Nicotinamide riboside kinase 1 protects against diet and age-induced pancreatic ß-cell failure.

OBJECTIVE: Disturbances in NAD+ metabolism have been described as a hallmark for multiple metabolic and age-related diseases, including type 2 diabetes. While alterations in pancreatic ß-cell function are critical determinants of whole-body glucose homeostasis, the role of NAD+ metabolism in the endocrine pancreas remains poorly explored. Here, we aimed to evaluate the role of nicotinamide riboside (NR) metabolism in maintaining NAD+ levels and pancreatic ß-cell function in pathophysiological conditions. METHODS: Whole body and pancreatic ß-cell-specific NRK1 knockout (KO) mice were metabolically phenotyped in situations of high-fat feeding and aging. We also analyzed pancreatic ß-cell function, ß-cell mass and gene expression. RESULTS: We first demonstrate that NRK1, the essential enzyme for the utilization of NR, is abundantly expressed in pancreatic ß-cells. While NR treatment did not alter glucose-stimulated insulin secretion in pancreatic islets from young healthy mice, NRK1 knockout mice displayed glucose intolerance and compromised ß-cells response to a glucose challenge upon high-fat feeding or aging. Interestingly, ß cell dysfunction stemmed from the functional failure of other organs, such as liver and kidney, and the associated changes in circulating peptides and hormones, as mice lacking NRK1 exclusively in ß-cells did not show altered glucose homeostasis. CONCLUSIONS: This work unveils a new physiological role for NR metabolism in the maintenance of glucose tolerance and pancreatic ß-cell function in high-fat feeding or aging conditions.

Crosstalk between Drp1 phosphorylation sites during mitochondrial remodeling and their impact on metabolic adaptation.

Mitochondria constantly undergo fusion and fission events, referred as mitochondrial dynamics, which determine mitochondrial architecture and bioenergetics. Cultured cell studies demonstrate that mitochondrial dynamics are acutely regulated by phosphorylation of the mitochondrial fission orchestrator dynamin-related protein 1 (Drp1) at S579 or S600. However, the physiological impact and crosstalk of these phosphorylation sites is poorly understood. Here, we describe the functional interrelation between S579 and S600 phosphorylation sites in vivo and their role on mitochondrial remodeling. Mice carrying a homozygous Drp1 S600A knockin (Drp1 KI) mutation display larger mitochondria and enhanced lipid oxidation and respiratory capacities, granting improved glucose tolerance and thermogenic response upon high-fat feeding. Housing mice at thermoneutrality blunts these differences, suggesting a role for the brown adipose tissue in the protection of Drp1 KI mice against metabolic damage. Overall, we demonstrate crosstalk between Drp1 phosphorylation sites and provide evidence that their modulation could be used in the treatment and prevention of metabolic diseases.

Endogenous nicotinamide riboside metabolism protects against diet-induced liver damage.

Supplementation with the NAD+ precursor nicotinamide riboside (NR) ameliorates and prevents a broad array of metabolic and aging disorders in mice. However, little is known about the physiological role of endogenous NR metabolism. We have previously shown that NR kinase 1 (NRK1) is rate-limiting and essential for NR-induced NAD+ synthesis in hepatic cells. To understand the relevance of hepatic NR metabolism, we generated whole body and liver-specific NRK1 knockout mice. Here, we show that NRK1 deficiency leads to decreased gluconeogenic potential and impaired mitochondrial function. Upon high-fat feeding, NRK1 deficient mice develop glucose intolerance, insulin resistance and hepatosteatosis. Furthermore, they are more susceptible to diet-induced liver DNA damage, due to compromised PARP1 activity. Our results demonstrate that endogenous NR metabolism is critical to sustain hepatic NAD+ levels and hinder diet-induced metabolic damage, highlighting the relevance of NRK1 as a therapeutic target for metabolic disorders.

Circadian Rhythms and Mitochondria: Connecting the Dots.

Circadian rhythms provide a selective advantage by anticipating organismal nutrient needs and guaranteeing optimal metabolic capacity during active hours. Impairment of circadian rhythms is associated with increased risk of type 2 diabetes and emerging evidence suggests that metabolic diseases are linked to perturbed clock machinery. The circadian clock regulates many transcriptional-translational processes influencing whole cell metabolism and particularly mitochondrial activity. In this review, we survey the current literature related to cross-talks between mitochondria and the circadian clock and unravel putative molecular links. Understanding the mechanisms that link metabolism and circadian responses to transcriptional modifications will provide valuable insights toward innovative therapeutic strategies to combat the development of metabolic disease.

Mitochondrial stress management: a dynamic journey.

Mitochondria undergo continuous challenges in the course of their life, from their generation to their degradation. These challenges include the management of reactive oxygen species, the proper assembly of mitochondrial respiratory complexes and the need to balance potential mutations in the mitochondrial DNA. The detection of damage and the ability to keep it under control is critical to fine-tune mitochondrial function to the organismal energy needs. In this review, we will analyze the multiple mechanisms that safeguard mitochondrial function in light of in crescendo damage. This sequence of events will include initial defense against excessive reactive oxygen species production, compensation mechanisms by the unfolded protein response (UPRmt), mitochondrial dynamics and elimination by mitophagy.

Mfn2 is critical for brown adipose tissue thermogenic function.

Mitochondrial fusion and fission events, collectively known as mitochondrial dynamics, act as quality control mechanisms to ensure mitochondrial function and fine-tune cellular bioenergetics. Defective mitofusin 2 (Mfn2) expression and enhanced mitochondrial fission in skeletal muscle are hallmarks of insulin-resistant states. Interestingly, Mfn2 is highly expressed in brown adipose tissue (BAT), yet its role remains unexplored. Using adipose-specific Mfn2 knockout (Mfn2-adKO) mice, we demonstrate that Mfn2, but not Mfn1, deficiency in BAT leads to a profound BAT dysfunction, associated with impaired respiratory capacity and a blunted response to adrenergic stimuli. Importantly, Mfn2 directly interacts with perilipin 1, facilitating the interaction between the mitochondria and the lipid droplet in response to adrenergic stimulation. Surprisingly, Mfn2-adKO mice were protected from high-fat diet-induced insulin resistance and hepatic steatosis. Altogether, these results demonstrate that Mfn2 is a mediator of mitochondria to lipid droplet interactions, influencing lipolytic processes and whole-body energy homeostasis.

Estudio de factores histológicos predictivos de metástasis ganglionar locorregional en adenocarcinoma colorrectal mínimamente invasivo pT1 / Histological factors predicting loco-regional lymph node metastasis in early invasive colorectal adenocarcinoma pT1

INTRODUCCIÓN: El tratamiento habitual del adenocarcinoma colorrectal pT1 consiste en la resección endoscópica siempre que sea posible. Se requiere la evaluación de los ganglios linfáticos locorregionales cuando se detectan factores histológicos adversos en las polipectomías endoscópicas. MATERIALES Y MÉTODOS: Se seleccionaron 29 adenocarcinomas colorrectales pT1 incluyendo las polipectomías endoscópicas y piezas quirúrgicas correspondientes. Se evaluaron por 2 patólogos todos los parámetros histológicos asociados a N+, incluyendo: grado de diferenciación tumoral, profundidad de invasión en submucosa, invasión angiolinfática (IAL), invasión perineural, inflamación crónica, gemaciones tumorales, grupos de tumor pobremente diferenciados, adenoma preexistente, borde tumoral y margen de resección endoscópico. Se realizó un análisis de regresión logística univariante y multivariante para evaluar la capacidad individual de cada variable para predecir N+. RESULTADOS: En el análisis univariante, la localización rectal, la presencia de IAL y la presencia de grupos de tumor pobremente diferenciados se asociaron significativamente con metástasis ganglionares. De todas estas variables, la presencia de IAL presentó la mayor área bajo la curva ROC (0,875). El análisis multivariante no encontró ninguna variable independiente asociada a N+. CONCLUSIONES: La IAL y la presencia de grupos de tumor pobremente diferenciados se asocia frecuentemente con N+ en cáncer colorrectal precoz, por lo que se debe implementar rutinariamente la evaluación de estos parámetros histológicos

INTRODUCTION: Endoscopic resection is the common treatment in pT1 colorectal adenocarcinoma whenever possible. The presence of adverse histological factors requires subsequent lymph node evaluation. MATERIALS AND METHODS: We selected 29 colorectal pT1 adenocarcinoma including endoscopic polypectomies and the corresponding surgical specimens. All histologic parameters associated with N+ were evaluated by 2 pathologists, including: tumor differentiation grade, depth of invasion in the submucosa, angiolymphatic invasion (ALI), perineural invasion, chronic inflammation, tumor budding, poorly differentiated cluster, pre-existing adenoma, tumor border, and endoscopic resection margin. Univariate and multivariate logistic regression analysis were performed to assess the individual capacity of each variable to predict N+. Results In the univariate analysis, rectal tumor localization, ALI and poorly differentiated cluster was significantly associated with N+. Among the significant parameters, ALI had the highest area under the ROC curve (0.875). Multivariate analysis showed no independent variables associated with N+. CONCLUSIONS: We confirm that ALI and the presence of poorly differentiated cluster are frequently associated with N+ in early colorectal cancer. Consequently, these parameters should be routinely evaluated by pathologists

[Histological factors predicting loco-regional lymph node metastasis in early invasive colorectal adenocarcinoma pT1]. / Estudio de factores histológicos predictivos de metástasis ganglionar locorregional en adenocarcinoma colorrectal mínimamente invasivo pT1.

INTRODUCTION: Endoscopic resection is the common treatment in pT1 colorectal adenocarcinoma whenever possible. The presence of adverse histological factors requires subsequent lymph node evaluation. MATERIALS AND METHODS: We selected 29 colorectal pT1 adenocarcinoma including endoscopic polypectomies and the corresponding surgical specimens. All histologic parameters associated with N+ were evaluated by 2 pathologists, including: tumor differentiation grade, depth of invasion in the submucosa, angiolymphatic invasion (ALI), perineural invasion, chronic inflammation, tumor budding, poorly differentiated cluster, pre-existing adenoma, tumor border, and endoscopic resection margin. Univariate and multivariate logistic regression analysis were performed to assess the individual capacity of each variable to predict N+. RESULTS: In the univariate analysis, rectal tumor localization, ALI and poorly differentiated cluster was significantly associated with N+. Among the significant parameters, ALI had the highest area under the ROC curve (0.875). Multivariate analysis showed no independent variables associated with N+. CONCLUSIONS: We confirm that ALI and the presence of poorly differentiated cluster are frequently associated with N+ in early colorectal cancer. Consequently, these parameters should be routinely evaluated by pathologists.