The Role of Preproglucagon Peptides in Regulating β-Cell Morphology and Responses to Streptozotocin-induced Diabetes

Insulin secretion from β-cells is tightly regulated by local signaling from preproglucagon (Gcg) products from neighboring α-cells. Physiological paracrine signaling within the microenvironment of the β-cell is altered after metabolic stress, such as high-fat diet or the β-cell toxin, streptozotocin (STZ). Here, we examined the role and source of Gcg peptides in β-cell function and in response to STZ-induced hyperglycemia. We used whole body Gcg null (GcgNull) mice and mice with Gcg expression either specifically within the pancreas (GcgΔPanc) or the intestine (GcgΔIntest). With lower doses of STZ exposure, insulin levels were greater and glucose levels were lower in GcgNull mice compared with wild-type mice. When Gcg was functional only in the intestine, plasma glucagon-like peptide-1 (GLP-1) levels were fully restored but these mice did not have any additional protection from STZ-induced diabetes. Pancreatic Gcg reactivation normalized the hyperglycemic response to STZ. In animals not treated with STZ, GcgNull mice had increased pancreas mass via both α- and β-cell hyperplasia and reactivation of Gcg in the intestine normalized β- but not α-cell mass, whereas pancreatic reactivation normalized both β- and α-cell mass. GcgNull and GcgΔIntest mice maintained higher β-cell mass after treatment with STZ compared with control and GcgΔPanc mice. Although in vivo insulin response to glucose was normal, global lack of Gcg impaired glucose-stimulated insulin secretion in isolated islets. Congenital replacement of Gcg either in the pancreas or intestine normalized glucose-stimulated insulin secretion. Interestingly, mice that had intestinal Gcg reactivated in adulthood had impaired insulin response to KCl. We surmise that the expansion of β-cell mass in the GcgNull mice compensated for decreased individual β-cell insulin secretion, which is sufficient to normalize glucose under physiological conditions and conferred some protection after STZ-induced diabetes. NEW & NOTEWORTHY We examined the role of Gcg on β-cell function under normal and high glucose conditions. GcgNull mice had decreased glucose-stimulated insulin secretion, increased β-cell mass, and partial protection against STZ-induced hyperglycemia. Expression of Gcg within the pancreas normalized these endpoints. Intestinal expression of Gcg only normalized β-cell mass and glucose-stimulated insulin secretion. Increased β-cell mass in GcgNull mice likely compensated for decreased insulin secretion normalizing physiological glucose levels and conferring some protection after STZ-induced diabetes

Inflammatory responses to dietary and surgical weight loss in male and female mice

Abstract Background Weight loss by surgery or lifestyle changes is strongly recommended for obese individuals to improve metabolic health, but the underlying impairments that persist from a history of obesity remain unclear. Recent investigations demonstrate a persistent inflammatory state with weight loss and bariatric surgery, but the mechanism and impact are not fully understood. Additionally, these studies have not been performed in females although women are the majority of individuals undergoing weight loss interventions. Methods The goal of this study was to determine the sex differences in metabolically induced inflammation after dietary weight loss (WL) or bariatric surgery. Following a 60% high-fat diet (HFD) for 12 weeks, C57Bl/6j mice underwent either a dietary switch to normal chow for WL or vertical sleeve gastrectomy (VSG) and were evaluated 8 weeks after intervention. WL effects on myelopoiesis were further evaluated with bone marrow chimeras. Results Both sexes had a decrease in adiposity and total weight following WL or VSG intervention. With HFD, females had very little inflammation and no further increase with WL, but males had persistent inflammation even after WL despite metabolic improvement. Interestingly, after VSG, myeloid inflammation was increased in the livers of males and to a lesser extent in females. Conclusions These studies demonstrate that regardless of sex, it is critical to assess an individuals’ history of obesity rather than just rely on current weight status in medical decision-making. There are long-lasting effects on tissue inflammation in both sexes especially with surgical weight loss. Dietary change is overall most effective to improve meta-inflammation in obese males on its own or in combination with surgical weight loss.https://deepblue.lib.umich.edu/bitstream/2027.42/148527/1/13293_2019_Article_229.pd

An IP3R3- and NPY-expressing microvillous cell mediates tissue homeostasis and regeneration in the mouse olfactory epithelium.

Calcium-dependent release of neurotrophic factors plays an important role in the maintenance of neurons, yet the release mechanisms are understudied. The inositol triphosphate (IP3) receptor is a calcium release channel that has a physiological role in cell growth, development, sensory perception, neuronal signaling and secretion. In the olfactory system, the IP3 receptor subtype 3 (IP3R3) is expressed exclusively in a microvillous cell subtype that is the predominant cell expressing neurotrophic factor neuropeptide Y (NPY). We hypothesized that IP3R3-expressing microvillous cells secrete sufficient NPY needed for both the continual maintenance of the neuronal population and for neuroregeneration following injury. We addressed this question by assessing the release of NPY and the regenerative capabilities of wild type, IP3R3(+/-), and IP3R3(-/-) mice. Injury, simulated using extracellular ATP, induced IP3 receptor-mediated NPY release in wild-type mice. ATP-evoked NPY release was impaired in IP3R3(-/-) mice, suggesting that IP3R3 contributes to NPY release following injury. Under normal physiological conditions, both IP3R3(-/-) mice and explants from these mice had fewer progenitor cells that proliferate and differentiate into immature neurons. Although the number of mature neurons and the in vivo rate of proliferation were not altered, the proliferative response to the olfactotoxicant satratoxin G and olfactory bulb ablation injury was compromised in the olfactory epithelium of IP3R3(-/-) mice. The reductions in both NPY release and number of progenitor cells in IP3R3(-/-) mice point to a role of the IP3R3 in tissue homeostasis and neuroregeneration. Collectively, these data suggest that IP3R3 expressing microvillous cells are actively responsive to injury and promote recovery

Food Restriction Compromises Immune Memory in Deer Mice (\u3cem\u3ePeromyscus maniculatus\u3c/em\u3e) by Reducing Spleen-Derived Antibody-Producing B Cell Numbers

Immune activity is variable in many wild animals, despite presumed strong selection against immune incompetence. Much variation may be due to changes in prevalence and abundance of pathogens (and/or their vectors) in time and space, but the costs of immune defenses themselves may also be important. Induction of immune activity often increases energy and protein expenditure, sometimes to the point of compromising fitness. Whether immune defenses are expensive to maintain once they are generated, however, is less well appreciated. If so, organisms would face persistent challenges of allocating resources between immunity and other expensive physiological processes, which would mandate trade-offs. Mild food restriction (70% ad lib. diet) reduces secondary antibody responses in deer mice (Peromyscus maniculatus), functionally representing a cost of immune memory. In this study, we asked whether compromised immune memory was mediated by a decrease in size of the B cell population responsible for producing antibodies (i.e., spleen-derived B lymphocytes producing immunoglobulin G [IgG]). Two weeks of food restriction reduced total splenocytes, total splenic B lymphocytes (B220+ cells), and splenic B lymphocytes producing IgG (B220+/IgG+ cells) but did not affect body mass or two circulating antibody subclasses (IgG1 and IgG2a) in deer mice. These results further indicate that maintenance of immune memory is expensive and may be subject to trade-offs with other physiological processes

Food Restriction Compromises Immune Memory in Deer Mice (\u3cem\u3ePeromyscus maniculatus\u3c/em\u3e) by Reducing Spleen-Derived Antibody-Producing B Cell Numbers

Immune activity is variable in many wild animals, despite presumed strong selection against immune incompetence. Much variation may be due to changes in prevalence and abundance of pathogens (and/or their vectors) in time and space, but the costs of immune defenses themselves may also be important. Induction of immune activity often increases energy and protein expenditure, sometimes to the point of compromising fitness. Whether immune defenses are expensive to maintain once they are generated, however, is less well appreciated. If so, organisms would face persistent challenges of allocating resources between immunity and other expensive physiological processes, which would mandate trade-offs. Mild food restriction (70% ad lib. diet) reduces secondary antibody responses in deer mice (Peromyscus maniculatus), functionally representing a cost of immune memory. In this study, we asked whether compromised immune memory was mediated by a decrease in size of the B cell population responsible for producing antibodies (i.e., spleen-derived B lymphocytes producing immunoglobulin G [IgG]). Two weeks of food restriction reduced total splenocytes, total splenic B lymphocytes (B220+ cells), and splenic B lymphocytes producing IgG (B220+/IgG+ cells) but did not affect body mass or two circulating antibody subclasses (IgG1 and IgG2a) in deer mice. These results further indicate that maintenance of immune memory is expensive and may be subject to trade-offs with other physiological processes

The release of neurotrophic factor NPY following injury simulation is mediated by a purinergic receptor, phospholipase C, and IP3/IP3 receptor pathway.

<p>(A) P2X_1,7 and P2Y₂ receptors mediate NPY release. Neonatal OE slices from Swiss Webster mice were incubated with vehicle (0.2% DMSO), non-selective P2 purinergic receptor agonist (ATP, 50 µM), P2X_1,7 agonist (BzATP, 50 µM), P2Y_2,4,6 agonist (UTP, 50 µM) or P2X_1,2/3,3 agonist (αβ-MeATP, 50 µM) for 1 hour and the levels of NPY in media were measured by ELISA. *, p<0.05 vs. vehicle (one-way ANOVA followed by Newman-Keuls post-hoc test; n = 6, 4, 4, 4 and 3 replications, respectively.) (B) ATP-induced NPY release is PLC- and IP3 receptor-dependent. Neonatal OE slices from Swiss Webster mice were pre-incubated with vehicle (0.2% DMSO), PLC inhibitor (U73122, 100 µM), or IP3 receptor inhibitor (2-APB, 100 µM) for 45 min prior to addition of vehicle (0.2% DMSO) or ATP (50 µM). Media was collected after 1 hr and the levels of NPY in media were measured by ELISA. *p<0.01 vs. vehicle; #p<0.05 vs. ATP (two-way ANOVA followed by Newman-Keuls post-hoc test; n = 6, 4, 4, 4, 5 and 5 replications, respectively.) (C) IP3 induces NPY release. Neonatal OE slices from Swiss Webster mice were incubated with vehicle (0.09% pluronic acid +0.45% DMSO) or caged iso-IP3/PM (caged IP3, 1.5 µM) and slices were illuminated with unfiltered light from a xenon arc lamp (30 min) to uncage IP3. Media was collected 1 hr later and the levels of NPY were measured by ELISA. p = 0.02 (Student’s t-test; n = 3 and 4 replications.).</p

IP3R3^−/− mice have fewer basal cells but a normal rate of proliferation in the OE.

<p>(<b>A–L</b>) Representative immunoreactivity to cellular markers in adult C57BL/6 (A, C, E, G, I, K) and IP3R3^−/− (B, D, F, H, J, L) mice: (A–B) horizontal basal cell marker cytokeratin 5 (CK5), (C–D) proneural transcription factor MASH1, (E–F) immature neuronal marker GAP43, (G–H) mature neuronal marker OMP, (I–L) proliferation cell marker PCNA and BrdU. DAPI (blue) demarcates the nuclei. Scale bar, 10 µm, shown in A is relevant for A–I. (<b>M</b>) The number of CK5⁺ HBCs, MASH1⁺ progenitor cells and GAP43⁺ immature neurons in the OE of IP3R3^−/− mice are significantly reduced. *, p<0.01 vs. respective control in C57BL/6 (Student’s t-test for each cell marker; n = 9–12 sections from 3–4 mice. Refer to legend in (O) for (M–O). (<b>N</b>) The number of OMP⁺ neurons in the OE of IP3R3^−/− is similar to C57BL/6 mice (p = 0.39, Student’s t-test; n = 9–12 sections from 3–4 mice.) (<b>O</b>) The rate of proliferation measured by PCNA expression and BrdU incorporation is comparable in the OE of IP3R3^−/−, IP3R3^+/− and C57BL/6 mice. p>0.05, Student’s t-test and one way ANOVA, respectively; n = 9–12 sections from 3–4 mice. Legend refers to M–O.</p