Prohormone convertases in mouse submandibular gland: co-localization of furin and nerve growth factor

Obesity-linked circular RNA circTshz2-2 regulates the neuronal cell cycle and spatial memory in the brain

Metabolic syndromes, including obesity, cause neuropathophysiological changes in the brain, resulting in cognitive deficits. Only a few studies explored the contribution of non-coding genes in these pathophysiologies. Recently, we identified obesity-linked circular RNAs (circRNA) by analyzing the brain cortices of high-fat-fed obese mice. In this study, we scrutinized a conserved and neuron-specific circRNA, circTshz2-2, which affects neuronal cell cycle and spatial memory in the brain. Transcriptomic and cellular analysis indicated that circTshz2-2 dysregulation altered the expression of cell division-related genes and induced cell cycle arrest at the G2/M phase of the neuron. We found that circTshz2-2 bound to the YY1 transcriptional complex and suppressed Bdnf transcription. Suppression of circTshz2-2 increased BDNF expression and reduced G2/M checkpoint proteins such as Cyclin B2 and CDK1 through BDNF/TrkB signaling pathway, resulting in cell cycle arrest and neurite elongation. Inversely, overexpression of circTshz2-2 decreased BDNF expression, induced cell cycle proteins, and shortened the neurite length, indicating that circTshz2-2 regulates neuronal cell cycle and structure. Finally, we showed that circTshz2-2 affects spatial memory in wild-type and obese mice. Our data have revealed potential regulatory roles of obesity-related circTshz2-2 on the neuronal cell cycle and memory function providing a novel link between metabolic syndromes and cognitive deficits.

Extracellular and intracellular cleavages of proBDNF required at two distinct stages of late-phase LTP

Although late-phase long-term potentiation (L-LTP) is implicated in long-term memory, its molecular mechanisms are largely unknown. Here we provide evidence that L-LTP can be divided into two stages: an induction stage (I) and a maintenance stage (II). Both stages require mature brain-derived neurotrophic factor (mBDNF), but involve distinct underlying mechanisms. Stage I requires secretion of existing proBDNF followed by extracellular cleavage by tPA/plasmin. Stage II depends on newly synthesized BDNF. Surprisingly, mBDNF at stage II is derived from intracellular cleavage of proBDNF by furin/PC1. Moreover, stage I involves BDNF-TrkB signaling mainly through MAP kinase, whereas all three signaling pathways (phospholipase C-γ, PI3 kinase, and MAP kinase) are required for the maintenance of L-LTP at stage II. These results reveal the molecular basis for two temporally distinct stages in L-LTP, and provide insights on how BDNF modulates this long-lasting synaptic alternation at two critical time windows.

Temporospatially regulated expression of subtilisin-like proprotein convertase PACE4 (SPC4) during development of the rat submandibular gland

The temporospatial expression of PACE4, a member of the mammalian subtilisin-like proprotein convertase family involved in the activation of growth/differentiation factors, was investigated by in situ hybridization during the development of the rat submandibular gland (SMG). At the initiation stage (day 15.5 of gestation; E15), PACE4 was intensely expressed in the submandibular epithelium, but weakly expressed in the mesenchymal cells. At E16 when the branching morphogenesis becomes obvious, the expression of PACE4 in the mesenchyme was further decreased, although its level in the submandibular epithelium had not changed remarkably from that at E15. During the next stage of embryonic development (E17-E20), PACE4 was expressed in the cells derived from the submandibular epithelium, which include the proacinar, terminal tubular, and presumptive ductal cells. In the perinatal SMG, PACE4 was still expressed intensely in the terminal portion of the SMG containing the proacinar and terminal tubular cells, whereas its expression in the ductal cells was obviously decreased at the second postnatal day (P2) and at P6. Acinar cells expressing no PACE4 appeared, and their numbers increased following their development (P9-P20). At P30 when the PACE4 expression in the acinar cells was completely suppressed, its expression in the ductal cells became intense again. This temporospatially regulated expression of PACE4 suggests its apparent association with the proliferation, differentiation, and establishment of functional acinar and ductal cells of the SMG.

Processing of nerve growth factor: the role of basic amino acid clusters in the pro-region

Neurotrophins are synthesized first as precursors called pro-neurotrophins, and their propeptides are then proteolytically removed to form mature neurotrophins. However, a significant proportion of total neurotrophins has been shown to be secreted as pro-neurotrophins. Furthermore, pro- and mature neurotrophins have been shown to elicit opposite effects on cell survival. Thus, the processing step of neurotrophins is very important. In order to understand the mechanism of neurotrophin processing, we focused on the two basic amino acid clusters in the pro-region of nerve growth factor (NGF). Various NGFs mutated at basic amino acids in the pro-region were introduced in COS7 and PC12 cells. The results indicated that these basic amino acid clusters were actually cleaved in the cells by furin, but that their cleavage contributed little to the production of mature NGF. However, one of the two sites was considered to contribute to mature NGF production depending on conditions used.

Increased NGF proforms in aged sympathetic neurons and their targets

Target-derived neurotrophins such as nerve growth factor (NGF) and neurotrophin-3 (NT-3) regulate sympathetic neuron survival. Here, NGF and NT-3 protein and transcript were examined in sympathetic neurons and targets in order to determine their role in age-related neuronal atrophy. One obvious alteration was a dramatic increase (up to 50-fold) in NGF protein forms, corresponding to proNGF-B, in the superior cervical ganglion (SCG) and targets where sympathetic innervation shows atrophy. In the iris, where sympathetic innervation is protected into old age, proNGF-B was decreased. Alterations in NGF transcript paralleled changes in NGF protein, albeit to a lesser degree. Though significantly increased in aged SCG, NT-3 protein, found primarily as the 'mature' form, showed only minor changes in most tissues, though NT-3 mRNA generally was decreased. In contrast, both NT-3 transcript and NT-3 precursors were increased in iris. The dramatic increases in proNGF, together with minimal changes in NT-3, suggest that alterations in NGF regulation may contribute to the loss of sympathetic innervation observed in many aged peripheral targets.

'Mature' nerve growth factor is a minor species in most peripheral tissues

The classic neurotrophin hypothesis is based on the idea that innervating neurons derive 'mature' neurotrophin provided by the target for their survival. Yet large precursor forms of the neurotrophin nerve growth factor (NGF) have been reported in both central and peripheral tissues. In the present study, immunoblotting was used to survey peripheral tissues containing NGF-responsive neurons and to characterize various NGF species. These results demonstrate that 'mature' forms of NGF, i.e., the 13 and 16kDa species, are rare in sympathetic and sensory ganglia and in their peripheral targets, and that large molecular weight NGF precursors are abundant. In addition, certain NGF forms predominate in a given tissue, with each tissue exhibiting a characteristic NGF expression pattern. These findings suggest that NGF processing in peripheral tissues and in NGF-responsive ganglia may involve a variety of NGF species.

Early days of the nerve growth factor proteins

Adult male mouse submaxillary glands served as the preferred starting material for the isolation of the nerve growth factor (NGF) proteins in most of the isolation studies done. Two types of NGF proteins were isolated from extracts of the gland, a high-molecular-weight 7S NGF complex and a low-molecular-weight protein variously called NGF, betaNGF, or 2.5S NGF. The latter, which mediated all known biological functions of NGF, were closely related forms of a basic NGF dimer in which the N and C termini of two monomers (chains) were modified by proteolytic enzymes to different extents with no effect on biological activity. The betaNGF dimer showed a novel protein structure in which the two chains interacted non-covalently over a wide surface. Correspondingly, the betaNGF dimer was found to be unusually stable and the form through which NGFs actions were mediated at physiological concentrations. The betaNGF dimer was one of three subunits in 7S NGF; the other two were the gamma subunit, an arginine esteropeptidase or kallikrein, and the alpha subunit, an inactive kallikrein. Two zinc ions were also present in the complex and contributed greatly to its stability. There was much debate about whether 7S NGF was a specific protein complex of interacting subunits and, if so, what functions it might play in the biology of NGF. Observations of the inhibition of the enzyme activity of the gamma subunit and of the biological activity of betaNGF in 7S NGF were important in determining that 7S NGF was a naturally occurring complex and the sole source of NGF in the gland extract or in saliva. Specific interactions between the active site of the gamma subunit and the C-terminal arginine residues of the NGF chains, confirmed in the three-dimensional structure of 7S NGF, suggested a role for the gamma subunit in pro-NGF processing during the assembly of 7S NGF. In spite of the detailed knowledge of 7S NGF structure, no information on the role of this complex in the neurobiology of NGF has emerged. With the exception of the submaxillary gland of an African rodent, no other source of NGF has been convincingly shown to synthesize the alpha and gamma subunits, and they may well be irrelevant to NGFs actions.

Nerve growth factor expression in parasympathetic neurons: regulation by sympathetic innervation

Interactions between sympathetic and parasympathetic nerves are important in regulating visceral target function. Sympathetic nerves are closely apposed to, and form functional synapses with, parasympathetic axons in many effector organs. The molecular mechanisms responsible for these structural and functional interactions are unknown. We explored the possibility that Nerve Growth Factor (NGF) synthesis by parasympathetic neurons provides a mechanism by which sympathetic-parasympathetic interactions are established. Parasympathetic pterygopalatine ganglia NGF-gene expression was examined by in situ hybridization and protein content assessed by immunohistochemistry. Under control conditions, NGF mRNA was present in approximately 60% and NGF protein was in 40% of pterygopalatine parasympathetic neurons. Peripheral parasympathetic axons identified by vesicular acetylcholine transporter-immunoreactivity also displayed NGF immunoreactivity. To determine if sympathetic innervation regulates parasympathetic NGF expression, the ipsilateral superior cervical ganglion was excised. Thirty days postsympathectomy, the numbers of NGF mRNA-positive neurons were decreased to 38% and NGF immunoreactive neurons to 15%. This reduction was due to a loss of sympathetic nerve impulse activity, as similar reductions were achieved when superior cervical ganglia were deprived of preganglionic afferent input for 40 days. These findings provide evidence that normally NGF is synthesized by parasympathetic neurons and transported anterogradely to fibre terminals, where it may be available to sympathetic axons. Parasympathetic NGF expression, in turn, is augmented by impulse activity within (and presumably transmitter release from) sympathetic axons. It is suggested that parasympathetic NGF synthesis and its modulation by sympathetic innervation provides a molecular basis for establishment and maintenance of autonomic axo-axonal synaptic interactions.

Rodent submandibular gland peptide hormones and other biologically active peptides

The cervical sympathetic trunk-submandibular gland neuroendocrine axis plays an integral role in physiological adaptations and contributes to the maintenance of systemic homeostasis, particularly under the 'stress conditions' seen with tissue damage, inflammation, and aggressive behavior. The variety of polypeptides, whose release from acinar and ductal cells is under sympathetic nervous system control, offers coordinated and progressive levels of endocrine communication. Proteolytic enzymes (e.g. the kallikreins and furin maturases) are involved in the conversion of inactive precursors (e. g. Pro-EGF and SMR1) into biologically active molecules (e.g. EGF, SMR1-pentapeptide), which act on local or distant targets and thereby modulate the homeostatic process.

Characterization of nerve growth factor precursor protein expression by human prostate stromal cells: a role in selective neurotrophin stimulation of prostate epithelial cell growth

BACKGROUND

Nerve growth factor (NGF) immunoreactive proteins derived from human prostatic stromal cells (hPS) have been implicated in the paracrine regulation of prostate epithelial cell growth. However, mature NGFbeta does not appear to be expressed by these cells. In order to determine whether NGF precursors are expressed by these cells, we investigated the potential processing and expression of precursor forms of NGF by human prostatic stromal cells, and examined the effects of NGF precursor moieties along with the other members of the neurotrophin family of gene products on soft agar colony formation of prostate epithelial cells.

METHODS

Specific antibodies to the peptide domains defined as N4 and L38, and the NGFbeta moiety of prepro-NGF, were used in immunoblot assays to characterize the molecular weight forms of precursor NGF secreted by human prostatic stromal cells. The potential processing of NGF precursors with two enzymes, NGFgamma and trypsin, was performed by incubation with stromal cell secretory protein containing precursor NGF. The selective effects of the N4, L38, and NGFbeta peptide domains of precursor NGF, along with the remaining members of the neurotrophin family, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5), were examined for their ability to stimulate growth of prostate tumor epithelial cells in an assay of soft agar colony formation.

RESULTS

Immunoblot analysis of stromal cell secretory protein identified NGF precursors of 35 kDa and 27 kDa, along with the partially processed 22-kDa form of pro-NGF, whereas mature NGFbeta was not observed. Treatment of precursor NGF with NGFgamma and trypsin did not produce the large intermediate forms of pro-NGF, although these two enzymes did appear to cleave the N-terminal peptide from NGFbeta. Of the N4, L38, and NGFbeta peptide domains of precursor NGF, only NGFbeta significantly stimulated the anchorage-independent growth of TSU-pr1 prostate epithelial cells in soft agar. The other members of the neurotrophin family of gene products had no effect on the anchorage-independent growth of prostate tumor cells.

CONCLUSIONS

Human prostate stromal cells secrete the 35-kDa and 27-kDa precursor forms of NGF arising from alternate start sites, and the partially processed 22-kDa form of pro-NGF. Whereas the N4, L38, and NGFbeta peptide domains present within pro-NGF were previously shown to induce phosphorylation of the high-affinity NGF receptor, tropomyosin receptor kinase (Trk), only the NGFbeta moiety was able to stimulate anchorage-independent growth of prostate tumor cells. Likewise, the other neurotrophin family members did not stimulate anchorage-independent growth of prostate tumor cells. Hence, it would appear that NGF may be the predominant neurotrophic growth factor for prostate growth, albeit via precursor forms of NGF, and that its effect appears to be selectively mediated via the NGFbeta moiety of these NGF precursors.

Nerve growth factor and proprotein convertases furin and PC7 in transected sciatic nerves and in nerve segments cultured in conditioned media: their presence in Schwann cells, macrophages, and smooth muscle cells

Synthesis of proteins such as nerve growth factor (NGF) is induced after nerve lesion. The NGF precursor (pro-NGF) requires a posttranslational processing by proprotein convertases to become active. In this report, we re-examine the localization of NGF protein and mRNA in injured nerve and show that the candidate pro-NGF convertases furin and PC 7 colocalize with NGF in non-neuronal cells in nerve. By Northern blot analysis, 1.5-kb and 1.3-kb NGF mRNAs were shown to be increased in distal and immediately proximal nerve segments on days 1, 4, and 14 after lesion; by Western blot analysis, NGF proteins of high molecular weight were detected after injury. In vivo, two phases of NGF immunopositivity were observed, in macrophages and perivascular cells shortly after lesion and in endoneurial cells on day 1 and 4. To identify the cells containing NGF, nerve segments were incubated in serum-containing medium with or without conditioning by white blood cells isolated from the circulation. Both hybridization and immunoreactivity signals for NGF were elevated after incubation of nerve segments for 4 hours in conditioned media, so that cells with NGF immunoreactivity could be identified by antibodies to specific cell markers. In these nerve fragments, Schwann cells, perivascular smooth muscle cells, and macrophages contained NGF immunoreactivity. The concentration of furin and PC7 mRNA also increased in lesioned nerves. By immunocytochemical investigation of nerve explants, furin and PC7 were detected in endoneurial cells, macrophages and perivascular cells and were colocalized with NGF. These in vitro and in vivo findings suggest that both furin and PC7 are associated with NGF in several cell types of the sciatic nerve and, hence, may be implicated in intracellular processing of pro-NGF.

Attenuation of intestinal and cardiovascular anaphylaxis by the salivary gland tripeptide FEG and its D-isomeric analog feG

The effects of the submandibular gland peptide-T (SGP-T; Thr-Asp-Ile-Phe-Gly-Gly; TDIFEGG), its carboxy-terminal fragment (the tripeptide FEG; Phe-Glu-Gly), and the D-isomeric analog (feG) on intestinal and cardiovascular anaphylactic reactions were studied. The tripeptides, FEG and feG, when administered intravenously or orally to egg albumin-sensitized Hooded Lister or Sprague-Dawley rats 30 min prior to challenge with the antigen, totally prevented the disruption of intestinal motility and the development of anaphylaxis provoked diarrhea and inhibited anaphylactic hypotension by 66%. Submandibular gland peptides participate in the regulation of systemic inflammatory reactions, and the D-amino acid tripeptide, feG, is a potent, orally active anti-anaphylactic agent.