Glucose Metabolism, Islet Architecture, and Genetic Homogeneity in Imprinting of [Ca2+]i and Insulin Rhythms in Mouse Islets

We reported previously that islets isolated from individual, outbred Swiss-Webster mice displayed oscillations in intracellular calcium ([Ca2+]i) that varied little between islets of a single mouse but considerably between mice, a phenomenon we termed “islet imprinting.” We have now confirmed and extended these findings in several respects. First, imprinting occurs in both inbred (C57BL/6J) as well as outbred mouse strains (Swiss-Webster; CD1). Second, imprinting was observed in NAD(P)H oscillations, indicating a metabolic component. Further, short-term exposure to a glucose-free solution, which transiently silenced [Ca2+]i oscillations, reset the oscillatory patterns to a higher frequency. This suggests a key role for glucose metabolism in maintaining imprinting, as transiently suppressing the oscillations with diazoxide, a KATP-channel opener that blocks [Ca2+]i influx downstream of glucose metabolism, did not change the imprinted patterns. Third, imprinting was not as readily observed at the level of single beta cells, as the [Ca2+]i oscillations of single cells isolated from imprinted islets exhibited highly variable, and typically slower [Ca2+]i oscillations. Lastly, to test whether the imprinted [Ca2+]i patterns were of functional significance, a novel microchip platform was used to monitor insulin release from multiple islets in real time. Insulin release patterns correlated closely with [Ca2+]i oscillations and showed significant mouse-to-mouse differences, indicating imprinting. These results indicate that islet imprinting is a general feature of islets and is likely to be of physiological significance. While islet imprinting did not depend on the genetic background of the mice, glucose metabolism and intact islet architecture may be important for the imprinting phenomenon

Functional Deficits in nNOSμ-Deficient Skeletal Muscle: Myopathy in nNOS Knockout Mice

Skeletal muscle nNOSμ (neuronal nitric oxide synthase mu) localizes to the sarcolemma through interaction with the dystrophin-associated glycoprotein (DAG) complex, where it synthesizes nitric oxide (NO). Disruption of the DAG complex occurs in dystrophinopathies and sarcoglycanopathies, two genetically distinct classes of muscular dystrophy characterized by progressive loss of muscle mass, muscle weakness and increased fatigability. DAG complex instability leads to mislocalization and downregulation of nNOSμ; but this is thought to play a minor role in disease pathogenesis. This view persists without knowledge of the role of nNOS in skeletal muscle contractile function in vivo and has influenced gene therapy approaches to dystrophinopathy, the majority of which do not restore sarcolemmal nNOSμ. We address this knowledge gap by evaluating skeletal muscle function in nNOS knockout (KN1) mice using an in situ approach, in which the muscle is maintained in its normal physiological environment. nNOS-deficiency caused reductions in skeletal muscle bulk and maximum tetanic force production in male mice only. Furthermore, nNOS-deficient muscles from both male and female mice exhibited increased susceptibility to contraction-induced fatigue. These data suggest that aberrant nNOSμ signaling can negatively impact three important clinical features of dystrophinopathies and sarcoglycanopathies: maintenance of muscle bulk, force generation and fatigability. Our study suggests that restoration of sarcolemmal nNOSμ expression in dystrophic muscles may be more important than previously appreciated and that it should be a feature of any fully effective gene therapy-based intervention

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Politically related stress and low-birth-weight infants among Arab, Asian, Hispanic, non-Hispanic Black, and non-Hispanic White women in Michigan

Background: Despite the high cost of low birth weight and the persistent challenge of racial inequities affecting the Arab American community, there has been limited research to identify and examine risk factors for these inequities with validated data on Arab American ethnicity and recent population stressors. Objectives: This study examined whether the 2016 presidential election is associated with low birth weight among non-Hispanic White, Arab American, Hispanic, and non-Hispanic Black women. Design: This population-based study of singleton births in Michigan (2008–2017) used an algorithm to identify mothers who were of Arab descent. Methods: We used logistic regression to estimate odds ratios and 95% confidence intervals for the association between race/ethnicity and the odds of low birth weight. We examined whether these associations differed before and after the 2016 presidential election and according to maternal education. Results: There were 1,019,738 births, including 66,272 (6.5%) classified as low birth weight. The odds of having a low-birth-weight infant were higher among all minority women compared to non-Hispanic White women. The association was similar before and after the 2016 presidential election and stronger among women with higher levels of education. Conclusion: This is the first study to estimate low birth weight among Arab American women in the context of political events. There are opportunities for future studies to discuss this issue in depth

Effects of weight gain with age on imprinting.

<p>(A–B) Representative examples of islet [Ca²⁺]_i patterns in 11 mM glucose among lean mice weighing <30 g (A) and aged/large mice weighing >40 g (B). (C) Mean period of oscillations among 10 lean and 3 aged/large Swiss-Webster mice. Mean weight and mean period of islet [Ca²⁺]_i oscillations differed between groups (p<0.001).</p

[Ca²⁺]_i flux and insulin release patterns show mouse-to-mouse imprinting.

<p>(A) [Ca²⁺]_i flux and insulin release traces from islets taken from three different mice (labeled accordingly). Displayed oscillation frequency averages are 9 min (Mouse 1), 4.5 min (Mouse 2), and 15 s (Mouse 6). Periods were calculated using local minimum values. Insulin oscillations from mouse 6 were faster than the measured temporal resolution (22 s) of the chip, causing under sampling of secretion dynamics. (B) Comparison of average [Ca²⁺]_i and insulin oscillation periods from each animal. Data sets are n≥6 islets and error bars are ±1 standard deviation. (C) Plot of average [Ca²⁺]_i versus insulin for each mouse. The linear relationship of data points suggests good agreement of oscillation frequencies (R² = 0.98; p<0.0001).</p

Dispersed beta cells do not display frank imprinting.

<p>(A) Representative examples of oscillatory patterns from 3 individual beta cells (A) and 3 islets (B) taken from the same mouse (Mouse 8 as indicated by the box in C). (C–D) Mean period ± SEM from 12 sets of beta cells (C) and corresponding islets (D) from the same mouse. Beta cells displayed longer period and also a greater degree of variability in their periods as noted by the large standard deviations they exhibited compared to islets. A total of 137 beta cells and 109 islets were recorded among 12 mice. One-way ANOVA indicates differences among beta-cell periods (P<0.01) and substantial differences among islet periods (p<1.0e-25) from mouse to mouse. (E) Scatter plot showing the relationship between oscillatory periods of beta cells and islets among the 12 mice studied (R² = 0.39, p = 0.22).</p

Both inbred and outbred mice display islet imprinting.

<p>(A–B) Two representative C57BL/6J mice out of a group of 9 displayed very different [Ca²⁺]_i oscillation patterns. Three representative islets from Mouse 6 display slow oscillations (A, period: 3.9±0.2 minutes, n = 12 islets total) and three representative islets from Mouse 5 display fast oscillations (B, period: 0.9±0.6 minutes, n = 9 islets total). One trace shown in B (bottom) shows a clear ‘slow component’ that was representative of n = 4 islets from Mouse 5 (period: 5.4±0.1 minutes). (C–D) The variation in the period of [Ca²⁺]_i oscillations indicates distinct differences from mouse to mouse for the inbred B6 strain (C) and the outbred CD-1 strain (D), as shown by one-way ANOVA (p<1.0e-24). Boxes drawn around Mouse 6 and Mouse 5 in (C) are described above.</p