Hypoxia: Problems and Scientific Challenges Prof. Rudolf Wu School - - PowerPoint PPT Presentation

Hypoxia: Problems and Scientific Challenges

• Prof. Rudolf Wu

School of Biological Sciences The University of Hong Kong (rudolfwu@hku.hk)

Hypoxia: An Old Problem with New Insights

Hypoxia: Trend

During the last few decades, anthropogenic input of nutrients into our coastal environment has increased ca. three folds, and is expected to double or triple if no action is taken

Hypoxia: Trend

Decrease in dissolved oxygen recorded over large coastal areas worldwide (including USA, China, Norway, UK, Sweden, Germany, Denmark, the Black Sea, Adriatic Seas) in the last 30-80 years

Diaz & Rosenberg, 1995; Rabalais, 2001

Total area>245,000 km2

Number of Dead Zones doubled every 10 years since the 1960s

Diaz & Rosenberg, 2008

Hypoxia Has Caused Major Changes in Structure and Functions of Ecosystems

– Mass mortality of fish and benthos – Changes in species composition – Changes in trophic relationships – Decrease in biodiversity and species richness – Decrease in fisheries production

Phil, 1994; Wu, 2002; Gray et al., 2002 Wu, 2002; Gray et al., 2002

Normoxia Hypoxia

Diversity, Species richness Demersal fish Larger body size Predator Suspended feeders

Deposit feeders Meiofauna, Nanoplankton Pelagic fish Short life cycle

Generalized Changes in Structure and Functions of Ecosystems

Wu, 2002

New Scientific Evidence further show that…..

Hypoxia is an endocrine disruptor

Common carp (Cyprinus carpio)

Male

0.1 0.2 0.3 7.0 mg/L 1.0 mg/L

***

(ng/ml) ** p<0.01; *** p<0.001

Wu et al, 2003

1 2 3 4 5 6 7 8 9 10 7.0 mg/L 1.0 mg/L

Estradiol Testosterone

**

Female

2 4 6 8 10 Testosterone Estradiol 7.0 mg/L 1.0 mg/L

*** *

(ng/ml) * p<0.05; *** p<0.001 Wu et al, 2003

• Gonadal

development

• Gametogenesis
• Spawning
• Fecundity

Hypoxia impairs fish reproduction

• Fertility
• Gamete quality
• Offspring survival
• Reproductive behavior

Common carp (Wu et al. 2003) Zebrafish (Shang et al. 2006) Atlantic croaker (Thomas et al. 2006,2007) Gulf killifish (Landry et al. 2007)

Sperm Motility

10 20 30 40 50 60 70 80 7 mg/L 1 mg/L

Curvilinear velocity Straight Line velocity Actual Path velocity

* * *

* p < 0.05

µmS-1

Wu et al, 2003

Reproductive Impairment

10 20 30 40 50 60 70 80 90 100 7 mg/L 1 mg/L Fertilization Hatching Larval Survival Egg to Larvae

*** *** *** ***

*** p < 0.001

%

Wu et al, 2003

Follow-up questions: What caused the

• bserved endocrine disruption?
• A smaller gonad and reduced hormone production

due to reduced energy intake and reduced growth?

• Hypoxia affects synthesis and metabolism of sex

hormones?

• Hypoxia affects GnRH and gonadotropins?

In vitro evidence

• In vitro studies using

H295R human adrenocortical carcinoma cell line and primary cell culture of medaka gonads

Cholesterol CYP11A Pregnenolone 3β-HSD

Progesterone CYP21 11-Deoxy-corticosterone

CYP11B1

Corticosterone CYP11B2 Aldosterone CYP17

17α-OH- Pregnenolone 3β-HSD

CYP17

17α-OH- Progesterone

CYP21

11-Deoxycortisol

CYP11B1

Cortisol

CYP17

DHEA 3β-HSD

CYP17

Androstene-dione 17β-HSD Testosterone CYP19 17β-Estradiol

Zona glomerulosa Zona fasciculata Zona reticularis

StAR

Hypoxia is a teratogen

Zebrafish (Danio rerio)

Hypoxia delays development

24hpf Control Hypoxia (0.5mg/l) 48hpf

Shang & Wu, 2004

Hypoxia caused spine and cardiac malformations

Shang & Wu, 2004

5 10 15 20 48h 72h 96h 120h 168h

Malformation (%) Time (hour)

* p < 0.05; ** p < 0.01

5.8 mg/L 0.8 mg/L

* ** **

Under hypoxia, apoptosis concentrates in the head but not the tail

Control Hypoxia

Shang & Wu, 2004

Sex differentiation/ reversal completed Final maturation

• f the

gonads Gonads differentiate into ovaries Spawning Sex differentiation begins 3β-HSD (-) CYP11A (-) CYP19A (ND) CYP19B (-) 3β-HSD (-) CYP11A (-) CYP19A (-) CYP19B (-) Male 3β-HSD (-) CYP11A (-) CYP19A (+) CYP19B (+) T/E2 (NC) Male 3β-HSD (-) CYP11A (-) CYP19A (-) CYP19B (NC) T/E2 (NC) Female 3β-HSD (+) CYP11A (-) CYP19A (+) CYP19B (+) T/E2 (+) Female 3β-HSD (-) CYP11A (-) CYP19A (+) CYP19B (NC) T/E2 (+)

(C) 60 dpf (D) 120 dpf (B) 40 dpf (A) 10 dpf

10-12 dpf 23-25 dpf 42 dpf 60 dpf 120 dpf

Juvenile Adult Larval

3 dpf 90 dpf 30 dpf

Shang et al, 2006

Normoxia Hypoxia 74.4% 61.9% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% in F1

male female

Hypoxia tips sex balance & favors a male biased population

***

*** p < 0.001

Shang, Yu & Wu, 2006

Where the girls are?

Will this affect reproductive success of the natural population?

Is the observed male biased phenotypic or geneotypic? Will the same happens to species with XY chromosomes?

Phenotypic & gonadal Sex in genotypic females (O. latipes) are altered by hypoxia

Cheung, 2006; Wu, 2009

Will the same occur in higher vertebrates?

• Salamanders (Ambystoma sp.): delayed

development and hatching, less developed and deformed embryos

• Australian frog (Crinia georgiana): delayed

embryonic development, increased malformation

• Male albino rats: reduced numbers of sertoli

cells and Leydig cells in testis

• Male Wistar rats: lower levels of LH and

testosterone

Seymonr et al., 2000; Shevantaeva & Kosyuga, 2006; Farias et al., 2007

Wu & Orr, 2005

7.50 4.50 3.50 20 40 60 80 100

A % copulation ***

7.50 4.50 3.50 2 4 6 8 10

B No.of offspring ***

7.50 4.50 3.50 0.0 0.5 1.0

C

Dissolved oxygen (mg O2 L-1)

• No. of broods

***

7.50 4.50 3.50 10 20 30 40 50

***

D Dissolved oxygen (mg O2 L-1)

Fecundity *** p<0.005

Methyl farnesoate?

Ecdysteroid?

Will the same occur in invertebrates?

Is the situation getting better or getting worse?

The situation is likely to get worse because…..

• Growth of treatment facilities is unlikely to catch up

with growth of population and industry, especially in developing counties

• Contributions from atmospheric fallout and non-

point source are significant

• Trans-boundary issues are difficult to resolve

Increase Temperature Increase freshwater input Increase nutrient flux Increase stratification Nutrient enrichment Enhanced productivity Global Warming

Hypoxia

Sediment

Increase metabolic rate

Risk Assessment

• Ecological consequence

Very serious

• Area affected

Very large

• Socioeconomic loss

Very big

• No. people affected

Very large

• Probability of occurrence

Very high

• Trend

Getting worse The new scientific evidence presented here calls for an urgent re-assessment of this old problem

Will the same happen in humans?

• Patients suffering from sleeping apnea have lower sex

drive and testosterone level (Saaresranta & Polo, 2003)

• Sex ratio in human depends on level of sex hormones
• f father and mother during conception, and high

testosterone level during conception favors subsequent birth of sons (James, 2004)

Brain Pituitary Ovary Blood sGnRH FSHβ LHβ FSH-R HMGR Progestin ?

(+)?

Sum m ary of effects of hypoxia on The HPG axis in fem ale zebrafish

ER

GnRH FSH CYP19A E2

CYP1 9 A E2

(+)

Proposed Work

Collaborate with fisheries authorities and undertake a scientific global review, focusing on :

– Trend analysis (spatial and level in the last 50 years) – Changes in structure and trophodynamics of marine communities (plankton, benthos, fish) – Identification of sensitive groups (bioindicators)

Proposed Work

Collaborate with fisheries authorities and undertake a scientific global review, focusing on :

– Reproductive status and reproductive impairment of fish in hypoxic areas vs normoxic areas – Endocrine disruption, malformation, sex ratio – Deciphering effects of hypoxia from those caused by

• ther anthropogenic activities (chemicals) prevailing

simultaneously in the marine environment?? – Identifying information gaps and further studies

Hypoxia affects spermatogenesis

Normoxia Hypoxia

** p < 0.01; *** p < 0.001

1 2 3 4 5 6 7 8 9 SPG SPC SPD

*** *** **

common carp

• No. of cysts/lobule

10 20 30 40 50 60 70 SPG SPC SPD

*** *** ***

zebrafish

% of each stage in testis

Wu et al., 2003; Shang et al., 2006

50 100 150 200 250 300

Diameter (µm)/Lobule

***

common carp

Hypoxia Normoxia

10 20 30 40 50 60 70 Oo PreV Vit PreO

Ovarian cell stage % of each stage in oocyte

*** *** *** ***

zebrafish Shang et al., 2006; Thomas et al., 2007 Landry et al., 2007

0% 20% 40% 60% 80% 100% Control 2.7 mg/L 1.7 mg/L PNS CA PYS SYS TYS

% of oocytes

Atlantic croaker

Normoxia Hypoxia

*** p < 0.001

Hypoxia affects Oogenesis