Research matters

Endocrinology

Study identifies pathway required for normal reproductive development

Massachusetts General Hospital (MGH) clinical researchers, in collaboration with basic scientists from the University of California, Irvine, (UC Irvine) have identified a new molecular pathway required for normal development of the reproductive, olfactory and circadian systems in both humans and mice. In their report in the Proceedings of the National Academy of Sciences, the team describes defects in a gene called PROK2 (prokineticin 2) in human siblings with two different forms of infertility. The UC Irvine team had previously reported that mice lacking PROK2 had abnormal olfactory structures and disrupted circadian rhythm. The paper received early online release.

"We have demonstrated that PROK2 signalling is a novel pathway that is critical to the development of neurons that control the reproductive system, findings that should enable better understanding of human reproduction," says lead author Nelly Pitteloud, MD, of the Reproductive Endocrine Unit in the MGH Department of Medicine.

The current study is the latest in a series of investigations by the MGH group into the genetic basis of idiopathic hypogonadotropic hypogonadism (IHH), a rare condition in which puberty does not take place naturally. IHH occurs when a structure in the brain called the hypothalamus fails to develop neurons that secrete gonadotropin-releasing hormone (GnRH), a major controller of the reproductive system. Several genes involved in IHH have been discovered by the MGH investigators and others throughout the world; however, only 30% of IHH cases can currently be attributed to a known gene defect.

The investigation focused on PROK2, a protein known to regulate the development of the olfactory bulbs, the portion of the brain involved in the sense of smell, and to have a critical role in circadian rhythm in the mice. A form of IHH called Kallmann syndrome involves lack of both reproductive development and a sense of smell. PROK2's involvement in these systems led the researchers to investigate the protein's potential role in GnRH deficiency in human and mice.

The MGH team analysed the PROK2 genes of 100 study participants: 50 with Kallmann syndrome and 50 with IHH and a normal sense of smell. Three members from the same family in Portugal - two brothers and a sister - had identical defects in both copies of the PROK2 gene. Further study of this family revealed another brother with the mutation in only one PROK2 copy and a normal reproductive history. Five siblings of these individuals - now in their 70s - had died in infancy; similar early deaths have been seen in the PROK2-deficient mice. Interestingly, while the two affected brothers both had Kallmann syndrome, their affected sister had a normal sense of smell but did not experience normal puberty. "Until recently, IHH with a normal sense of smell and Kallmann syndrome with no sense of smell had been considered two distinct clinical entities," says Pitteloud, an assistant professor of Medicine at Harvard Medical School. "We now have described several kindreds in which different family members exhibit both syndromes yet harbour the identical mutation. So, it looks like additional gene defects or environmental cues modify how these syndromes develop in affected families.

The UC Irvine team was led by Qun-Yong Zhou, PhD, a professor of Pharmacology in its School of Medicine. His group has made fundamental contributions to the understanding of the neurobiological functions of prokineticin and its receptors. Their analysis of the reproductive status of mice lacking functional copies of Prok2 gene revealed that the animals' reproductive defect is due to the abnormal migration of neurons that secrete GnRH.

"Many recessive human genetic disorders, particularly the ones that have associated infertility symptom, are very difficult or almost infeasible to investigate using genetic analysis. The current study provides an elegant example how mouse studies can pinpoint the underlying genetic cause for human IHH disorders." says Zhou.

Genomics

Massive microRNA scan uncovers leads to treating muscle degeneration

Researchers have discovered the first microRNAs--tiny bits of code that regulate gene activity--linked to each of 10 major degenerative muscular disorders, opening doors to new treatments and a better biological understanding of these debilitating, poorly understood, often untreatable diseases. The study, published by the Proceedings of the National Academy of Sciences in November, was led by Iris Eisenberg, PhD, and Louis Kunkel, PhD, director of the Program in Genomics at Children's Hospital Boston and an investigator with the Howard Hughes Medical Institute.

The disorders, which cause muscle weakness and wasting, include the muscular dystrophies (Duchenne muscular dystrophy, Becker muscular dystrophy, limb girdle muscular dystrophies, Miyoshi myopathy, and fascioscapulohumeral muscular dystrophy); the congenital myopathies (nemaline myopathy); and the inflammatory myopathies (polymyositis, dermatomyositis, and inclusion body myositis). While past studies have linked them with an increasing number of genes, it's still largely unknown how these genes cause disease, and, more importantly, how to translate the discoveries into treatments.

For instance, most muscular dystrophies begin with a known mutation in a "master gene," leading to damaged or absent proteins in muscle cells. In Duchenne and Becker muscular dystrophies, the absent protein is dystrophin, as Kunkel himself discovered in 1987. Its absence causes muscle tissue to weaken and rupture, and the tissue becomes progressively non-functional through inflammatory attacks and other damaging events that aren't fully understood.

"The initial mutations do not explain why patients are losing their muscle so fast," says Eisenberg. "There are still many unknown genes involved in these processes, as well as in the inflammatory processes taking place in the damaged muscle tissue.

She and Kunkel believe microRNAs may help provide the missing genetic links. Their team analyzed muscle tissue from patients with each of the ten muscular disorders, discovering that 185 microRNAs are either too abundant or too scarce in wasting muscle, compared with healthy muscle. Discovered in humans only in the past decade, microRNAs are already known to regulate major processes in the body.

Therefore, Eisenberg believes microRNAs may be involved in orchestrating the tissue death, inflammatory response and other major degenerative processes in the affected muscle tissue. The researchers used bioinformatics to uncover a list of genes the microRNAs may act on, and now plan to find which microRNAs and genes actually underlie these processes.

The findings raise the possibility of slowing muscle loss by targeting the microRNAs that control these "cascades" of damaging events. This approach is more efficient than targeting individual genes. The team also defined the abnormal microRNA "signatures" that correspond to each of the ten wasting diseases. They hope these will shed light on the genes and disease mechanisms involved in the most poorly understood and least treatable of the degenerative disorders, such as inclusion body myositis. "At this point, it's very theoretical, but it's possible," says Eisenberg.

Pathology

Immune defect makes gut bacteria turn bad

In a striking new mouse model, an immune system glitch converts mild-mannered intestinal bacteria into a pathological army that inflames the host's colon and spreads the problem to normal mice.

The findings emphasize the importance of the interplay among the gut, its microbes, and its immune squad. The model opens new avenues to study inflammatory bowel disease and to test potential new therapies for people, said senior author Laurie Glimcher, the Irene Heinz Given professor of immunology at HSPH, and her colleagues. The study appeared in the Oct. 5 Cell.