El gen RCAN1 y la EH

La sobreexpresión del gen podría resultar en un tratamiento para la Enfermedad de Huntington.

Mientras la investigación básica sobre la Enfermedad de Huntington continúa, aprendemos cada vez más sobre lo que funciona mal en la célula y en el cerebro. El desafío es entender qué patologías son significativas y a la vez un blanco para tratamiento. 

Investigadores de la Universidad del Sur de California descubrieron que los niveles de la proteína RCAN1-1l están dramáticamente reducidos (en un 70%) en el cerebro de los pacientes fallecidos con la EH comparados a los niveles de los individuos control que fallecidos de otras causas.

Este no es un descubrimiento sorprendente. Se sabe que la proteína de la EH ocasiona irregularidades en la transcripción genética, lo que da como resultado que ciertas proteínas sean reguladas hacia la alza y otras hacia la baja. Sin embargo, los investigadores tienen la sensación de que la regulación hacia la baja de éste gen en particular podría jugar un rol mayor en la patología de la EH.

En un modelo con células de la EH, utilizaron un vector viral para agregar el gen RCAN1-1l. Las células fueron rescatadas gracias a esta sobreexpresión del gen, dando lugar a la esperanza de que futuras investigaciones soporten la idea de que la sobreexpresión de RCAN1-1l pueda resultar en un tratamiento.

Los investigadores sugirieron que el mecanismo por el cual la regulación hacia la alza de RCAN1-1l ejerce un efecto positivo es mediante la inhibición del calcineuron. Se sabe que este gen regula hacia la baja la calcineurina, una enzima que modifica proteínas al remover fosfatos. Investigaciones anteriores han demostrado que fosforilar la proteína de la EH en una serina particular resulta ser una acción neuroprotectora. La disminución de RCAN-11l podría permitir que la calcineurina opere sin ser  controlada y que la proteína de la EH sea más tóxica.  

Sin embargo, otros investigadores hallaron que inhibir la calcineurina de hecho aceleró la enfermedad en el ratón R6/2. Qué es lo que da cuenta de la diferencia en estos diferentes descubrimientos? Podría ser que lo que funciona en un modelo con células no funcione en organismos vivientes o que los descubrimientos sean de hecho reconciliables si tanto demasiada como muy poca calcineurina resultan ser dañinas. Es claro que se necesita más trabajo, pero los descubrimientos actuales resultan intrigantes y necesitan ser explorados en mayor profundidad en ratones con la EH.

 

Referencia Adicional:

David Hernandez-Espinosa and A. Jennifer Morton. "Calcineurin inhibitors cause an acceleration of the neurological phenotype ina mouse transgenic for the human Huntington's disease mutation." Brain Research Bulletin 2006 May 31;69(6):669-79.

Marsha Miller, Ph.D.
lvin J. A. Davies
lvin J. A. Davies

Kelvin J. A. Davies, Ph.D., D.Sc.
James E. Birren Profesor de Gerontología,
y Profesor de Biología Molecular y Computacional.

El regulador de calcinerina (RCAN1-1L) es deficiente en la enfermedad de Huntington y protector contra la toxicidad de la huntingtina mutante in vitro

Gennady Ermak, Karl J. Hench, Kevin T. Chang, Sean Sachdev, and Kelvin J. A. Davies

Press release

New hope for treatment of neurodegenerative disorder: USC researchers uncover clues about cause of Huntington's disease

Los Angeles – Researchers from the University of Southern California have taken an important first step toward protecting against Huntington disease using gene therapy.

Huntington Disease is an incurable neurological disorder characterized by uncontrolled movements, emotional instability and loss of intellectual faculties. It affects about 30,000 people in the United States, and children of parents with the disease have a 50 percent chance of inheriting it themselves.

"Our findings allow for the possibility that controlled over-expression of RCAN1-1L might in the future be a viable avenue for therapeutic intervention in Huntington disease patients," said Kelvin J. A. Davies, professor of gerontology in the USC Davis School of Gerontology and professor of biological sciences in the USC College of Letters, Arts and Sciences.

In a paper in the June 2009 issue of Journal of Biological Chemistry, now available online, Davies and his coauthors use cell culture findings to show that a form of the gene RCAN1, known as RCAN1-1L, is dramatically decreased in human brains affected by Huntington disease. RCAN1-1L was first discovered in Davies' lab.

The investigators also show that increasing levels of RCAN1-1L rescues cells from the toxic effects of Huntington disease, a result that could someday lead to new avenues of treatment, according to Davies.

"Our discovery offers real hope and may even have wide-ranging implications for a variety of other important CAG repeat-related diseases," Davies said.

While the Huntington gene, which makes the normal Huntington protein, is an essential component to healthy nerve cells, the mutant Huntington gene makes a toxic mutant Huntington protein. Mutant Huntington contains increased levels of the amino acid glutamine, which is generated by a repetition of the DNA triplet CAG.

A normal Huntington gene has a sequence of between six and 34 CAG repeats. Any strand of DNA possessing more than 40 CAG repeats indicates the carrier will develop Huntington disease, according to the researchers.

Indeed, the more repeats of CAG, the earlier the disease manifests itself and the more devastating the disease becomes. Currently available drugs do little more than help control erratic movements associated with the condition.

"It is important to keep in mind that these protective findings are in-vitro, meaning in cell cultures. Further proof of protection by RCAN1-1L will be required in-vivo, or in actual Huntington disease patients," said lead author Gennady Ermak, research associate professor at the USC Davis School of Gerontology.

Previous in-vitro research has revealed that adding the phosphate PO4, an inorganic chemical, to the mutant Huntington protein can protect against the mutant gene. This process is called phosphorylation, and can be achieved by either inhibiting an enzyme (calcineurin) or by activating an enzyme (Akt).

"Our findings point to increased phosphorylation of mutant Huntington through calcineurin inhibition as the likely mechanism by which RCAN1-1L may be protective against the mutant Huntington," Ermak said.

As Davies explained: "RCAN1-1L may actually play a role in the cause of Huntington disease."

"The gene is required to down-regulate the activity of calcineurin. We have previously linked too much RCAN1-1L expression to Alzheimer's disease," Davies said. "Thus, Alzheimer's disease and Huntington disease appear to involve opposite problems with RCAN1 expression and calcineurin activity."

In cases of Huntington disease, too little RCAN1-1L may allow calcineurin to act unopposed and remove too many phosphates from the mutant Huntington protein.

"We observed complete protection against the mutant Huntington by RCAN1-1L," Ermak said, but he reiterated the need for further research with Huntington disease patients.

The results offer a new direction for further research, Davies added.

abstract

Our work suggests an important new link between the RCAN1 gene and Huntington disease. Huntington disease is caused by expansion of glutamine repeats in the huntingtin protein. How the huntingtin protein with expanded polyglutamines (mutant huntingtin) causes the disease is still unclear, but phosphorylation of huntingtin appears to be protective. Increased huntingtin phosphorylation can be produced either by inhibition of the phosphatase calcineurin or by activation of the Akt kinase. The RCAN1 gene encodes regulators of calcineurin, and we now demonstrate, for the first time, that RCAN1-1L is depressed in Huntington disease. We also show that RCAN1-1L overexpression can protect against mutant huntingtin toxicity in an ST14A cell culture model of Huntington disease and that increased phosphorylation of huntingtin via calcineurin inhibition, rather than via Akt induction or activation, is the likely mechanism by which RCAN1-1L may be protective against mutant huntingtin. These findings suggest that RCAN1-1L "deficiency" may actually play a role in the etiology of Huntington disease. In addition, our results allow for the possibility that controlled overexpression of RCAN1-1L in the striatal region of the brain might be a viable avenue for therapeutic intervention in Huntington disease patients (and perhaps other polyglutamine expansion disorders).

Our work suggests an important new link between the RCAN1 gene and Huntington disease. Huntington disease is caused by expansion of glutamine repeats in the huntingtin protein. How the huntingtin protein with expanded polyglutamines (mutant huntingtin) causes the disease is still unclear, but phosphorylation of huntingtin appears to be protective. Increased huntingtin phosphorylation can be produced either by inhibition of the phosphatase calcineurin or by activation of the Akt kinase. The RCAN1 gene encodes regulators of calcineurin, and we now demonstrate, for the first time, that RCAN1-1L is depressed in Huntington disease. We also show that RCAN1-1L overexpression can protect against mutant huntingtin toxicity in an ST14A cell culture model of Huntington disease and that increased phosphorylation of huntingtin via calcineurin inhibition, rather than via Akt induction or activation, is the likely mechanism by which RCAN1-1L may be protective against mutant huntingtin. These findings suggest that RCAN1-1L "deficiency" may actually play a role in the etiology of Huntington disease. In addition, our results allow for the possibility that controlled overexpression of RCAN1-1L in the striatal region of the brain might be a viable avenue for therapeutic intervention in Huntington disease patients (and perhaps other polyglutamine expansion disorders).