ALDH1 and ALDH2, two faces of alcohol tolerance?

Alcoholic is a social problem in western countries but not in East Asian countries probably due to an enzyme difference for alcohol metabolism among the people. Aldehyde dehydrogenase (ALDH) is one of the key enzymes that degrade alcohol to acetic acid in the liver. There are two major isoenzymes of ALDH: ALDH1 and ALDH2. ALDH1 locates in cytosol and ALDH2 locates in mitochondria. Most Caucasians have both isoenzymes, but ~50% East Asians have normal ALDH1 and inactive ALDH2. Interestingly, low ALDH2 activity is associated with alcohol intolerance, whereas low ALDH1 activity is associated with alcoholic.  A recent paper in Science (Kim et al. (2015)) provides a possible explanation for this phenomena.

In the Science paper, the investigators elucidate an alternative pathway for GABA synthesis in midbrain dopaminergic neurons. The neurotransmission in midbrain dopaminergic neurons is essential to understand the mechanisms of Parkinson disease, a neurodegenerative disorder affecting many people. The investigators are interested in a puzzle that GABA and dopamine are co-released from dopaminergic neurons, but very few dopaminergic neurons express the classic GABA synthesis enzymes—glutamate decarboxylases (GAD65 and GAD67). Learning from another enzyme, ALDH, used by plant, frog, and glia cells to synthesize GABA, they had a hypothesis that ALDH is the enzyme for GABA synthesis in midbrain dopaminergic neurons.

First, they recorded the alterations in inhibitory postsynaptic currents (IPSC) in spiny projection neurons in the striatum of mice, which receive input signal (GABA) from midbrain dopaminergic neurons. By using GAD inhibitor or GAD knockout, they confirmed that the IPSC in spiny projection neurons are independent of GAD activity. In addition, they excluded the possibility that dopamine may activate GABA receptors on spiny projection neurons.

Next, based on previous knowledge that one isoenzyme of ALDH, ALDH1,  is cytosolic and highly expressed in the brain, they checked Aldh1a1 expression in midbrain and found it highly abundant in the terminals of midbrain dopaminergic neurons. Then they found the IPSC in spiny projection neurons were reduced with ALDH inhibitors or Aldh1a1 knockout, which supports the hypothesis that ALDH1 mediates the GABA synthesis in midbrain dopaminergic neurons.

At last, due to the association of Aldh1a1 with alcoholic and the involvement of dopaminergic system in alcoholic addiction, they continued to test the connection in a alcohol binge model in mice. They found binge drinking can reduce IPSC in spiny projection neurons, and Aldh1a1 knockout mice consume more alcohol than normal mice. It indicates that alcohol can inhibit GABA synthesis in midbrain dopaminergic neurons, and in people with ALDH1A1 variants, the GABA inhibition is abolished, which causes alcoholic behavior. 

Although both ALDH1 and ALDH2 are involved in alcoholic metabolism, ALDH1 is responsible for GABA synthesis in dopaminergic neurons, whereas ALDH2 is responsible for alcohol clearance. without ALDH1, you are more likely to be alcoholic; without ALDH2, you are more likely to be intolerable of alcohol. That said, ALDH2 is also highly expressed in the brain. Will ALDH2 variants affect the GABA synthesis and alcohol addiction? This is the limit of this paper.

“Neanderthal Man: In search of the lost genome" by Svante Pabbo

When I was a child, I was enchanted by the mysterious atmosphere of graveyards, hoping to see some skeletons, and know their lost stories. It seems I am not alone. Svante Pabbo, the Swedish molecular anthropologist is one of the most famous people to build a career on his childhood’s dream.

In a new memoir “Neanderthal Man: In search of the lostgenome", Svante Pabbo tells us a vivid story of how a curious and sentimental boy’s dream turns true. When he was a child, Svante Pabbo was attracted to Egyptian mummies and fascinated by their mysteries, hoping to solve the puzzles around the mummies one day. It was not until he was a graduate student that Svante Pabbo got the spark to analyze the genome of Egyptian mummies, when molecular biology started to boom in 1980s. Followed by a series of questions in 25 years, this initial maneuver led to his final success on sequencing the genome of Neanderthal man.

In the first chapter, Svante Pabbo described an eureka in 1996, when his student Matthias Krings decoded a fragment of the mitochondria DNA sequence from the DNA sample extracted from a 40000 years old Neanderthal Man that was excavated from the Neander Valley in Germany. He was so excited and cautious too that he did not open the champagne until he was confident with the results after several repeats. This breakthrough gave him confidence on decoding genes in ancient humans.

In the following chapters, Svante Pabbo tells his story in a chronological order, with logical questions step by step leading to the final answer. He first asked whether DNA could survive after tissue death. Answering this question, he heated the calf liver in the lab oven at 50 C for days, and got a few hundred nucleotides. Next, he asked how long the DNA could survive after tissue death. He obtained the samples of Egyptian mummies from East Germany through an anthropologist friend, and used nuclear dye to stain the cartilage and skin cells of the samples. After he found positive nuclear staining in these samples, he was sure the DNA is still there, he then extracted the DNA from these samples, and cloned the extraction into bacteria for sequencing. This experiment proved the preservation of DNA to as old as about 4000 years.

Contamination of modern DNA is the main concern of the whole business. Therefore, how to get rid of the contamination during the DNA extraction is the next question. Svante Pabbo and his students tried many ways to reduce the contamination to almost none, such as making a clean room with everything inside clean of DNA. They also developed some internal controls to solve this problem. Now the ancient DNA is cleared of contamination, they can continue to ask the next question: could 40000 years old Neanderthal man DNA be sequenced?

They first tried with a frozen Siberian mammoth about 50000 years old. If this works, the Neanderthal man will also work. They succeeded to get the mitochondrial DNA of this mammoth in 1994. Then they went on to extract DNA from Neanderthals. Now back to the scene in chapter one, they got lucky again and did get mitochondrial DNA of Neanderthals. Mitochondrial DNA has only a few hundreds nucleotides, whereas the nuclear genome has 6.4 billion nucleotides; thus, to see the big map of Neanderthal genome, they need to sequence the nuclear genome.

Most ancient DNA is degraded; therefore, it is not easy to get enough DNA to sequence nuclear DNA. Svante Pabbo examined Neandersal samples from several digging sites where the Neandersals were excavated. He could get very small amount of nuclear DNA from a few well-preserved Neandersal samples. Luckily, the DNA sequencing technology now makes it possible to use little DNA to sequence the whole genome. In 2010, Svante Pabbo and his group finally sequence the first Neandersal genome.

At last, the question comes to the human origin. Did Neandersals contribute DNA to modern human? Did modern human inbreed each other, and have gene flow to each other? By comparing the genomes of Neandersals with those of modern human of European, East Asian, African, American, and South Asian, Svente Pabbo found Neandersals shared more genetic variants with present-day humans in Europe than with present-day humans in Africa, and drew the conclusion that non-African modern human have 1-4% of their DNA originated from Neandersals 30000 years ago, when they met and inbred with each other in Middle East. After that short convention, Neandersals disappeared and modern human continued to migrate to the other part of the world and replaced the aboriginal ancient human.

Svante Pabbo’s writing is concise and logical; there is no jargon for laymen, and it is very easy to read.

Stir-fried chicken with pepper and tree fungus

Introduction:
It is an mix of meat and vegetables, and the flavor can diffuse to each other. The fungus becomes tasty with the flavor of chicken, and the chicken becomes fresher with the fragrance of pepper and fungus. The tree fungus is special for its chewer.

Ingredients:
500g chicken thighs
100g bell pepper
50g dry tree fungus
30 ml canola oil
10g bunching onion
10g ginger
10g garlic
5g sugar
5g salt
1g black pepper
1g potato starch

Preparation:
1. Cut chicken thighs into 4 cm x 4 cm pieces, put into cold water in pot, heat to boiling to remove the blood, drain the water and keep aside
2. Cut bell peppers into  4 cm x 4 cm pieces, and hydrate the tree fungus with hot water for 5 minutes
3. Chop the bunching onion, ginger, and garlic into small pieces
4. Heat the canola oil in a fry pan on the stove over high heat for 1 minute
5. Add the ginger, garlic, and bunching onion into the hot oil and stir for 1 minute
6. Add chicken thighs pieces into the pan and stir for 1 minute, then add pepper and tree fungus into the pan and stir for 1 minute
7. Add sugar, salt, and black pepper into the pan, and continue to stir for 5 minutes
8. Thicken with potato starch to finish

Stir-fried chicken heart with pepper

Introduction:
It is an easy-to-prepare dish based on the taste of chicken heart. You can add your favorite spices to adjust the final flavor. The fine texture of the heart makes it just right for chew, and the smooth muscle makes it tasty.

Ingredients:
500g chicken heart
100g bell pepper
30 ml canola oil
10g bunching onion
10g ginger
10g garlic
5g sugar
5g salt
1g black pepper
1g potato starch

Preparation:
1. Cut chicken heart into 0.5 cm thick slices, put into cold water in pot, heat to boiling to remove the blood, drain the water and keep aside
2. Cut bell pepper into 2 cm x 2 cm blocks
3. Chop the bunching onion, ginger, and garlic into small pieces
4. Heat the canola oil in a fry pan on the stove over high heat for 1 minute
5. Add the ginger, garlic, and bunching onion into the hot oil and stir for 1 minute
6. Add chicken heart pieces into the pan and stir for 1 minute, then add pepper blocks into the pan and stir for 1 minute
7. Add sugar, salt, and black pepper into the pan, and continue to stir for 5 minutes
8. Thicken with potato starch to finish

Three-cup chicken

Introduction:

This dish was said to originate from Jianxi in Song dynasty, and be modified in Taiwan to become very popular now in US. The original 3 cups include rice wine, pig fat, and soy sauce; the Taiwanese version includes rice wine, sesame oil, and soy sauce. This recipe is an integration of several popular recipes for three-cup chicken, with a special ratio of rice wine, soy sauce, and sesame oil as 4:2:1.

Ingredients:

500g chicken thighs

20ml sesame oil

10ml olive oil

45ml light soy sauce

15ml concentrated soy sauce

120ml rice wine (Shaoxing 17%)

20g bunching onion

20g Thai basil

20g ginger

20g garlic

5g sugar

1g salt

1g dry hot pepper

Preparation:

1. Cut chicken thighs into 4 cm x 4 cm pieces, put into cold water in pot, heat to boiling to remove the blood, drain the water and keep aside

2.Cut the bunching onion into 5cm long fragments, and ginger and garlic into 0.3 cm thick slices 

3. Heat the mixture of sesame oil and olive oil in a fry pan on the stove over high heat for 1 minute

4. Add the dry hot pepper and ginger into the hot oil and stir for 2 minutes or until they dark and dry, then add garlic and bunching onion, continue stirring for 1 minute

5. Add chicken thighs pieces into the pan and stir for 1 minute, then add the mixture of sugar, light and concentrated soy sauce, and rice wine

6. Heat over high heat until boiling and continue to heat with stir over mild heat for 20 or until the liquid dries

7. Add the thai basil 1 minute before the finish, with the lid covered

Stir-fried shrimp with loofah, tomato, and egg

Introduction:

It is a mixture of four different tastes: flavors of shrimp and egg, sourness of tomato, and fragrance of loofah.

Ingredients:

100g shrimp

200g loofah

100g tomato

2 eggs

60 ml canola oil

10g ginger

10g garlic

5g sugar

5g salt

1g black pepper

1g potato starch

Preparation:

1. Cut tomatoes into 1/8 slices

2. Remove the skin and seeds of loofahs and cut into 2 cm x 2 cm blocks

3. Chop the bunching onion, ginger, and garlic into small pieces

4. Heat 20ml canola oil in a fry pan on the stove over high heat for 1 minute, add two light-beating eggs into the pan, stir and take them out once they are solidified 

5. Heat 20ml canola oil in a fry pan on the stove over high heat for 1 minute, add the shrimps, flap and take them out once they turn pink 

6. Add the ginger, garlic, and bunching onion into the hot oil and stir for 1 minute

7. Add tomato and loofah blocks into the pan and stir for 1 minute

8. Add sugar, salt, and black pepper into the pan, and continue to stir for 3 minutes

9. Add the prepared eggs and shrimps into the pan and stir with the loofah and tomato for 3 minutes
10. Thicken with potato starch to finish

Ratatouille