Chemical and Genetic Modulation of Complex I of the Electron Transport Chain Enhances the Biotherapeutic Protein Production Capacity of CHO Cells.

Chinese hamster ovary (CHO) cells are the cell line of choice for producing recombinant therapeutic proteins. Despite improvements in production processes, reducing manufacturing costs remains a key driver in the search for more productive clones. To identify media additives capable of increasing protein production, CHOZN® GS-/- cell lines were screened with 1280 small molecules, and two were identified, forskolin and BrdU, which increased productivity by ≥40%. While it is possible to incorporate these small molecules into a commercial-scale process, doing so may not be financially feasible or could raise regulatory concerns related to the purity of the final drug substance. To circumvent these issues, RNA-Seq was performed to identify transcripts which were up- or downregulated upon BrdU treatment. Subsequent Reactome pathway analysis identified the electron transport chain as an affected pathway. CRISPR/Cas9 was utilized to create missense mutations in two independent components of the electron transport chain and the resultant clones partially recapitulated the phenotypes observed upon BrdU treatment, including the productivity of recombinant therapeutic proteins. Together, this work suggests that BrdU can enhance the productivity of CHO cells by modulating cellular energetics and provides a blueprint for translating data from small molecule chemical screens into genetic engineering targets to improve the performance of CHO cells. This could ultimately lead to more productive host cell lines and a more cost-effective method of supplying medication to patients.

A soluble endoplasmic reticulum factor as regenerative therapy for Wolfram syndrome.

Endoplasmic reticulum (ER) stress-mediated cell death is an emerging target for human chronic disorders, including neurodegeneration and diabetes. However, there is currently no treatment for preventing ER stress-mediated cell death. Here, we show that mesencephalic astrocyte-derived neurotrophic factor (MANF), a neurotrophic factor secreted from ER stressed cells, prevents ER stress-mediated ß cell death and enhances ß cell proliferation in cell and mouse models of Wolfram syndrome, a prototype of ER disorders. Our results indicate that molecular pathways regulated by MANF are promising therapeutic targets for regenerative therapy of ER stress-related disorders, including diabetes, retinal degeneration, neurodegeneration, and Wolfram syndrome.

Pancreatic stone protein/regenerating protein is a potential biomarker for endoplasmic reticulum stress in beta cells.

Endoplasmic reticulum (ER) stress in beta cells is an important pathogenic component of both type 1 and type 2 diabetes mellitus, as well as genetic forms of diabetes, especially Wolfram syndrome. However, there are currently no convenient ways to assess ER stress in beta cells, raising the need for circulating ER stress markers indicative of beta cell health. Here we show that pancreatic stone protein/regenerating protein (PSP/reg) is a potential biomarker for ER stressed beta cells. PSP/reg levels are elevated in cell culture and mouse models of Wolfram syndrome, a prototype of ER stress-induced diabetes. Moreover, PSP/reg expression is induced by the canonical chemical inducers of ER stress, tunicamycin and thapsigargin. Circulating PSP/reg levels are also increased in some patients with Wolfram syndrome. Our results therefore reveal PSP/reg as a potential biomarker for beta cells under chronic ER stress, as is the case in Wolfram syndrome.

Nrf2/antioxidant pathway mediates ß cell self-repair after damage by high-fat diet-induced oxidative stress.

Many theories have been advanced to better understand why ß cell function and structure relentlessly deteriorate during the course of type 2 diabetes (T2D). These theories include inflammation, apoptosis, replication, neogenesis, autophagy, differentiation, dedifferentiation, and decreased levels of insulin gene regulatory proteins. However, none of these have considered the possibility that endogenous self-repair of existing ß cells may be an important factor. To examine this hypothesis, we conducted studies with female Zucker diabetic fatty rats fed a high-fat diet (HFD) for 1, 2, 4, 7, 9, 18, or 28 days, followed by a return to regular chow for 2-3 weeks. Repair was defined as reversal of elevated blood glucose and of inappropriately low blood insulin levels caused by a HFD, as well as reversal of structural damage visualized by imaging studies. We observed evidence of functional ß cell damage after a 9-day exposure to a HFD and then repair after 2-3 weeks of being returned to normal chow (blood glucose [BG] = 348 ± 30 vs. 126 ± 3; mg/dl; days 9 vs. 23 day, P < 0.01). After 18- and 28-day exposure to a HFD, damage was more severe and repair was less evident. Insulin levels progressively diminished with 9-day exposure to a HFD; after returning to a regular diet, insulin levels rebounded toward, but did not reach, normal values. Increase in ß cell mass was 4-fold after 9 days and 3-fold after 18 days, and there was no increase after 28 days of a HFD. Increases in ß cell mass during a HFD were not different when comparing values before and after a return to regular diet within the 9-, 18-, or 28-day studies. No changes were observed in apoptosis or ß cell replication. Formation of intracellular markers of oxidative stress, intranuclear translocation of Nrf2, and formation of intracellular antioxidant proteins indicated the participation of HFD/oxidative stress induction of the Nrf2/antioxidant pathway. Flow cytometry-based assessment of ß cell volume, morphology, and insulin-specific immunoreactivity, as well as ultrastructural analysis by transmission electron microscopy, revealed that short-term exposure to a HFD produced significant changes in ß cell morphology and function that are reversible after returning to regular chow. These results suggest that a possible mechanism mediating the ability of ß cells to self-repair after a short-term exposure to a HFD is the activation of the Nrf2/antioxidant pathway.

Intermittent fasting preserves beta-cell mass in obesity-induced diabetes via the autophagy-lysosome pathway.

Obesity-induced diabetes is characterized by hyperglycemia, insulin resistance, and progressive beta cell failure. In islets of mice with obesity-induced diabetes, we observe increased beta cell death and impaired autophagic flux. We hypothesized that intermittent fasting, a clinically sustainable therapeutic strategy, stimulates autophagic flux to ameliorate obesity-induced diabetes. Our data show that despite continued high-fat intake, intermittent fasting restores autophagic flux in islets and improves glucose tolerance by enhancing glucose-stimulated insulin secretion, beta cell survival, and nuclear expression of NEUROG3, a marker of pancreatic regeneration. In contrast, intermittent fasting does not rescue beta-cell death or induce NEUROG3 expression in obese mice with lysosomal dysfunction secondary to deficiency of the lysosomal membrane protein, LAMP2 or haplo-insufficiency of BECN1/Beclin 1, a protein critical for autophagosome formation. Moreover, intermittent fasting is sufficient to provoke beta cell death in nonobese lamp2 null mice, attesting to a critical role for lysosome function in beta cell homeostasis under fasting conditions. Beta cells in intermittently-fasted LAMP2- or BECN1-deficient mice exhibit markers of autophagic failure with accumulation of damaged mitochondria and upregulation of oxidative stress. Thus, intermittent fasting preserves organelle quality via the autophagy-lysosome pathway to enhance beta cell survival and stimulates markers of regeneration in obesity-induced diabetes.

Targeting Cellular Calcium Homeostasis to Prevent Cytokine-Mediated Beta Cell Death.

Pro-inflammatory cytokines are important mediators of islet inflammation, leading to beta cell death in type 1 diabetes. Although alterations in both endoplasmic reticulum (ER) and cytosolic free calcium levels are known to play a role in cytokine-mediated beta cell death, there are currently no treatments targeting cellular calcium homeostasis to combat type 1 diabetes. Here we show that modulation of cellular calcium homeostasis can mitigate cytokine- and ER stress-mediated beta cell death. The calcium modulating compounds, dantrolene and sitagliptin, both prevent cytokine and ER stress-induced activation of the pro-apoptotic calcium-dependent enzyme, calpain, and partly suppress beta cell death in INS1E cells and human primary islets. These agents are also able to restore cytokine-mediated suppression of functional ER calcium release. In addition, sitagliptin preserves function of the ER calcium pump, sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), and decreases levels of the pro-apoptotic protein thioredoxin-interacting protein (TXNIP). Supporting the role of TXNIP in cytokine-mediated cell death, knock down of TXNIP in INS1-E cells prevents cytokine-mediated beta cell death. Our findings demonstrate that modulation of dynamic cellular calcium homeostasis and TXNIP suppression present viable pharmacologic targets to prevent cytokine-mediated beta cell loss in diabetes.

Dominant ER Stress-Inducing WFS1 Mutations Underlie a Genetic Syndrome of Neonatal/Infancy-Onset Diabetes, Congenital Sensorineural Deafness, and Congenital Cataracts.

Neonatal diabetes is frequently part of a complex syndrome with extrapancreatic features: 18 genes causing syndromic neonatal diabetes have been identified to date. There are still patients with neonatal diabetes who have novel genetic syndromes. We performed exome sequencing in a patient and his unrelated, unaffected parents to identify the genetic etiology of a syndrome characterized by neonatal diabetes, sensorineural deafness, and congenital cataracts. Further testing was performed in 311 patients with diabetes diagnosed before 1 year of age in whom all known genetic causes had been excluded. We identified 5 patients, including the initial case, with three heterozygous missense mutations in WFS1 (4/5 confirmed de novo). They had diabetes diagnosed before 12 months (2 before 6 months) (5/5), sensorineural deafness diagnosed soon after birth (5/5), congenital cataracts (4/5), and hypotonia (4/5). In vitro studies showed that these WFS1 mutations are functionally different from the known recessive Wolfram syndrome-causing mutations, as they tend to aggregate and induce robust endoplasmic reticulum stress. Our results establish specific dominant WFS1 mutations as a cause of a novel syndrome including neonatal/infancy-onset diabetes, congenital cataracts, and sensorineural deafness. This syndrome has a discrete pathophysiology and differs genetically and clinically from recessive Wolfram syndrome.

Silymarin Activates c-AMP Phosphodiesterase and Stimulates Insulin Secretion in a Glucose-Dependent Manner in HIT-T15 Cells.

Silymarin (SIL) is a flavonoid extracted from milk thistle seed that has been reported to decrease hyperglycemia in people with type 2 diabetes (T2D). However, it is not known whether SIL has direct secretory effects on ß-cells. Using the ß-cell line HIT-T15, SIL was shown to decrease intracellular peroxide levels and to augment glucose-stimulated insulin secretion (GSIS). However, the latter was observed using a concentration range of 25-100 µM, which was too low to affect endogenous peroxide levels. The stimulatory effect of SIL dissipated at higher concentrations (100-200 µM), and mild apoptosis was observed. The smaller concentrations of SIL also decreased cAMP phosphodiesterase activity in a Ca2+/calmodulin-dependent manner. The stimulatory effects of SIL on GSIS were inhibited by three different inhibitors of exocytosis, indicating that SIL's mechanism of stimulating GSIS operated via closing ß-cell K-ATP channels, and perhaps more distal sites of action involving calcium influx and G-proteins. We concluded that augmentation of GSIS by SIL can be observed at concentrations that also inhibit cAMP phosphodiesterase without concomitant lowering of intracellular peroxides.

Rpl13a small nucleolar RNAs regulate systemic glucose metabolism.

Small nucleolar RNAs (snoRNAs) are non-coding RNAs that form ribonucleoproteins to guide covalent modifications of ribosomal and small nuclear RNAs in the nucleus. Recent studies have also uncovered additional non-canonical roles for snoRNAs. However, the physiological contributions of these small RNAs are largely unknown. Here, we selectively deleted four snoRNAs encoded within the introns of the ribosomal protein L13a (Rpl13a) locus in a mouse model. Loss of Rpl13a snoRNAs altered mitochondrial metabolism and lowered reactive oxygen species tone, leading to increased glucose-stimulated insulin secretion from pancreatic islets and enhanced systemic glucose tolerance. Islets from mice lacking Rpl13a snoRNAs demonstrated blunted oxidative stress responses. Furthermore, these mice were protected against diabetogenic stimuli that cause oxidative stress damage to islets. Our study illuminates a previously unrecognized role for snoRNAs in metabolic regulation.

Poly-dipeptides encoded by the C9ORF72 repeats block global protein translation.

The expansion of the GGGGCC hexanucleotide repeat in the non-coding region of the Chromosome 9 open-reading frame 72 (C9orf72) gene is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). This genetic alteration leads to the accumulation of five types of poly-dipeptides translated from the GGGGCC hexanucleotide repeat. Among these, poly-proline-arginine (poly-PR) and poly-glycine-arginine (poly-GR) peptides are known to be neurotoxic. However, the mechanisms of neurotoxicity associated with these poly-dipeptides are not clear. A proteomics approach identified a number of interacting proteins with poly-PR peptide, including mRNA-binding proteins, ribosomal proteins, translation initiation factors and translation elongation factors. Immunostaining of brain sections from patients with C9orf72 ALS showed that poly-GR was colocalized with a mRNA-binding protein, hnRNPA1. In vitro translation assays showed that poly-PR and poly-GR peptides made insoluble complexes with mRNA, restrained the access of translation factors to mRNA, and blocked protein translation. Our results demonstrate that impaired protein translation mediated by poly-PR and poly-GR peptides plays a role in neurotoxicity and reveal that the pathways altered by the poly-dipeptides-mRNA complexes are potential therapeutic targets for treatment of C9orf72 FTD/ALS.

A calcium-dependent protease as a potential therapeutic target for Wolfram syndrome.

Wolfram syndrome is a genetic disorder characterized by diabetes and neurodegeneration and considered as an endoplasmic reticulum (ER) disease. Despite the underlying importance of ER dysfunction in Wolfram syndrome and the identification of two causative genes, Wolfram syndrome 1 (WFS1) and Wolfram syndrome 2 (WFS2), a molecular mechanism linking the ER to death of neurons and ß cells has not been elucidated. Here we implicate calpain 2 in the mechanism of cell death in Wolfram syndrome. Calpain 2 is negatively regulated by WFS2, and elevated activation of calpain 2 by WFS2-knockdown correlates with cell death. Calpain activation is also induced by high cytosolic calcium mediated by the loss of function of WFS1. Calpain hyperactivation is observed in the WFS1 knockout mouse as well as in neural progenitor cells derived from induced pluripotent stem (iPS) cells of Wolfram syndrome patients. A small-scale small-molecule screen targeting ER calcium homeostasis reveals that dantrolene can prevent cell death in neural progenitor cells derived from Wolfram syndrome iPS cells. Our results demonstrate that calpain and the pathway leading its activation provides potential therapeutic targets for Wolfram syndrome and other ER diseases.

Calcium efflux from the endoplasmic reticulum leads to ß-cell death.

It has been established that intracellular calcium homeostasis is critical for survival and function of pancreatic ß-cells. However, the role of endoplasmic reticulum (ER) calcium homeostasis in ß-cell survival and death is not clear. Here we show that ER calcium depletion plays a critical role in ß-cell death. Various pathological conditions associated with ß-cell death, including ER stress, oxidative stress, palmitate, and chronic high glucose, decreased ER calcium levels and sarcoendoplasmic reticulum Ca(2+)-ATPase 2b expression, leading to ß-cell death. Ectopic expression of mutant insulin and genetic ablation of WFS1, a causative gene for Wolfram syndrome, also decreased ER calcium levels and induced ß-cell death. Hyperactivation of calpain-2, a calcium-dependent proapoptotic protease, was detected in ß-cells undergoing ER calcium depletion. Ectopic expression of sarcoendoplasmic reticulum Ca(2+)-ATPase 2b, as well as pioglitazone and rapamycin treatment, could prevent calcium efflux from the ER and mitigate ß-cell death under various stress conditions. Our results reveal a critical role of ER calcium depletion in ß-cell death and indicate that identification of pathways and chemical compounds restoring ER calcium levels will lead to novel therapeutic modalities and pharmacological interventions for type 1 and type 2 diabetes and other ER-related diseases including Wolfram syndrome.

Autosomal dominant diabetes arising from a Wolfram syndrome 1 mutation.

We used an unbiased genome-wide approach to identify exonic variants segregating with diabetes in a multigenerational Finnish family. At least eight members of this family presented with diabetes with age of diagnosis ranging from 18 to 51 years and a pattern suggesting autosomal dominant inheritance. We sequenced the exomes of four affected members of this family and performed follow-up genotyping of additional affected and unaffected family members. We uncovered a novel nonsynonymous variant (p.Trp314Arg) in the Wolfram syndrome 1 (WFS1) gene that segregates completely with the diabetic phenotype. Multipoint parametric linkage analysis with 13 members of this family identified a single linkage signal with maximum logarithm of odds score 3.01 at 4p16.2-p16.1, corresponding to a region harboring the WFS1 locus. Functional studies demonstrate a role for this variant in endoplasmic reticulum stress, which is consistent with the ß-cell failure phenotype seen in mutation carriers. This represents the first compelling report of a mutation in WFS1 associated with dominantly inherited nonsyndromic adult-onset diabetes.

Ebselen treatment prevents islet apoptosis, maintains intranuclear Pdx-1 and MafA levels, and preserves ß-cell mass and function in ZDF rats.

We reported earlier that ß-cell-specific overexpression of glutathione peroxidase (GPx)-1 significantly ameliorated hyperglycemia in diabetic db/db mice and prevented glucotoxicity-induced deterioration of ß-cell mass and function. We have now ascertained whether early treatment of Zucker diabetic fatty (ZDF) rats with ebselen, an oral GPx mimetic, will prevent ß-cell deterioration. No other antihyperglycemic treatment was given. Ebselen ameliorated fasting hyperglycemia, sustained nonfasting insulin levels, lowered nonfasting glucose levels, and lowered HbA1c levels with no effects on body weight. Ebselen doubled ß-cell mass, prevented apoptosis, prevented expression of oxidative stress markers, and enhanced intranuclear localization of pancreatic and duodenal homeobox (Pdx)-1 and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (MafA), two critical insulin transcription factors. Minimal ß-cell replication was observed in both groups. These findings indicate that prevention of oxidative stress is the mechanism whereby ebselen prevents apoptosis and preserves intranuclear Pdx-1 and MafA, which, in turn, is a likely explanation for the beneficial effects of ebselen on ß-cell mass and function. Since ebselen is an oral antioxidant currently used in clinical trials, it is a novel therapeutic candidate to ameliorate fasting hyperglycemia and further deterioration of ß-cell mass and function in humans undergoing the onset of type 2 diabetes.