Mitochondrial-derived peptides: Antidiabetic functions and evolutionary perspectives

Mitochondrial-derived peptides (MDPs) are a novel class of bioactive microproteins encoded by short open-reading frames (sORF) in mitochondrial DNA (mtDNA). Currently, three types of MDPs have been identified: Humanin (HN), MOTS-c (Mitochondrial ORF within Twelve S rRNA type-c), and SHLP1-6 (small Humanin-like peptide, 1 to 6). The 12 S ribosomal RNA (MT-RNR1) gene harbors the sequence for MOTS-c, whereas HN and SHLP1-6 are encoded by the 16 S ribosomal RNA (MT-RNR2) gene. Special genetic codes are used in mtDNA as compared to nuclear DNA: (i) ATA and ATT are used as start codons in addition to the standard start codon ATG; (ii) AGA and AGG are used as stop codons instead of coding for arginine; (iii) the standard stop codon UGA is used to code for tryptophan. While HN, SHLP6, and MOTS-c are encoded by the H (heavy owing to high guanine + thymine base composition)-strand of the mtDNA, SHLP1-5 are encoded by the L (light owing to less guanine + thymine base composition)-strand. MDPs attenuate disease pathology including Type 1 diabetes (T1D), Type 2 diabetes (T2D), gestational diabetes, Alzheimer's disease (AD), cardiovascular diseases, prostate cancer, and macular degeneration. The current review will focus on the MDP regulation of T2D, T1D, and gestational diabetes along with an emphasis on the evolutionary pressures for conservation of the amino acid sequences of MDPs.

Direct Transorbital Approach for Treatment of Carotid Cavernous Fistula: An Illustrative Case Series

BACKGROUND AND OBJECTIVES

Endovascular techniques have become the first-line treatment for carotid-cavernous fistulas (CCFs). Direct transorbital venous access may be used if anatomic constraints limit standard transarterial or transvenous access. We describe our institutional experience with the transorbital approach for Barrow Type A-D CCFs.

METHODS

Patients with CCFs undergoing transorbital endovascular treatment at our institution between 2017 and 2019 were retrospectively reviewed. Demographic, treatment, and outcome data were collected.

RESULTS

Eight patients met inclusion criteria, 4 female and 4 male patients. The mean age was 43 years, with 6 right-sided CCF and 2 left-sided CCFs. Symptoms were present for an average of 1.5 months before treatment. All patients presented with eye pain and subjective visual changes. Seven (87.5%) patients presented with proptosis, 6 (75%) patients had elevated intraocular pressure (IOP), and 3 (37.5%) patients had ophthalmoplegia. Six CCFs (75%) were spontaneous, and 2 CCFs (25%) were traumatic. Barrow types were A (n = 1), B (n = 1), C (n = 1), and D (n = 5). All patients underwent direct percutaneous transorbital embolization with coils followed by Onyx. Three patients had undergone prior transarterial and/or transvenous treatment. A radiographic cure was obtained in all patients after direct transorbital embolization. After CCF cure, cranial nerve palsies resolved in 66.7% of patients, visual acuity in the affected eye was improved or stable in 75% of patients, and IOP had normalized in 85.7% of patients. Proptosis improved in all patients, with complete resolution in 75%.

CONCLUSION

Direct transorbital embolization is a safe and potentially curative treatment for all 4 Barrow types of CCFs.

Risk of Incident and Fatal Colorectal Cancer After Young-Onset Adenoma Diagnosis: A National Cohort Study

INTRODUCTION

Colorectal cancer (CRC) incidence and mortality rates are increasing in adults aged <50 years. Young-onset adenoma (YOA)-adenoma detected in adults younger than 50 years-may signify increased CRC risk, but this association has not been widely studied. Our aim was to compare the risk of incident and fatal CRC in adults aged <50 years with YOA diagnosis compared with those with a normal colonoscopy.

METHODS

We conducted a cohort study of US Veterans aged 18-49 years who received colonoscopy between 2005 and 2016. The primary exposure of interest was YOA. Primary outcomes included incident and fatal CRC. We used Kaplan-Meier curves to calculate cumulative incident and fatal CRC risk and Cox models to examine relative CRC risk.

RESULTS

The study cohort included 54,284 Veterans aged <50 years exposed to colonoscopy, among whom 13% (n = 7,233) had YOA at start of follow-up. Cumulative 10-year CRC incidence was 0.11% (95% confidence interval [CI]: 0.00%-0.27%) after any adenoma diagnosis, 0.18% (95% CI: 0.02%-0.53%) after advanced YOA diagnosis, 0.10% (95% CI: 0.00%-0.28%) after nonadvanced adenoma diagnosis, and 0.06% (95% CI: 0.02%-0.09%) after normal colonoscopy. Veterans with advanced adenoma had 8-fold greater incident CRC risk than those with normal colonoscopy (hazard ratio: 8.0; 95% CI: 1.8-35.6). Across groups, no differences in fatal CRC risk were observed.

DISCUSSION

Young-onset advanced adenoma diagnosis was associated with 8-fold increased incident CRC risk compared with normal colonoscopy. However, cumulative CRC incidence and mortality at 10 years among individuals with either young onset non-advanced or advanced adenoma diagnosis were both relatively low.

Baseline Characteristics and Longitudinal Outcomes of Traditional Serrated Adenomas: A Cohort Study

BACKGROUND AND AIMS

Traditional serrated adenomas (TSAs) may confer increased risk for colorectal cancer (CRC). Our objective with this study was to examine clinical characteristics and long-term outcomes associated with TSA diagnosis.

METHODS

We conducted a retrospective cohort study of U.S. Veterans ≥18 years of age with ≥1 TSA between 1999 and 2018. Baseline characteristics, colonoscopy findings, and diagnosis of incident and fatal CRC were abstracted. Advanced neoplasia was defined by CRC or adenoma with high-grade dysplasia, villous histology, or size ≥1 cm. Follow-up was through CRC diagnosis, death, or end of study (December 31, 2018).

RESULTS

A total of 853 Veterans with a baseline TSA were identified; 74% were ≥60 years of age, 96% were men, 14% were Black, and 73% were non-Hispanic White. About 64% were current or former smokers. Over 2044 total person-years at follow-up, there were 11 incident CRC cases and 1 CRC death. Cumulative CRC incidence was 1.34% (95% confidence interval [CI], 0.67%-2.68%), and cumulative CRC death was 0.12% (95% CI, 0.00%-0.35%). Among the subset of 378 TSA patients with ≥1 surveillance colonoscopy, 65.1% had high-risk neoplasia on follow-up. CRC incidence among TSA patients was significantly higher than in a comparison cohort of patients with normal baseline colonoscopy at baseline (hazard ratio, 3.70; 95% CI, 1.63-8.41) and similar to a comparison cohort with baseline conventional advanced adenoma (hazard ratio, 0.86; 95% CI, 0.45-1.64).

CONCLUSION

Individuals with TSA have substantial risk for CRC based on their cumulative CRC incidence, as well as significant risk of developing other high-risk neoplasia at follow-up surveillance colonoscopy. These data underscore importance of current recommendations for close colonoscopy surveillance after TSA diagnosis.

Catestatin: Antimicrobial Functions and Potential Therapeutics

The rapid increase in drug-resistant and multidrug-resistant infections poses a serious challenge to antimicrobial therapies, and has created a global health crisis. Since antimicrobial peptides (AMPs) have escaped bacterial resistance throughout evolution, AMPs are a category of potential alternatives for antibiotic-resistant "superbugs". The Chromogranin A (CgA)-derived peptide Catestatin (CST: hCgA_352-372; bCgA_344-364) was initially identified in 1997 as an acute nicotinic-cholinergic antagonist. Subsequently, CST was established as a pleiotropic hormone. In 2005, it was reported that N-terminal 15 amino acids of bovine CST (bCST_1-15 aka cateslytin) exert antibacterial, antifungal, and antiyeast effects without showing any hemolytic effects. In 2017, D-bCST_1-15 (where L-amino acids were changed to D-amino acids) was shown to exert very effective antimicrobial effects against various bacterial strains. Beyond antimicrobial effects, D-bCST_1-15 potentiated (additive/synergistic) antibacterial effects of cefotaxime, amoxicillin, and methicillin. Furthermore, D-bCST_1-15 neither triggered bacterial resistance nor elicited cytokine release. The present review will highlight the antimicrobial effects of CST, bCST_1-15 (aka cateslytin), D-bCST_1-15, and human variants of CST (Gly364Ser-CST and Pro370Leu-CST); evolutionary conservation of CST in mammals; and their potential as a therapy for antibiotic-resistant "superbugs".

Immunosuppression of Macrophages Underlies the Cardioprotective Effects of CST (Catestatin)

[Figure: see text].

Catestatin regulates vesicular quanta through modulation of cholinergic and peptidergic (PACAPergic) stimulation in PC12 cells

We have previously shown that the chromogranin A (CgA)-derived peptide catestatin (CST: hCgA_352-372) inhibits nicotine-induced secretion of catecholamines from the adrenal medulla and chromaffin cells. In the present study, we seek to determine whether CST regulates dense core (DC) vesicle (DCV) quanta (catecholamine and chromogranin/secretogranin proteins) during acute (0.5-h treatment) or chronic (24-h treatment) cholinergic (nicotine) or peptidergic (PACAP, pituitary adenylyl cyclase activating polypeptide) stimulation of PC12 cells. In acute experiments, we found that both nicotine (60 μM) and PACAP (0.1 μM) decreased intracellular norepinephrine (NE) content and increased ³H-NE secretion, with both effects markedly inhibited by co-treatment with CST (2 μM). In chronic experiments, we found that nicotine and PACAP both reduced DCV and DC diameters and that this effect was likewise prevented by CST. Nicotine or CST alone increased expression of CgA protein and together elicited an additional increase in CgA protein, implying that nicotine and CST utilize separate signaling pathways to activate CgA expression. In contrast, PACAP increased expression of CgB and SgII proteins, with a further potentiation by CST. CST augmented the expression of tyrosine hydroxylase (TH) but did not increase intracellular NE levels, presumably due to its inability to cause post-translational activation of TH through serine phosphorylation. Co-treatment of CST with nicotine or PACAP increased quantal size, plausibly due to increased synthesis of CgA, CgB and SgII by CST. We conclude that CST regulates DCV quanta by acutely inhibiting catecholamine secretion and chronically increasing expression of CgA after nicotinic stimulation and CgB and SgII after PACAPergic stimulation.

Catestatin Inhibits Obesity-Induced Macrophage Infiltration and Inflammation in the Liver and Suppresses Hepatic Glucose Production, Leading to Improved Insulin Sensitivity

The activation of Kupffer cells (KCs) and monocyte-derived recruited macrophages (McMΦs) in the liver contributes to obesity-induced insulin resistance and type 2 diabetes. Mice with diet-induced obesity (DIO mice) treated with chromogranin A peptide catestatin (CST) showed several positive results. These included decreased hepatic/plasma lipids and plasma insulin, diminished expression of gluconeogenic genes, attenuated expression of proinflammatory genes, increased expression of anti-inflammatory genes in McMΦs, and inhibition of the infiltration of McMΦs resulting in improvement of insulin sensitivity. Systemic CST knockout (CST-KO) mice on normal chow diet (NCD) ate more food, gained weight, and displayed elevated blood glucose and insulin levels. Supplementation of CST normalized glucose and insulin levels. To verify that the CST deficiency caused macrophages to be very proinflammatory in CST-KO NCD mice and produced glucose intolerance, we tested the effects of (sorted with FACS) F4/80⁺Ly6C^- cells (representing KCs) and F4/80^-Ly6C⁺ cells (representing McMΦs) on hepatic glucose production (HGP). Both basal HGP and glucagon-induced HGP were markedly increased in hepatocytes cocultured with KCs and McMΦs from NCD-fed CST-KO mice, and the effect was abrogated upon pretreatment of CST-KO macrophages with CST. Thus, we provide a novel mechanism of HGP suppression through CST-mediated inhibition of macrophage infiltration and function.

Astrocyte-Specific Deletion of Peroxisome-Proliferator Activated Receptor-γ Impairs Glucose Metabolism and Estrous Cycling in Female Mice

Mice lacking peroxisome-proliferator activated receptor-γ (PPARγ) in neurons do not become leptin resistant when placed on a high-fat diet (HFD). In male mice, this results in decreased food intake and increased energy expenditure, causing reduced body weight, but this difference in body weight is not observed in female mice. In addition, estrous cycles are disturbed and the ovaries present with hemorrhagic follicles. We observed that PPARγ was more highly expressed in astrocytes than neurons, so we created an inducible, conditional knockout of PPARγ in astrocytes (AKO). The AKO mice had impaired glucose tolerance and hepatic steatosis that did not worsen with HFD. Expression of gluconeogenic genes was elevated in the mouse livers, as was expression of several genes involved in lipogenesis, lipid transport, and storage. The AKO mice also had a reproductive phenotype with fewer estrous cycles, elevated plasma testosterone levels, reduced corpora lutea formation, and alterations in hypothalamic and ovarian gene expression. Thus, the phenotypes of the AKO mice were very different from those seen in the neuronal knockout mice, suggesting distinct roles for PPARγ in these two cell types.

Chromogranin A regulates vesicle storage and mitochondrial dynamics to influence insulin secretion

Chromogranin A (CgA) is a prohormone and a granulogenic factor that regulates secretory pathways in neuroendocrine tissues. In β-cells of the endocrine pancreas, CgA is a major cargo in insulin secretory vesicles. The impact of CgA deficiency on the formation and exocytosis of insulin vesicles is yet to be investigated. In addition, no literature exists on the impact of CgA on mitochondrial function in β-cells. Using three different antibodies, we demonstrate that CgA is processed to vasostatin- and catestatin-containing fragments in pancreatic islet cells. CgA deficiency in Chga-KO islets leads to compensatory overexpression of chromogranin B, secretogranin II, SNARE proteins and insulin genes, as well as increased insulin protein content. Ultrastructural studies of pancreatic islets revealed that Chga-KO β-cells contain fewer immature secretory granules than wild-type (WT) control but increased numbers of mature secretory granules and plasma membrane-docked vesicles. Compared to WT control, CgA-deficient β-cells exhibited increases in mitochondrial volume, numerical densities and fusion, as well as increased expression of nuclear encoded genes (Ndufa9, Ndufs8, Cyc1 and Atp5o). These changes in secretory vesicles and the mitochondria likely contribute to the increased glucose-stimulated insulin secretion observed in Chga-KO mice. We conclude that CgA is an important regulator for coordination of mitochondrial dynamics, secretory vesicular quanta and GSIS for optimal secretory functioning of β-cells, suggesting a strong, CgA-dependent positive link between mitochondrial fusion and GSIS.

Muscle injury, impaired muscle function and insulin resistance in Chromogranin A-knockout mice

Chromogranin A (CgA) is widely expressed in endocrine and neuroendocrine tissues as well as in the central nervous system. We observed CgA expression (mRNA and protein) in the gastrocnemius (GAS) muscle and found that performance of CgA-deficient Chga-KO mice in treadmill exercise was impaired. Supplementation with CgA in Chga-KO mice restored exercise ability suggesting a novel role for endogenous CgA in skeletal muscle function. Chga-KO mice display (i) lack of exercise-induced stimulation of pAKT, pTBC1D1 and phospho-p38 kinase signaling, (ii) loss of GAS muscle mass, (iii) extensive formation of tubular aggregates (TA), (iv) disorganized cristae architecture in mitochondria, (v) increased expression of the inflammatory cytokines Tnfα, Il6 and Ifnγ, and fibrosis. The impaired maximum running speed and endurance in the treadmill exercise in Chga-KO mice correlated with decreased glucose uptake and glycolysis, defects in glucose oxidation and decreased mitochondrial cytochrome C oxidase activity. The lack of adaptation to endurance training correlated with the lack of stimulation of p38MAPK that is known to mediate the response to tissue damage. As CgA sorts proteins to the regulated secretory pathway, we speculate that lack of CgA could cause misfolding of membrane proteins inducing aggregation of sarcoplasmic reticulum (SR) membranes and formation of tubular aggregates that is observed in Chga-KO mice. In conclusion, CgA deficiency renders the muscle energy deficient, impairs performance in treadmill exercise and prevents regeneration after exercise-induced tissue damage.

Effect of heart failure on catecholamine granule morphology and storage in chromaffin cells

One of the key mechanisms involved in sympathoexcitation in chronic heart failure (HF) is the activation of the adrenal glands. Impact of the elevated catecholamines on the hemodynamic parameters has been previously demonstrated. However, studies linking the structural effects of such overactivation with secretory performance and cell metabolism in the adrenomedullary chromaffin cells in vivo have not been previously reported. In this study, HF was induced in male Sprague-Dawley rats by ligation of the left coronary artery. Five weeks after surgery, cardiac function was assessed by ventricular hemodynamics. HF rats showed increased adrenal weight and adrenal catecholamine levels (norepinephrine, epinephrine and dopamine) compared with sham-operated rats. Rats with HF demonstrated increased small synaptic and dense core vesicle in splanchnic-adrenal synapses indicating trans-synaptic activation of catecholamine biosynthetic enzymes, increased endoplasmic reticulum and Golgi lumen width to meet the demand of increased catecholamine synthesis and release, and more mitochondria with dilated cristae and glycogen to accommodate for the increased energy demand for the increased biogenesis and exocytosis of catecholamines from the adrenal medulla. These findings suggest that increased trans-synaptic activation of the chromaffin cells within the adrenal medulla may lead to increased catecholamines in the circulation which in turn contributes to the enhanced neurohumoral drive, providing a unique mechanistic insight for enhanced catecholamine levels in plasma commonly observed in chronic HF condition.

Tissue plasminogen activator (t-PA) is targeted to the regulated secretory pathway. Catecholamine storage vesicles as a reservoir for the rapid release of t-PA

Tissue-type plasminogen activator (t-PA) is a serine protease that plays a central role in the regulation of intravascular thrombolysis. The acute release of t-PA in vivo is induced by a variety of stimuli including exercise, trauma, and neural stimulation. These types of stimuli also result in sympathoadrenal activation and exocytotic release of amines and proteins from catecholamine storage vesicles of the adrenal medulla and sympathetic neurons. Therefore, we tested the hypothesis that t-PA is packaged in and released directly from catecholamine storage vesicles, using several chromaffin cell sources including the rat pheochromocytoma PC-12 chromaffin cell line, primary cultures of bovine adrenal chromaffin cells, and human pheochromocytoma. t-PA was expressed in chromaffin cells as detected by Northern blotting, immunoprecipitation of [35S]Met-labeled t-PA, and specific t-PA enzyme-linked immunosorbent assay of cell homogenates. In addition, chromaffin cell t-PA was enzymatically active by fibrin zymography. To explore the subcellular localization of the expressed t-PA, PC-12 cells were labeled with [3H]norepinephrine, homogenized, and subjected to sucrose density fractionation. [3H]Norepinephrine and t-PA antigen were co-localized to the same subcellular fraction with a major peak at 1.4 M sucrose, consistent with the buoyant density of catecholamine storage vesicles. In addition, catecholamine storage vesicle lysates isolated from human pheochromocytoma tumors were enriched approximately 30-fold in t-PA antigen, compared with tumor homogenate. Furthermore, exposure of PC-12 cells or primary bovine adrenal chromaffin cells to chromaffin cell secretagogues (60 microM nicotine, 55 mM KCl, or 2 mM BaCl2) resulted in co-release of t-PA in parallel with catecholamines. These data demonstrate that t-PA is expressed in chromaffin cells, is sorted into the regulated pathway of secretion, and is co-released with catecholamines by chromaffin cell stimulation. Catecholamine storage vesicles may be an important reservoir and sympathoadrenal activation an important physiologic mechanism for the rapid release of t-PA. In addition, expression of t-PA by chromaffin cells suggests a role for this protease in the proteolytic processing of chromaffin cell proteins.