Rodent models of metabolic disorders: considerations for use in studies of neonatal programming

Epidemiologically, metabolic disorders have garnered much attention, perhaps due to the predominance of obesity. The early postnatal life represents a critical period for programming multifactorial metabolic disorders of adult life. Though, altricial rodents are prime subjects for investigating neonatal programming, there is still no sufficiently generalised literature on their usage and methodology. This review focuses on establishing five approach-based models of neonatal rodents adopted for studying metabolic phenotypes. Here, some modelled interventions that currently exist to avoid or prevent metabolic disorders are also highlighted. We also bring forth recommendations, guidelines, and considerations to aid research on neonatal programming. It is hoped that this provides a background to researchers focused on the aetiology, mechanisms, prevention and treatment of metabolic disorders.

Impacts of Nutritional Management During Early Postnatal Life on Long-Term Physiological and Productive Responses of Beef Cattle

Effective early postnatal nutritional management is a crucial component of livestock production systems, and nutrient manipulation during this period has been shown to exert long-term consequences on beef cattle growth and physiology. Metabolic imprinting defines these biological responses to a nutritional intervention early in life that permanently alter physiological outcomes later in life. Early weaning has been used to study metabolic imprinting effects, given that it allows for nutritional manipulation of animals at a young age. This practice has been shown to enhance carcass characteristics in feedlot cattle and accelerate reproductive development of females. Another strategy to study the effects of metabolic imprinting without the need for early weaning is to provide supplements via creep feeding. Providing creep feed to nursing cattle has resulted in transient and long-term alterations in cattle metabolism, contributing to increased reproductive performance of developing heifers and enhanced carcass quality of feeder cattle. Collectively, results described herein demonstrate nutrient manipulation during early postnatal life exerts long-term consequences on beef cattle productivity and may be a strategy to optimize production efficiency in beef cattle systems.

Phenotypic diversity and sensitivity to injury of the pulmonary endothelium during a period of rapid postnatal growth

BackgroundEndothelial cells (EC) sit at the forefront of dramatic physiologic changes occurring in the pulmonary circulation during late embryonic and early postnatal life. First, as the lung moves from the hypoxic fetal environment to oxygen-rich postnatal environment, marked changes in pulmonary EC structure and function facilitate a marked increase in blood flow from the placenta to the lungs. Subsequently, pulmonary angiogenesis expands the microvasculature to drive exponential distal lung growth during early postnatal life. Yet, how these marked physiologic changes alter distinct EC subtypes to facilitate the transition of the pulmonary circulation and regulate vascular growth and remodeling remains incompletely understood.MethodsIn this report, we employed single cell RNA-transcriptomics and in situ RNA imaging to profile pulmonary EC in the developing mouse lung from just before birth through this period of rapid postnatal growth.ResultsMultiple, transcriptionally distinct macro- and microvascular EC were identified in the late embryonic and early postnatal lung, with gene expression profiles distinct from their adult EC counterparts. A novel arterial subtype, unique to the developing lung localized to the distal parenchyma and expressed genes that regulate vascular growth and patterning. Birth particularly heightened microvascular diversity, inducing dramatic shifts in the transcriptome of distinct microvascular subtypes in pathways related to proliferation, migration and antigen presentation. Two distinct waves of EC proliferation were identified, including one just prior to birth, and a second during early alveolarization, a time of exponential pulmonary angiogenesis. Chronic hyperoxia, an injury that impairs parenchymal and vascular growth, induced a common gene signature among all pulmonary EC, unique alterations to distinct microvascular EC subtypes, and disrupted EC-EC and EC-immune cell cross talk.ConclusionsTaken together, these data reveal tremendous diversity of pulmonary EC during a critical window of postnatal vascular growth, and provide a detailed molecular map that can be used to inform both normal vascular development and alterations in EC diversity upon injury. These data have important implications for lung diseases marked by dysregulated angiogenesis and pathologic pulmonary vascular remodeling.

Prematurity and postnatal alterations in intermittent hypoxaemia

Intermittent hypoxaemia (IH) events are well described in extremely preterm infants, but the occurrence of IH patterns in more mature preterm infants remains unclear. The objective of this study was to characterise the effect of gestational age on early postnatal patterns of IH in extremely (<28 weeks), very (28–<32 weeks) and moderately (32–<34 weeks) preterm infants. As expected, extremely preterm infants had a significantly higher frequency of IH events of longer durations and greater time with hypoxaemia versus very and moderately preterm infants. In addition, the postnatal decrease in IH duration was comparable in the very and moderately preterm infants. This progression of IH events should assist clinicians and families in managing expectations for resolution of IH events during early postnatal life.

Natriuretic peptides and Forkhead O transcription factors act in a cooperative manner to promote cardiomyocyte cell cycle re-entry in the postnatal mouse heart

Background Cardiomyocytes proliferate rapidly during fetal life but lose their ability of proliferation soon after birth. However, before terminal withdrawal from the cell cycle, cardiomyocytes undergo another round of cell cycle during early postnatal life in mice. While a transient wave of increased DNA synthesis in cardiomyocyte has been observed in postnatal mouse hearts, the molecular mechanisms describing cardiomyocyte cell cycle re-entry remain poorly understood. Atrial and B-type natriuretic peptides (ANP and BNP) are abundantly expressed in embryonic heart ventricles. After birth, the expression of both genes is strongly reduced in the ventricular myocardium. Forkhead O (FOXO) transcription factors are expressed in both embryonic and postnatal heart ventricles. Their transcriptional activity negatively affects cardiomyocyte proliferation. Upon phosphorylation, FOXO is translocated to the cytoplasm and is transcriptionally inactive. Despite these important findings, it remains largely unknown whether natriuretic peptides and FOXO cooperatively play a role in regulating cardiomyocyte cell cycle activity during early postnatal life. Results We observed that the expression of ANP and BNP and the level of phosphorylated FOXO were transiently increased in the postnatal mouse heart ventricles, which coincided with the burst of cardiomyocyte cell cycle re-entry during early postnatal life in mice. Cell culture studies showed that ANP/BNP signaling and FOXO cooperatively promoted cell cycle activity in neonatal mouse cardiomyocytes. The enhanced cell cycle activity observed in combined treatment of ANP/BNP and dominant-negative FOXO (DN-FOXO), which can bind FOXO recognition sites on DNA but cannot activate transcription, was primarily mediated through natriuretic peptide receptor 3 (Npr3). In mice, simultaneous application of ANP and DN-FOXO in postnatal hearts reactivated cell cycle in cardiomyocytes, resulting in reduced scar formation after experimental myocardial infarction. Conclusions Our data demonstrate the cooperative effects of natriuretic peptide and DN-FOXO on promoting cardiomyocyte cell cycle activity and mouse cardiac repair and regeneration after injury.

Changes in subclass-specific IgG Fc glycosylation associated with the postnatal maturation of the murine immune system

Early postnatal life is characterized by a critical time period in which the developing neonatal immune system transitions from passive immunity, induced by protective maternal antibodies, to the competence of a fully functioning immune system. The inflammatory capability of both maternal and neonatal antibodies is governed by N-linked glycosylation of the Fc region, and though this has been examined extensively in adults, there is currently little information regarding antibody glycosylation patterns during early postnatal life. To characterize the murine IgG Fc glycosylation profile during early life, we used nano-LC-ESI-Qq-TOF mass spectrometry analysis to assess subclass specific Asn-297 glycosylation patterns in the serum of BALB/c mice from 5–60 days of age. From birth to adulthood, we observed a decline in proinflammatory Fc glycosylation in all IgG subclasses. This was shown by significantly reduced agalactosylated and monogalactosylated structures combined with increased sialylation after weaning at 45 and 60 days of age. This information indicates that the transition between neonatal life and adulthood in mice is accompanied by reduction of inflammatory IgG antibodies. Our study contributes to a growing body of literature indicating the importance of IgG Fc glycosylation and its association with inflammation during different life stages.