Shedding Light on a Cell That May Contribute to Alzheimer’s and ALS

NEUROSCIENCE NEWSDECEMBER 9, 2016

Summary: New research could help scientist better understand the role of astrocytes in neurodegenerative diseases.

Source: UCLA.

The hippocampus of a mouse with the artificial Cre/ERT2 gene, showing astrocytes glowing green. Neurosciencenews image is credited to Baljit Khakh lab/David Geffen School of Medicine at UCLA.

An achievement by UCLA neuroscientists could lead to a better understanding of astrocytes, a type of cell in the brain that is thought to play a role in Lou Gehrig’s disease, also called amyotrophic lateral sclerosis, or ALS; Alzheimer’s disease; Huntington’s disease; and other neurological disorders.

The researchers are the first to have bred mice in which an artificial gene called Cre/ERT2, a basic tool for studying the functions of cells, can be activated exclusively in astrocytes. A paper describing their work was published online today in the journal Neuron.

Neuroscientists have been trying for years to engineer mice in which Cre/ERT2 or other artificial genes can be activated just in astrocytes without significant “leakage” into other cell types.

“We’ll now be able to delete or mutate astrocyte genes that are suspected of contributing to diseases such as ALS to see whether they really do contribute,” said Baljit Khakh, professor of physiology and neurobiology at the David Geffen School of Medicine at UCLA. “That, in turn, could open up many new strategies for treating those diseases.”

To give the mice the Cre/ERT2 gene, Khakh and colleagues inserted it into another gene, Aldh1-l1. Aldh1-I1 had been found in a previous study to only be active in adult astrocytes. 

Cre/ERT2 normally can be activated in mice by giving them a drug called tamoxifen, which is best known as a breast cancer treatment. The UCLA researchers, however, built the combination gene so that tamoxifen could only “turn on” the Cre/ERT2’s when it was in astrocytes. The researchers also verified that the gene becomes active in virtually all astrocytes in the adult mouse brain but in virtually no other cells.

Scientists have known that astrocytes perform a variety of routine functions throughout the brain, and it is believed that they have a major influence on how the brain works and how humans and other animals behave. But what scientists haven’t been able to explain very well is how, at the molecular level, astrocytes accomplish all of these functions.

The UCLA advance should provide a powerful tool that scientists can use to solve that puzzle.

“The availability of these mice makes possible experiments that I think will keep researchers busy for many years to come,” Khakh said.

In initial demonstrations, Khakh and his team used the mice to learn more about a phenomenon called “calcium signaling,” through which astrocytes influence the functions of neurons, and also to identify for the first time the genes that are normally active in adult mouse astrocytes.

Astrocytes have also been linked to several neurological diseases, including ALS, a usually fatal disease in which neurons that control muscles face progressive destruction. Several recent studies on ALS have identified astrocytes as a significant cause of the deaths of these neurons. How astrocytes end up harming neurons in ALS remains a mystery, but the mice with Cre/ERT2 should enable researchers to tackle that question more effectively than they could have before, Khakh said.

ABOUT THIS ALZHEIMER’S DISEASE RESEARCH ARTICLE

The study’s lead authors are Rahul Srinivasan, Tsai-Yi Lu and Hua Chai, of Khakh’s laboratory. Other co-authors are Ji Xu, Ben Huang, Peyman Golshani and Giovanni Coppola, all of UCLA. 

Funding: The study was supported by a grant from the National Institutes of Health.

Source: David Olmos – UCLA

Image Source: This NeuroscienceNews.com image is credited to Baljit Khakh lab/David Geffen School of Medicine at UCLA.

Original Research: Abstract for “New Transgenic Mouse Lines for Selectively Targeting Astrocytes and Studying Calcium Signals in Astrocyte Processes In Situ and In Vivo” by Rahul Srinivasan, Tsai-Yi Lu, Hua Chai, Ji Xu, Ben S. Huang, Peyman Golshani, Giovanni Coppola, Baljit S. Khakh in Neuron. Published online December 8 2016 doi:10.1016/j.neuron.2016.11.030

Abstract

New Transgenic Mouse Lines for Selectively Targeting Astrocytes and Studying Calcium Signals in Astrocyte Processes In Situ and In Vivo

Highlights

•Cre/ERT2 mice were made to achieve astrocyte-specific genetic manipulations in vivo

•Knockin Lck-GCaMP6f mice were made to study astrocyte calcium signals in vivo

•Mice were used to determine the adult cortical astrocyte transcriptome

•New, well-characterized, and much needed in vivo genetic resources are provided

Summary

Astrocytes exist throughout the nervous system and are proposed to affect neural circuits and behavior. However, studying astrocytes has proven difficult because of the lack of tools permitting astrocyte-selective genetic manipulations. Here, we report the generation of Aldh1l1-Cre/ERT2 transgenic mice to selectively target astrocytes in vivo. We characterized Aldh1l1-Cre/ERT2 mice using imaging, immunohistochemistry, AAV-FLEX-GFP microinjections, and crosses to RiboTag, Ai95, and new Cre-dependent membrane-tethered Lck-GCaMP6f knockin mice that we also generated. Two to three weeks after tamoxifen induction, Aldh1l1-Cre/ERT2 selectively targeted essentially all adult (P80) brain astrocytes with no detectable neuronal contamination, resulting in expression of cytosolic and Lck-GCaMP6f, and permitting subcellular astrocyte calcium imaging during startle responses in vivo. Crosses with RiboTag mice allowed sequencing of actively translated mRNAs and determination of the adult cortical astrocyte transcriptome. Thus, we provide well-characterized, easy-to-use resources with which to selectively study astrocytes in situ and in vivo in multiple experimental scenarios.

“New Transgenic Mouse Lines for Selectively Targeting Astrocytes and Studying Calcium Signals in Astrocyte Processes In Situ and In Vivo” by Rahul Srinivasan, Tsai-Yi Lu, Hua Chai, Ji Xu, Ben S. Huang, Peyman Golshani, Giovanni Coppola, Baljit S. Khakh in Neuron. Published online December 8 2016 doi:10.1016/j.neuron.2016.11.030

http://neurosciencenews.com/cre-ert2-alzheimers-als-5717/