate these neurotrophic factors as potential short or long-term treatments, weighing up preclinical and clinical results with the possible effects on the underlying neurodegenerative process.

Loss of NGF-TrkA signaling from the CNS is not sufficient to induce cognitive impairments in young adult or intermediate-aged mice

Many molecules expressed in the CNS contribute to cognitive functions either by modulating neuronal activity or by mediating neuronal trophic support and/or connectivity. An ongoing discussion is whether signaling of nerve growth factor (NGF) through its high-affinity receptor TrkA contributes to attention behavior and/or learning and memory, based on its expression in relevant regions of the CNS such as the hippocampus, cerebral cortex, amygdala and basal forebrain. Previous animal models carrying either a null allele or transgenic manipulation of Ngf or Trka have proved difficult in addressing this question. To overcome this problem, we conditionally deleted Ngf or Trka from the CNS. Our findings confirm that NGF-TrkA signaling supports survival of only a small proportion of cholinergic neurons during development; however, this signaling is not required for trophic support or connectivity of the remaining basal forebrain cholinergic neurons. Moreover, comprehensive behavioral analysis of young adult and intermediate-aged mice lacking NGF-TrkA signaling demonstrates that this signaling is dispensable for both attention behavior and various aspects of learning and memory.

ProNGF, a cytokine induced after myocardial infarction in humans, targets pericytes to promote microvascular damage and activation

proNGF and p75NTR are induced following fatal myocardial infraction and are required for the development of microvascular injury.

Treatment of acute cardiac ischemia focuses on reestablishment of blood flow in coronary arteries. However, impaired microvascular perfusion damages peri-infarct tissue, despite arterial patency. Identification of cytokines that induce microvascular dysfunction would provide new targets to limit microvascular damage. Pro–nerve growth factor (NGF), the precursor of NGF, is a well characterized cytokine in the brain induced by injury. ProNGF activates p75 neurotrophin receptor (p75^NTR) and sortilin receptors to mediate proapoptotic responses. We describe induction of proNGF by cardiomyocytes, and p75^NTR in human arterioles after fatal myocardial infarction, but not with unrelated pathologies. After mouse cardiac ischemia-reperfusion (I-R) injury, rapid up-regulation of proNGF by cardiomyocytes and p75^NTR by microvascular pericytes is observed. To identify proNGF actions, we generated a mouse expressing a mutant Ngf allele with impaired processing of proNGF to mature NGF. The proNGF-expressing mouse exhibits cardiac microvascular endothelial activation, a decrease in pericyte process length, and increased vascular permeability, leading to lethal cardiomyopathy in adulthood. Deletion of p75^NTR in proNGF-expressing mice rescues the phenotype, confirming the importance of p75^NTR-expressing pericytes in the development of microvascular injury. Furthermore, deficiency in p75^NTR limits infarct size after I-R. These studies identify novel, nonneuronal actions for proNGF and suggest that proNGF represents a new target to limit microvascular dysfunction.

Modern methods and approaches to studying the role of neurotransmitters in the pathogenesis of chronic inflammatory skin diseases accompanied with itching

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Emerging therapy for diabetic neuropathy: cell therapy targeting vessels and nerves

Diabetic neuropathy (DN), the most common complication of diabetes, frequently leads to foot ulcers and may progress to limb amputations. Despite continuous increase in incidence, there is no clinical therapy to effectively treat DN. Pathogenetically, DN is characterized by reduced vascularity in peripheral nerves and deficiency in angiogenic and neurotrophic factors. We will briefly review the pathogenetic mechanism of DN and address the effects and the mechanisms of cell therapies for DN. To reverse the changes of DN, studies have attempted to deliver neurotrophic or angiogenic factors for treatment in the form of protein or gene therapy; however, the effects turned out to be very modest if not ineffective. Recent studies have demonstrated that bone marrow (BM)-derived cells such as mononuclear cells or endothelial progenitor cells (EPCs) can effectively treat various cardiovascular diseases through their paracrine effects. As BM-derived cells include multiple angiogenic and neurotrophic cytokines, these cells were used for treating experimental DN and found to reverse manifestations of DN. Particularly, EPCs were shown to exert favorable therapeutic effects through enhanced neural neovascularization and neuro-protective effects. These findings clearly indicate that DN is a complex disorder with pathogenetic involvement of both vascular and neural components. Studies have shown that cell therapies targeting both vascular and neural elements are shown to be advantageous in treating DN.

Characterization of the expression and cell-surface localization of transmembrane protein 132A

Transmembrane protein 132A (TMEM132A, KIAA1583) was first isolated as a novel gene that is enriched during the embryonic and postnatal stages of rat brain development and interacts with GRP78. However, the biological functions of TMEM132A are scarcely characterized because the protein does not contain any known structural domains. Using a cell-surface biotinylation assay and immunocytochemical staining, we found that TMEM132A is a transmembrane glycoprotein consisting of a large extracellular domain in the N-terminal region and a small cytosolic domain in the C-terminal region. Partial deletions of the intracellular domain of TMEM132A had little effect on its expression level and cell-surface localization in transfected HEK293 cells, whereas deletions of the extracellular domain hampered transport to the cell surface. The expression pattern of each N-terminal mutant was immunocytochemically confirmed in HeLa cells transfected with the same constructs. Treatment with tunicamycin, an inhibitor of protein glycosylation, led to the accumulation of the unglycosylated form of TMEM132A in inverse proportion to the glycosylated form; however, both forms were localized at the cell surface at almost equal rates. In contrast, GRP78 overexpression led to the accumulation of unglycosylated TMEM132A, which was not detected on the cell surface. Inhibition of ER-Golgi transport by treatment with brefeldin A or the overexpression of mutant Sar1 attenuated the amount of cell-surface localized TMEM132A in HEK293 cells. Treatment with reagents disrupting intracellular calcium rapidly down-regulated the amount of TMEM132A protein in Neuro2a cells without affecting the expression level of its mRNA. Taken together, our data show that the novel cell-surface localized glycoprotein, TMEM132A, is regulated by several factors, including GRP78, Sar1, and intracellular calcium, in a post-transcriptional manner.