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Lactobacillus Plantarum Strain Mantains Growth of Infant Mice During Chronic Undernutrition
Main Idea:
In this paper, researchers were able to discover that micro-biota plays an essential role in growth development of juvenile rats. By comparing germ free mice and wild type mice in the same growth conditions, and then in nutrient-depleted conditions, researchers were able to observe that the microbiota has a significant affect in the maintenance of juvenile mouse growth, and more specifically maintenance of the somatotropic axis. Even more fascinating, introduction of bacterial strains to germ-free mice allows for maintenance of juvenile mouse growth and maintenance of the somatotropic axis.
My Opinion:
I really enjoyed reading this paper. I found the research was presented in an incredibly clear manner, and I also found the subject to be very fascinating. The paper was very well written. I thought the researchers were especially straight forward in telling the reader their hypothesis for each experiment, their methods, and then their main conclusions. They started with a basic experiment in looking at growth through weight and length, and then delved deeper through exploration of the somatotropic axis.
Figure 1
In Figure 1, researchers show the role of the microbiota in growth development of mice. The question the researchers want to answer in this experiment is whether or not the microbial composition of a mouse will affect the mouse’s juvenile development growth. To conduct an experiment in order to answer this, the researchers used wild type mice and germ free mice as their experimental groups. The experimental groups were both feed on a standard diet until 8 weeks of age (from 7 days after birth to 56 days after birth). Throughout this 8-week time period, weight and body length of both experimental groups were measured daily. At the end of the 8 week period (at 56 days), bone growth parameters of the femur bones were subsequently measured. As visible in the results of Figure 1, the researchers were able to extrapolate that the microbiota maintains predicted ideal weight gain and length due to the optimal weight gain and length of the wild type mice in comparison to the germ free mice.
Figure 2
In Figure 2, Researchers show the role of the microbiota in the somatotropic axis specifically, which is the foremost driver of postnatal growth. The question the researchers want to answer in this experiment is whether or not the microbial composition of a mouse will affect different aspects of its somatotropic axis, which is known to be incredibly important in the activation of juvenile growth. Replicating the same methods as in Figure 1, the researchers instead periodically measured levels of growth hormone, IGF-1, and IGFBP-3 in the serum of the two experimental groups of mice over the course of 8 weeks. At day 28 of the experiment, the researchers also measured levels of IGF-1 and IGFBP-3 in the liver of each experimental group, and used a western blot to quantify the phosphorylation of Akt at Ser 473 of each experimental group. It is important to note that in the somatotropic axis, the brain harvests growth hormone. This growth hormone induces IGF-1 and its binding protein IGFBP-3, which both determine growth. Phosphorylation of Akt at Ser 473 is a marker of IGF-1 signaling. Due to the high levels of IGF-1, IGFBP-3 and phosphorylation of AKT at Ser 473 in wild type mice, the researchers were able to deduct that the microbiota maintains somatotropic axis activity. Germ free mice, lacking a microbiota, have significantly less levels of these growth-inducing proteins, and therefor are unable to maintain their somatotropic axis activity.
Figure 3
In Figure 3, Researchers show the role of the microbiota and of different strains of L. plantarum in growth development of mice introduced to a nutrient-depleted diet. The researchers had two main questions when conducting this third experiment. The first is whether or not the microbiota will be able to maintain a nutrient-depleted diet. The second was, if introducing two different strains of L. plantarum, which are known as growth promoting strains in Drosophila, to germ-free mice, may in fact assist in maintaining growth. The same experiment as in Figure 1 was conducted, however, with the introduction of two new experimental groups. The first is a group of germ free mice introduced to of L. plantarumWJL (LpWJL) and the second is a group of germ free mice introduced to L. plantarumNIZ02877 (LpNIZ02877). This experiment was conducted with the added variable of exposing the same four experimental groups to either the original standard-fed diet, or a nutrient depleted diet. Throughout this 8-week time period, weight and body length of all four experimental groups in both variables of either standard fed, or nutrient depleted, were measured daily. At the end of the 8-week period (at 56 days), bone growth parameters of the femur bones were subsequently measured. Through the results in Figure 3, the researchers found that not only does the microbiota maintain growth during undernutrition, but also that certain strains of L. plantarum in germ-free mice can maintain the growth of the mice and resemble the maintained growth of wild-type mice.
Figure 4
In Figure 4, Researchers show the role of the microbiota and of different strains of L. plantarum in growth development of mice introduced to a nutrient-depleted diet in the somatotropic axis specifically. The question the researchers want to answer in this experiment is whether or not the microbial composition of a mouse or of different strains of L. plantarum in germ free mice will maintain different aspects of the somatotropic axis. Replicating the same methods as in Figure 2, the researchers periodically measured levels of growth hormone, IGF-1, and IGFBP-3 in the serum of the four experimental groups of mice fed nutrient deplete diets. In the results, the researchers concluded similar results as in Figure 3, that the microbiota is able to successfully maintain somatotropic axis activity during chronic under nutrition. Not only this, but certain strains of L. plantarum in germ-free mice (LpWJL) can maintain the activity of the somatotropic axis activity and resemble the maintained growth of wild-type mice. After this experiment, the researchers did a further experiment. Weight and body length of wild type mice in both variables of either standard fed, or nutrient depleted, were measured daily over 8 weeks with the added variable of either being injected with a control or with Cycloignan Compound (PPP) for 10 days of the 8 weeks. PPP is known to inhibit the IGF-1 from binding to its receptor. From these results, the scientists were able to deduce that even during a depleted diet, the microbiota is able to somewhat maintain the somatrotropic axix activity in growth. This data shows that it is essential to not only have enough of the IGF-1 and IGFBP-3 in the body, but it is also essential to have a working receptor for these proteins in order to have an active somatotropic axis.
Bibliography:
Schwarzer et. al. 2/19/2016. Lactobacillus Plantarum Strain Mantains Growth of Infant Mice During Chronic Undernutrition. Science [Internet]. [cited 20 April 2016]. Available from: http://science.sciencemag.org/content/351/6275/854.full
