Prohormone Convertase Research Articles

Quantitative analysis of islet prohormone convertase 1/3 expression in human pancreas donors with diabetes.

Islet prohormone-processing enzymes convert peptide hormone precursors to mature hormones. Defective beta cell prohormone processing and the release of incompletely processed peptide hormones are observed prior to the onset of diabetes, yet molecular mechanisms underlying impaired prohormone processing during the development of diabetes remains largely unknown. Previous studies have shown that prohormone convertase 1/3 (PC1/3) protein and mRNA expression levels are reduced in whole islets from donors with type 1 diabetes, although whether PC1/3-mediated prohormone processing in alpha and beta cells is disrupted in type 1 diabetes remained to be explored. Herein, we aimed to analyse the expression of PC1/3 in islets from non-diabetic donors, autoantibody-positive donors and donors diagnosed with type 1 diabetes or type 2 diabetes. Immunostaining and high-dimensional image analysis were performed on pancreatic sections from a cross-sectional cohort of 54 donors obtained from the Network for Pancreatic Organ Donors with Diabetes (nPOD) repository, to evaluate PC1/3 expression patterns in islet alpha, beta and delta cells at different stages of diabetes. Alpha and beta cell morphology were altered in donors with type 1 diabetes, including decreased alpha and beta cell size. As expected, the insulin-positive and PC1/3-positive areas in the islets were both reduced, and this was accompanied by a reduced percentage of PC1/3-positive and insulin-positive/PC1/3-positive cells in islets. PC1/3 and insulin co-localisation was also reduced. The glucagon-positive area, as well as the percentage of glucagon-positive and glucagon-positive/PC1/3-positive cells in islets, was increased. PC1/3 and glucagon co-localisation was also increased in donors with type 1 diabetes. The somatostatin-positive cell area and somatostatin staining intensity were elevated in islets from donors with recent-onset type 1 diabetes. Our high-resolution histomorphological analysis of human pancreatic islets from donors with and without diabetes has uncovered details of the cellular origin of islet prohormone peptide processing defects. Reduced beta cell PC1/3 and increased alpha cell PC1/3 in islets from donors with type 1 diabetes pinpointed the functional deterioration of beta cells and the concomitant potential increase in PC1/3 usage for prohormone processing in alpha cells during the pathogenesis of type 1 diabetes. Our finding of PC1/3 loss in beta cells may inform the discovery of new prohormone biomarkers as indicators of beta cell dysfunction, and the finding of elevated PC1/3 expression in alpha cells may encourage the design of therapeutic targets via leveraging alpha cell adaptation in diabetes.

Ablation of PC1/3 in POMC-Expressing Tissues but Not in Immune Cells Induces Sepsis Hypersensitivity.

Prohormone convertase 1/3 (PC1/3) is an endopeptidase required for the processing of neuropeptide and endocrine peptide precursors; it is expressed in neuroendocrine tissues as well as in immune cells. In response to endotoxemia, global PC1/3 knockout mice mount a cytokine storm and die rapidly. Further, immune cells isolated from these mice have a pro-inflammatory signature, suggesting that PC1/3 activates an unknown anti-inflammatory peptide precursor in immune cells. Here, we tested this hypothesis using tissue-specific PC1/3 ablation models. Knocking out PC1/3 in the myeloid or the hematopoietic compartment did not induce any phenotype. In contrast, proopiomelanocortin (POMC)-specific PC1/3 knockout mice phenocopied global PC1/3 knockout mice, including an enlarged spleen size and a hyperinflammatory sepsis phenotype in response to mild endotoxemia. This phenotype was prevented by steroid therapy and mimicked by blocking corticoid receptors in wild-type mice. Thus, our data suggest that sepsis hypersensitivity in PC1/3 deficiency is uncoupled from immune cell intrinsic PC1/3 expression and is driven by a lack of anti-inflammatory glucocorticoids due to an impairment in the hypothalamic-pituitary-adrenal axis.

Fam3a-mediated prohormone convertase switch in α-cells regulates pancreatic GLP-1 production in an Nr4a2-Foxa2-dependent manner

BackgroundFam3a has been demonstrated to regulate pancreatic β-cell function and glucose homeostasis. However, the role and mechanism of Fam3a in regulating α-cell function remain unexplored. MethodsGlucagon and glucagon-like peptide-1 (GLP-1) levels in pancreas and plasma were measured in global Fam3a knockout (Fam3a−/−) mice. Human islet single-cell RNA sequencing (scRNA-seq) datasets were utilized to analyze gene expression correlations between FAM3A and PCSK1 (encoding PC1/3, which processes proglucagon into GLP-1). Mouse pancreatic α-cell line αTC1.9 cells were transfected with Fam3a siRNA or plasmid for Fam3a knockdown or overexpression to explore the effects of Fam3a on PC1/3 expression and GLP-1 production. The downstream mediator (including Nr4a2) was identified by transcriptomic analysis, and its role was confirmed by Fam3a knockdown or overexpression in αTC1.9 cells. Based on the interacted protein of Nr4a2 and the direct binding to Pcsk1 promoter, the transcription factor Foxa2 was selected for further verification. Nuclear translocation assay and dual-luciferase reporter assay were used to clarify the involvement of Fam3a-Nr4a2-Foxa2 pathway in PC1/3 expression and GLP-1 production. Moreover, α-cell-specific Fam3a knockout (Fam3aα−/−) mice were constructed to evaluate the metabolic variables and hormone levels under normoglycemic, high-fat diet (HFD)-fed and streptozotocin (STZ)-induced diabetic conditions. Exendin 9–39 (Ex9), a GLP-1 receptor antagonist, was used to investigate GLP-1 paracrine effects in Fam3aα−/− mice and in their primary islets. ResultsCompared with wild-type mice, pancreatic and plasma active GLP-1 levels were increased in Fam3a−/− mice. Analysis of human islet scRNA-seq datasets showed a significant negative correction between FAM3A and PCSK1 in α-cells. Fam3a knockdown upregulated PC1/3 expression and GLP-1 production in αTC1.9 cells, while Fam3a overexpression displayed inverse effects. Transcriptomic analysis identified Nr4a2 as a key downstream mediator of Fam3a, and Nr4a2 expression in αTC1.9 cells was downregulated and upregulated by Fam3a knockdown and overexpression, respectively. Nr4a2 silencing increased PC1/3 expression, albeit Nr4a2 did not directly bind to Pcsk1 promoter. Instead, Nr4a2 formed a complex with Foxa2 to facilitate Fam3a-mediated Foxa2 nuclear translocation. Foxa2 negatively regulated PC1/3 expression and GLP-1 production. Besides, Foxa2 inhibited the transcriptional activity of Pcsk1 promoter at specific binding sites 10 and 6, and this inhibition was intensified by Nr4a2 in αTC1.9 cells. Compared with Flox/cre littermates, improved glucose tolerance, increased active GLP-1 level in pancreas and plasma, upregulated plasma insulin level in response to glucose, and decreased plasma glucagon level were observed in Fam3aα−/− mice. Primary islets isolated from Fam3aα−/− mice also showed an increase in active GLP-1 and insulin release. In addition, the insulinotropic effect of intra-islet GLP-1 was blocked by Ex9 in Fam3aα−/− mice and in their primary islets. Similarly, HFD-fed Fam3aα−/− mice also exhibited an improved glucose tolerance. Both HFD-fed and STZ-induced diabetic Fam3aα−/− mice showed an increased pancreatic active GLP-1 level, an elevated plasma insulin level and a reduced plasma glucagon level. ConclusionsFam3a deficiency in α-cells enhances pancreatic GLP-1 production to improve β-cell function via paracrine signaling in an Nr4a2-Foxa2-PC1/3-dependent manner. Our study unveils a novel strategy for reprogramming α-cell proglucagon processing output from glucagon to GLP-1 and deepen the understanding of crosstalk between α-cells and β-cells.

Endocrinopathy due to proproteinkovertase 1/3 deficiency: primary enteropathy, diabetes insipidus, secondary hypothyroidism

Proprotein convertase 1/3 (PC1/3) deficiency is an autosomal recessive disease caused by rare mutations in the proprotein convertase subtilisin/kexin type 1 (PCSK 1)gene, associated with severe malabsorptive diarrhea, obesity and some endocrine abnormalities. Proprotein convertase 1/3 is acalcium-dependent serine endoprotease involved in the proteolytic processing of various prohormones (peptide hormones in enteroendocrine cells that are necessary for the absorption of nutrients and is also expressed in the arcuate and paraventricular nuclei of the hypothalamus, in the beta cells of the pancreas) in their bioactive forms. The onset of the disease in the neonatal period of life is characterized by aclinical picture of severe malabsorption diarrhea, accompanied by developmental delays, and requires long-term parenteral nutrition. As the disease progresses, additional endocrine abnormalities develop, including diabetes insipidus, growth hormone deficiency, primary hypogonadism, adrenal insufficiency, hypothyroidism, and obesity. We conducted aprospective observation of apatient with agenetic disease due to proprotein convertase 1/3 deficiency confirmed during follow-up. The patient was examined and treated at the State Novosibirsk Regional Clinical Hospital in Novosibirsk for 11 months, with repeated (3-fold) hospitalizations. Purpose: to demonstrate the features of the onset and course of the disease, as well as the difficulties in verifying the clinical diagnosis of an ultra-rare genetic disease from the category of endocrinopathies, the complexity of medical support and therapy. Apeculiarity of this case is the fact that the identified mutation in the gene was not previously registered in control Russian samples of the genetic mutation of proprotein convertase 1/3 deficiency, as well as apreviously undescribed variant of the nucleotide sequence in exon 4 of the PCSK1 gene in aheterozygous state and was not registered in control samples gnomAD and RUSeq. Proprotein convertase 1/3 deficiency is adisease that is amultidisciplinary problem, since etiopathogenetic therapy has not yet been developed. The disease has achronic course with constant relapses of intestinal syndrome, is difficult to manage with symptomatic treatments and, as it progresses, has ahigh risk of developing additional endocrinopathies and death. All of the above emphasizes the need for early diagnosis and selection of rational replacement and accompanying therapy to save the lives of patients.

A Controversy Regarding the Identity of the Enzyme That Mediates Glucagon-Like Peptide 1 Synthesis in Human Alpha Cells.

Processing of proglucagon into glucagon-like peptide-1 (GLP-1) and GLP-2 in intestinal L cells is mediated by the prohormone convertase 1/3 (PC1/3) while PC2 is responsible for the synthesis of glucagon in pancreatic alpha cells. While GLP-1 is also produced by alpha cells, the identity of the convertase involved in its synthesis is still unsettled. It also remains to be determined whether all alpha cells produce the incretin. The aims of this study were first, to elucidate the identity of the proconvertase responsible for GLP-1 production in human alpha cells, and second, to ascertain whether the number of glucagon cells expressing GLP-1 increase during diabetes. To answer these questions, sections of pancreas from donors' non-diabetic controls, type 1 and type 2 diabetes were processed for double-labelled immunostaining of glucagon and GLP-1 and of each hormone and either PC1 or PC2. Stained sections were examined by confocal microscopy. It was found that all alpha cells of islets from those three groups expressed GLP-1 and PC2 but not PC1/3. This observation supports the view that PC2 is the convertase involved in GLP-1 synthesis in all human glucagon cells and suggests that the regulation of its activity may have important clinical application in diabetes.

Understanding negative feedback: Changes in high-molecular-weight adrenocorticotropic hormone in adrenocorticotropic hormone-independent Cushing's syndrome.

Cushing's syndrome is characterized by chronic glucocorticoid oversecretion and diverse clinical manifestations. Distinguishing between adrenocorticotropic hormone (ACTH)-independent and ACTH-dependent forms is crucial for determining treatment options. Plasma ACTH levels aid in the differential diagnosis, with undetectable or low levels suggesting ACTH-independent hypercortisolemia. ACTH is derived from pro-opiomelanocortin, and its processing involves prohormone convertase 1/3. High-molecular-weight ACTH is generally found in ACTH-producing pituitary tumors and ectopic ACTH syndrome. The mechanism of negative feedback and the process of high-molecular-weight ACTH alternation during ACTH-independent Cushing's syndrome remain unclear. A 40-year-old woman with hypertension and multiple fractures developed symptoms suggestive of Cushing's syndrome. Computed tomography revealed a left adrenocortical tumor along with atrophy of the right adrenal gland. ACTH levels were undetectable at the previous clinic, indicating ACTH-independent Cushing's syndrome. However, subsequent measurements at our hospital revealed non-suppressed ACTH (18.1 pg/mL), prompting further investigation. Gel exclusion chromatography confirmed the presence of high-molecular-weight ACTH. Metyrapone treatment decreased the cortisol levels. In this situation, in which ACTH levels should be elevated, a decrease in high-molecular-weight ACTH levels was observed. Histological findings revealed cortisol-producing adenoma without ACTH expression. This case highlights the importance of assay differences in evaluating ACTH concentrations and introduces a novel finding of circulating high-molecular-weight ACTH. The observed decline in high-molecular-weight ACTH levels suggests a potential time lag in the negative feedback within the hypothalamic-pituitary-adrenal axis exhibited by glucocorticoids. This temporal aspect of the regulation of ACTH-related molecules warrants further exploration to enhance our understanding of the hypothalamic-pituitary-adrenal axis feedback mechanism.

PCSK2 can be Useful in a Panel Approach to Distinguish Foregut and Midgut Neuroendocrine Tumors.

A number of immunohistochemical stains have been examined for utility in establishing the site of origin for metastatic well-differentiated neuroendocrine tumors (NETs). In the gastrointestinal (GI) tract, distinguishing metastatic duodenal NETs from jejunoileal and other GI NETs is important for clinical work-up, prognosis, and therapy. A recent study indicated that prohormone convertase 2 (PCSK2 or PC2) had broad expression in small intestine and appendiceal NETs. Because the study did not include duodenal NETs, we examined PCSK2 expression in duodenal and other GI NETs. GI NETs (n = 69) and 13 corresponding lymph node metastases from stomach, duodenum, pancreas, ileum, appendix, and rectum were evaluated for the expression of PCSK2, along with ISL1, NKX2.2, CDX2, SATB2, and PAX8. Expression of each stain was evaluated using the H-score system, and differences in expression by site were evaluated by the chi square test. PCSK2 was expressed at similar frequency in duodenal (50%), pancreatic (59%), and ileal NETs (40%). PCSK2 was infrequently expressed in stomach (0%), appendiceal (8%), and rectal (25%) NETs. However, incorporating PCSK2 into a panel including ISL1, NKX2.2, CDX2, and SATB2 allowed development of an algorithm which had 87% sensitivity and 93% specificity for classification of ileal NETs; and 68% sensitivity and 98% specificity for pancreaticoduodenal NETs. In contrast to previous findings, PCSK2 does not show specificity for any particular GI site. An algorithmic approach incorporating the expression of PCSK2 with that of ISL1, NKX2.2, CDX2, and SATB2 is useful in discriminating pancreatic, duodenal, ileal, appendiceal, and rectal NETs.

Deciphering the dual nature of nesfatin-1: a tale of zinc ion’s Janus-faced influence

BackgroundNucleobindin-2 (Nucb2) and nesfatin-1 (N1) are widely distributed hormones that regulate numerous physiological processes, from energy homeostasis to carcinogenesis. However, the role of nesfatin-2 (N2), the second product of Nucb2 proteolytic processing, remains elusive. To elucidate the relationship between the structure and function of nesfatins, we investigated the properties of chicken and human homologs of N1, as well as a fragment of Nucb2 consisting of N1 and N2 conjoined in a head-to-tail manner (N1/2).ResultsOur findings indicate that Zn(II) sensing, in the case of N1, is conserved between chicken and human species. However, the data presented here reveal significant differences in the molecular features of the analyzed peptides, particularly in the presence of Zn(II). We demonstrated that Zn(II) has a Janus effect on the M30 region (a crucial anorexigenic core) of N1 and N1/2. In N1 homologs, Zn(II) binding results in the concealment of the M30 region driven by a disorder-to-order transition and adoption of the amyloid fold. In contrast, in N1/2 molecules, Zn(II) binding causes the exposure of the M30 region and its destabilization, resulting in strong exposure of the region recognized by prohormone convertases within the N1/2 molecule.ConclusionsIn conclusion, we found that Zn(II) binding is conserved between chicken and human N1. However, despite the high homology of chicken and human N1, their interaction modes with Zn(II) appear to differ. Furthermore, Zn(II) binding might be essential for regulating the function of nesfatins by spatiotemporally hindering the N1 anorexigenic M30 core and concomitantly facilitating N1 release from Nucb2.

Granulocyte pro-myeloperoxidase is redundantly processed by proprotein convertase furin and PC7 in HL-60 cells.

Neutrophil myeloperoxidase/H2O2/chloride system is a key mechanism to control pathogen infection. This enzyme, myeloperoxidase, plays a pivotal role in the arsenal of azurophilic granules that are released through degranulation upon neutrophil activation, which trigger local hypochlorous acid production. Myeloperoxidase gene encodes a protein precursor named promyeloperoxidase that arbors a propeptide that gets cleaved later during secretory routing in post-endoplasmic reticulum compartments. Although evidence suggested that this processing event was performed by one or different enzymes from the proprotein convertases family, the identity of this enzyme was never investigated. In this work, the naturally producing myeloperoxidase promyelocytic cell line HL-60 was used to investigate promyeloperoxidase cleavage during granulocytic differentiation in response to proprotein convertase inhibitors decanoyl-RVKR-chloromethylketone and hexa-d-arginine. Stable PC knockdown of endogenously expressed proprotein convertases, furin and PC7, was achieved using lentiviral delivery of shRNAs. None of the knockdown cell line could reproduce the effect of the pan-proprotein convertases inhibitor decanoyl-RVKR-chloromethylketone that accumulated intracellular promyeloperoxidase stores in HL-60 cells, therefore illustrating that both furin and PC7 redundantly process this proprotein.

Inhibition of proprotein convertases activity results in repressed stemness and invasiveness of cancer stem cells in gastric cancer.

Gastric cancer (GC), the fourth leading cause of cancer-related death worldwide, with most deaths caused by advanced and metastatic disease, has limited curative options. Here, we revealed the importance of proprotein convertases (PCs) in the malignant and metastatic potential of GC cells through the regulation of the YAP/TAZ/TEAD pathway and epithelial-to-mesenchymal transition (EMT) in cancer stem cells (CSC). The general PCs inhibitor, decanoyl-RVKR-chloromethyl-ketone (CMK), was used to repress PCs activity in CSCs of various GC cell lines. Their tumorigenic properties, drug resistance, YAP/TAZ/TEAD pathway activity, and invasive properties were then investigated in vitro, and their metastatic properties were explored in a mouse xenograft model. The prognostic value of PCs in GC patients was also explored in molecular databases of GC. Inhibition of PCs activity in CSCs in all GC cell lines reduced tumorsphere formation and growth, drug efflux, EMT phenotype, and invasive properties that are associated with repressed YAP/TAZ/TEAD pathway activity in vitro. In vivo, PCs' inhibition in GC cells reduced their metastatic spread. Molecular analysis of tumors from GC patients has highlighted the prognostic value of PCs. PCs are overexpressed in GC and associated with poor prognosis. PCs are involved in the malignant and metastatic potential of CSCs via the regulation of EMT, the YAP/TAZ/TEAD oncogenic pathway, and their stemness and invasive properties. Their repression represents a new strategy to target CSCs and impair metastatic spreading in GC.

Non-cross-linking advanced glycation end products affect prohormone processing.

Advanced glycation end products (AGEs) are non-enzymatic post-translational modifications of amino acids and are associated with diabetic complications. One proposed pathomechanism is the impaired processing of AGE-modified proteins or peptides including prohormones. Two approaches were applied to investigate whether substrate modification with AGEs affects the processing of substrates like prohormones to the active hormones. First, we employed solid-phase peptide synthesis to generate unmodified as well as AGE-modified protease substrates. Activity of proteases towards these substrates was quantified. Second, we tested the effect of AGE-modified proinsulin on the processing to insulin. Proteases showed the expected activity towards the unmodified peptide substrates containing arginine or lysine at the C-terminal cleavage site. Indeed, modification with Nε-carboxymethyllysine (CML) or methylglyoxal-hydroimidazolone 1 (MG-H1) affected all proteases tested. Cysteine cathepsins displayed a reduction in activity by ∼50% towards CML and MG-H1 modified substrates. The specific proteases trypsin, proprotein convertases subtilisin-kexins (PCSKs) type proteases, and carboxypeptidase E (CPE) were completely inactive towards modified substrates. Proinsulin incubation with methylglyoxal at physiological concentrations for 24 h resulted in the formation of MG-modified proinsulin. The formation of insulin was reduced by up to 80% in a concentration-dependent manner. Here, we demonstrate the inhibitory effect of substrate-AGE modifications on proteases. The finding that PCSKs and CPE, which are essential for prohormone processing, are inactive towards modified substrates could point to a yet unrecognized pathomechanism resulting from AGE modification relevant for the etiopathogenesis of diabetes and the development of obesity.

Ghrelin mediated cardioprotection using in vitro models of oxidative stress

Ghrelin is commonly known as the ‘hunger hormone’ due to its role in stimulating food intake in humans. However, the roles of ghrelin extend beyond regulating hunger. Our aim was to investigate the ability of ghrelin to protect against hydrogen peroxide (H2O2), a reactive oxygen species commonly associated with cardiac injury. An in vitro model of oxidative stress was developed using H2O2 injured H9c2 cells. Despite lentiviral ghrelin overexpression, H9c2 cell viability and mitochondrial function were not protected following H2O2 injury. We found that H9c2 cells lack expression of the preproghrelin cleavage enzyme prohormone convertase 1 (encoded by PCSK1), required to convert ghrelin to its active form. In contrast, we found that primary rat cardiomyocytes do express PCSK1 and were protected from H2O2 injury by lentiviral ghrelin overexpression. In conclusion, we have shown that ghrelin expression can protect primary rat cardiomyocytes against H2O2, though this effect was not observed in other cell types tested.

Pea protein hydrolysate stimulates GLP-1 secretion in NCI-H716 cells via simultaneously activating the sensing receptors CaSR and PepT1.

Glucagon-like peptide-1 (GLP-1) plays a crucial role in regulating glucose homeostasis by stimulating insulin secretion and suppressing glucagon release. Our previous study observed that pea protein hydrolysate (PPH) exhibited the function of triggering GLP-1 secretion. However, the underlying mechanisms have not been revealed. Herein, the mechanisms of PPH-stimulated GLP-1 secretion were investigated in NCI-H716 cells. The PPH-induced GLP-1 secretion was reduced (p < 0.05) after adding the sensing receptor antagonists NPS-2143 and 4-AMBA, indicating that activation of both calcium-sensing receptor (CaSR) and peptide-transporter 1 (PepT1) was involved in PPH-triggered GLP-1 release. Moreover, the intracellular Ca2+ level increased by 2.01 times during the PPH-induced GLP-1 secretion. Similarly, the cAMP content also increased by 1.43 times after stimulation by PPH. The RT-qPCR results showed that PPH increased the gene expression of prohormone convertase 1/3 (PCSK-1) by 2.79-fold, which effectively promoted the conversion of proglucagon (GCG) to GLP-1. The specific pathway of PPH-induced GLP-1 secretion may involve both CaSR and PepT1 activation-induced Ca2+ influx and cAMP generation, which effectively enhanced the enzyme activity of prohormone convertase 1/3 (PCSK-1) and ultimately promoted GLP-1 secretion.

Diversity in Proprotein Convertase Reactivity among Human Papillomavirus Types.

The cleavage of viral surface proteins by furin is associated with some viruses' high virulence and infectivity. The human papillomavirus (HPV) requires the proteolytic processing of its capsid proteins for activation before entry. Variability in reactivity with furin and other proprotein convertases (PCs) among HPV types was investigated. HPV16, the most prevalent and carcinogenic HPV type, reacted with PCs with the broadest selectivity compared to other types in reactions of pseudoviral particles with the recombinant PCs, furin, PC4, PC5, PACE4, and PC7. Proteolytic preactivation was assessed using a well-established entry assay into PC-inhibited cells based on the green fluorescent protein as a reporter. The inhibition of the target cell PC activity with serpin-based PC-selective inhibitors also showed a diversity of PC selectivity among HPV types. HPV16 reacted with furin at the highest rate compared to the other types in time-dependent preactivation reactions and produced the highest entry values standardized to pseudoviral particle concentration. The predominant expression of furin in keratinocytes and the high reactivity of HPV16 with this enzyme highlight the importance of selectively targeting furin as a potential antiviral therapeutic approach.

Peak-agnostic high-resolution cis-regulatory circuitry mapping using single cell multiome data.

Single same cell RNAseq/ATACseq multiome data provide unparalleled potential to develop high resolution maps of the cell-type specific transcriptional regulatory circuitry underlying gene expression. We present CREMA, a framework that recovers the full cis-regulatory circuitry by modeling gene expression and chromatin activity in individual cells without peak-calling or cell type labeling constraints. We demonstrate that CREMA overcomes the limitations of existing methods that fail to identify about half of functional regulatory elements which are outside the called chromatin 'peaks'. These circuit sites outside called peaks are shown to be important cell type specific functional regulatory loci, sufficient to distinguish individual cell types. Analysis of mouse pituitary data identifies a Gata2-circuit for the gonadotrope-enriched disease-associated Pcsk1 gene, which is experimentally validated by reduced gonadotrope expression in a gonadotrope conditional Gata2-knockout model. We present a web accessible human immune cell regulatory circuit resource, and provide CREMA as an R package.

A group of pancreatic islet β cell‐like neurons are vulnerable to energy deficiency

AbstractBackgroundAlzheimer’s disease (AD) bear resemblance to the diabetes mellitus for that both of them exhibit beta‐amyloid (Aβ) deposition, insulin resistance and glycometabolic disorder. Peripheral islet β cells produce insulin and islet amyloid peptides, but whether there is a group of neurons in the brain like islet β cells is not clear.MethodHybridize APP/PS1 transgenic mice and CaMKII‐CreERT2/+ ;Tpkfl/fl strain, with tamoxifen induced Tpk knockout at 6 months of age, to form a model of energy deficiency. Labeling neuron and microglia with NeuN and Iba1 antibody, and immunofluorescence was used to observe Aβ, insulin‐like growth factor expression. TUNEL staining was applied to test cell apoptosis.ResultWe found that layer 5 cortical pyramidal neurons are strongly marked by Aβ antibody, 4G8, in APP/PS1 transgenic mice. Immunofluorescence showed that these 4G8‐positive neurons colocalized with insulin‐like growth factor 1/2 and highly expressed prohormone convertase 2. Further, we conditionally knocked out Tpk gene, a key gene involved in glucose metabolism, in excitatory neurons of APP/PS1 mice. Over time, NeuN and Iba1 labeling showed that the significant loss of neuron and activation of microglia happened in layer 5 cerebral cortex at the earliest. Additionally, the 4G8‐positive neurons in this layer were stained by TUNEL and markedly reduced in the early stage.ConclusionWe found a group of islet β cell‐like neurons that are vulnerable to glucose energy impairment, suggesting a group of vulnerable neurons in sporadic AD, and implicating the cytological mechanism of association between AD and diabetes.

Alphafold2-Assisted Structure-Function Analysis of Human Erythroferrone Relevant for Its Iron-Regulatory Function

Erythroferrone (ERFE), an erythrokine that helps mobilize iron for developing erythrocytes, acts by decreasing the production of hepcidin, through sequestration of bone morphogenetic proteins (BMPs) that bind to BMP receptors to activate hepcidin transcription. We used Alphafold2 (AF2) to model the conformation of human erythroferrone monomers and various multimers, with or without interactions with BMPs, with emphasis on the principal ligand, the BMP2/6 heterodimer. We then tested the models by targeted mutations to disrupt key interactions suggested by the models, and assessed the effect of the mutations on bioactivity and BMP binding. ERFE is a member of the C1q/TNFa family of proteins known for containing N-terminal unstructured regions and C-terminal TNFa-like globular heads that promote the formation of a spectrum of biologically significant multimers. After cleavage by a prohormone convertase, the ERFE molecule consists of an unstructured N-terminal segment residues 43-185 and a globular TNF-like head 186-354. We found that a segment of the N-terminal region of the molecule-segment 43-148 of the 354 amino acid protein-was sufficient to bind BMPs and suppress hepcidin; the larger C-terminal region does neither. For bioassays, we prepared ERFE or its mutants in HEK293 mammalian cells and tested these without purification, so as not to disrupt their mixture of multimeric conformations. The Hep3B human liver cell line was used for bioactivity assays with the readout of hepcidin mRNA concentrations, measured by qRT-PCR. To avoid the confounding effects of ERFE multimerization driven by the TNFa-like globular regions on avidity, we purified untagged ERFE N-terminal (43-148) segments or their mutants from bacteria, and measured the binding between these and BMPs using surface plasmon resonance. These forms lacked TNFa-like heads and, unlike full length ERFE, did not form multimers in nondenaturing PAGE. We identified and explored several structural elements within the ERFE N-terminus. All models of BMP interaction with ERFE predicted the binding of a tryptophan-containing hydrophobic helix of ERFE to a deep groove formed at the interface of all BMP dimers (BMP2/6 in cyan/green, ERFE in magenta; interaction in callout box, left panel). The highly evolutionarily conserved hydrophobic region (residues 81-86) was required for bioactivity and for tight binding to BMPs. Deletion of the hydrophobic segment or W82A substitution of the strictly conserved tryptophan ablated bioactivity and greatly decreased the binding of ERFE to BMPs. In nearly all models, a positively-charged cationic segment and the collagen-like segment made no contact with BMPs. However, the cationic segment was required for activity (right panel) although its deletion had only minor effect on binding to BMP. The specific arrangement of arginines and lysines in this segment did not matter for bioactivity or binding. We showed that the segment was essential for heparin-binding and propose that it may serve to concentrate ERFE at the site of its activity. Deletion of the collagen segment or the more distal helical segment (green) impaired IC 50 much less (50-100fold) but also substantially disrupted monomeric binding. The collagen segment forms a triple helix in trimeric models of ERFE, but the helix is disrupted by BMP binding. Secondary binding contacts between ERFE and BMPs in AF2 varied depending on the oligomeric state of erythroferrone. In monomers and dimers, the helical segment made contact with the contralateral wing of the BMP dimer. Remarkably, both primary and secondary binding interactions of BMPs were structurally similar to the BMP interactions with their receptors or known antagonists. Nondenaturing PAGE suggested that the predominant form of ERFE was a hexamer. The AF2 structure of hexameric ERFE (magenta) with three molecules of BMP2/6 (cyan-green) showed that each BMP heterodimer bound two ERFE proximal helical segments including 81-86, within each of its two BMP2/6 interfacial grooves (left panel) but unlike in monomers and dimers, the secondary interaction did not involve the distal helical segment but the globular heads (red trimers on each side). Despite their reductionist nature, these studies provide useful structural predictions that should allow better pharmacologic targeting of this important erythroid regulator of iron homeostasis.

Top-Down Proteomics of Mouse Islets With Beta Cell CPE Deletion Reveals Molecular Details in Prohormone Processing.

Altered prohormone processing, such as with proinsulin and pro-islet amyloid polypeptide (proIAPP), has been reported as an important feature of prediabetes and diabetes. Proinsulin processing includes removal of several C-terminal basic amino acids and is performed principally by the exopeptidase carboxypeptidase E (CPE), and mutations in CPE or other prohormone convertase enzymes (PC1/3 and PC2) result in hyperproinsulinemia. A comprehensive characterization of the forms and quantities of improperly processed insulin and other hormone products following Cpe deletion in pancreatic islets has yet to be attempted. In the present study we applied top-down proteomics to globally evaluate the numerous proteoforms of hormone processing intermediates in a β-cell-specific Cpe knockout mouse model. Increases in dibasic residue-containing proinsulin and other novel proteoforms of improperly processed proinsulin were found, and we could classify several processed proteoforms as novel substrates of CPE. Interestingly, some other known substrates of CPE remained unaffected despite its deletion, implying that paralogous processing enzymes such as carboxypeptidase D (CPD) can compensate for CPE loss and maintain near normal levels of hormone processing. In summary, our quantitative results from top-down proteomics of islets provide unique insights into the complexity of hormone processing products and the regulatory mechanisms.

Luminescent reporter cells enable the identification of broad-spectrum antivirals against emerging viruses.

The emerging viruses SARS-CoV-2 and arenaviruses cause severe respiratory and hemorrhagic diseases, respectively. The production of infectious particles of both viruses and virus spread in tissues requires cleavage of surface glycoproteins (GPs) by host proprotein convertases (PCs). SARS-CoV-2 and arenaviruses rely on GP cleavage by PCs furin and subtilisin kexin isozyme-1/site-1 protease (SKI-1/S1P), respectively. We report improved luciferase-based reporter cell lines, named luminescent inducible proprotein convertase reporter cells that we employ to monitor PC activity in its authentic subcellular compartment. Using these sensor lines we screened a small compound library in high-throughput manner. We identified 23 FDA-approved small molecules, among them monensin which displayed broad activity against furin and SKI-1/S1P. Monensin inhibited arenaviruses and SARS-CoV-2 in a dose-dependent manner. We observed a strong reduction in infectious particle release upon monensin treatment with little effect on released genome copies. This was reflected by inhibition of SARS-CoV-2 spike processing suggesting the release of immature particles. In a proof of concept experiment using human precision cut lung slices, monensin potently inhibited SARS-CoV-2 infection, evidenced by reduced infectious particle release. We propose that our PC sensor pipeline is a suitable tool to identify broad-spectrum antivirals with therapeutic potential to combat current and future emerging viruses.

An N terminomics toolbox combining 2-pyridinecarboxaldehyde probes and click chemistry for profiling protease specificity

Proteomic profiling of protease-generated N termini provides key insights into protease function and specificity. However, current technologies have sequence limitations or require specialized synthetic reagents for N-terminal peptide isolation. Here, we introduce an N terminomics toolbox that combines selective N-terminal biotinylation using 2-pyridinecarboxaldehyde (2PCA) reagents with chemically cleavable linkers to enable efficient enrichment of protein N termini. By incorporating a commercially available alkyne-modified 2PCA in combination with Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC), our strategy eliminates the need for chemical synthesis of N-terminal probes. Using these reagents, we developed PICS2 (Proteomic Identification of Cleavage Sites with 2PCA) to profile the specificity of subtilisin/kexin-type proprotein convertases (PCSKs). We also implemented CHOPPER (chemical enrichment of protease substrates with purchasable, elutable reagents) for global sequencing of apoptotic proteolytic cleavage sites. Based on their broad applicability and ease of implementation, PICS2 and CHOPPER are useful tools that will advance our understanding of protease biology.