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News From The Journal Of Clinical Investigation: May 24, 2013

Malnutrition exacerbates Giardia infection in mice

Giardia is a common parasite that frequently infects young children in the developing world. It is commonly encountered through contaminated food, soil, or water. The parasite lives inside the intestines and can cause severe diarrhea and other gastrointestinal problems and Giardia infection has been associated with developmental growth delays. Because the majority of infected individuals do not experience symptoms and frequently are infected with other pathogens, it is unclear if endemic Giardia directly stunts growth. In this issue of the Journal of Clinical Investigation, Luther Bartelt and colleagues at the University of Virginia studied the effect of Giardia infection in a malnourished host. Malnourished mice exposed to Giardia developed a worse symptoms, including inflammation, intestinal damage, and growth retardation. These findings suggest that malnourishment puts children at greater risk for symptomatic Giardia infection. In the related Attending Physician piece, Theodore Nash describes how this single infectious agent can have dramatically different effects depending on an individual’s health history. As Herbert DuPont explains in the accompanying commentary, although preexisting nutritional state undoubtedly plays a role, the varying Giardia strains and host genetics are likely also contributors to the extent of disease.

TITLE: Persistent G. lamblia impairs growth in a murine malnutrition model


ACCOMPANYING COMMENTARY TITLE: Giardia: both a harmless commensal and a devastating pathogen


ACCOMPANYING THE ATTENDING PHYSICIAN TITLE: Unraveling how Giardia infections cause disease


Friendly bacteria tamp down the host immune response

Pathogenic bacteria typically elicit a host immune response; however, each of us lives with millions of strains of friendly bacteria (known as commensals) that do not activate the immune system or cause any symptoms. In this issue of the Journal of Clinical Investigation, researchers led by Catharina Svanborg at Lund University in Sweden propose that commensal bacteria act as guardians of their host environment, controlling the quantity and quality of host gene expression in order to prevent an immune response. To study these responses, Svanborg and colleagues used a strain of E. coli that colonizes the urinary tract but does not cause urinary tract infection symptoms. They found that, unlike bacteria that cause symptoms, the asymptomatic bacteria prevented the activation of inflammatory immune responses. This study identifies a mechanism by which commensal bacteria may establish a beneficial relationship with their host. In an accompanying Attending Physician article, Patrick Seed discusses how commensal bacteria could potentially be used as therapeutics in patients with recurrent urinary tract infections.

TITLE: Bacterial control of host gene expression through RNA Polymerase II


ACCOMPANYING THE ATTENDING PHYSICIAN TITLE: Anger management: bacteria soothe the savage host


Familial kidney disorder reveals inner workings of a portion of the immune system

C3 glomerulopathy refers to a group of kidney conditions characterized by innappropriate activation of an immune system response mechanism known as complement. Normally the complement system helps to clear pathogens from the body. It consists of a number of small proteins that, upon immune activation, are broken up into fragments that bind to foreign material or pathogen-infected cells to trigger their destruction. In C3 glomerulopathies, the complement fragments accumulate in the kidney, causing damage. In this issue of the Journal of Clinical Investigation, Santiago Rodríguez de Córdoba and colleagues at the Centro de Investigaciones Biológicas in Madrid, Spain identifed mutations in complement regulating protein, factor H, which increased complement activation. These studies help to define how factor H functions in complement regulation and provide a greater understanding of C3 glomerulopathy pathology. As Michael Holers of the University of Colorado explains in the accompanying commentary, variants in factor H genes are linked to multiple autoimmune and inflammatory diseases. Studies like this one may help to direct the development of new therapies.

TITLE: C3 glomerulopathy-associated CFHR1 mutation alters FHR oligomerization and complement regulation


ACCOMPANYING COMMENTARY TITLE: Human C3 glomerulopathy provides unique insights into complement factor H-related protein function


Bone-derived hormone and insulin influence male fertility

The bone cell-derived hormone osteocalcin promotes the production of testosterone in the mouse testis. Interestingly, osteocalcin-deficient mice exhibit increased levels of leutenizing hormone (LH), a pituitary hormone that regulates sex steroid synthesis in the testes. Additionally, osteocalcin levels appear to be linked to insulin secretion and sensitivity and circulating levels of testosterone in humans. In this issue of the Journal of Clinical Investigation, researchers led by Gerard Karsenty at Columbia University conducted a study to determine if LH and insulin regulate osteocalcin’s reproductive effects. Using transgenic mice, they found that osteocalcin and LH act in two parallel pathways to stimulate testosterone synthesis. To determine the importance of osteocalcin in humans, they analyzed patients with primary testicular failure, wherein the testes do not produce enough testosterone, and a mutation in a cellular receptor that allows Leydig cells in the testes to respond to osteocalcin. This study uncovers an endocrine axis that is necessary for optimal male fertility in the mouse and suggests that osteocalcin modulates reproductive function in humans.

TITLE: A pancreas-bone-testis axis and conservation of osteocalcin function in humans


Loss of RNA editing enzyme promotes melanoma growth

Dysregulated gene expression is a feature of most cancers. In this issue of the Journal of Clinical Investigation, Gal Markel and colleagues at Chaim Sheba Medical Center in Ramat-Gan, Israel, demonstrated that expression of the RNA editing enzyme ADAR1 is frequently reduced in melanoma that was linked to the development of metastases. Loss of ADAR1 enhanced the growth and tumor-forming ability of the melanoma cells. Markel and colleagues found that ADAR1 normally regulates the expression of microRNAs, molecules that help to control the expression of specific genes. In turn, microRNAs also control the expression of ADAR1. These studies demonstrate that loss of an RNA editing enzyme contributes to the development of a more aggressive, metastatic form of melanoma.

TITLE: MicroRNA-mediated loss of ADAR1 in metastatic melanoma promotes tumor growth



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