Transcript Sex steroids vs sex chromosomes? - McMaster University`s Faculty

Chromosomes and Hormones:
Which Determine Structure and Function of the Brain
and Underlie Sex Differences in the Timing of Puberty?
Mark R. Palmert, M.D., Ph.D.
Division of Endocrinology
Genetics and Genome Biology Program
The Hospital for Sick Children
The University of Toronto
UNIVERSITY
of TORONTO
And we know sex differences exist in humans too!
How about a quiz…..
What do many 6 year olds with ADHD and Autism have in common?
Being male
What do many 17 year olds with Depression and Anxiety have in common?
Being female
What is a major difference between most 6 years with precocious puberty
and most 14 year olds with delayed puberty?
Precocious Puberty = females; delayed puberty = males
How Might Sex Differences Arise?
• Effects of sex steroids?
• Effects of X vs Y sex chromosomes, independent of gonadal differentiation?
• Effects of socialization and environment?
And by what mechanisms?
• Hormonal effects themselves?
• Gene dosage?
• X vs Y specific genes?
• Hormone induced epigenetic efffects?
Two Foci--Investigation of Sex-specificity
• Brain structure and function, where differences matter due to
differences in mental health outcomes
– M:F ratios for depression (1:3), autism (4:1), ADHD (3:1) Alzheimer disease (1:2)
– Males with higher rates of externalizing disorders with pre-pubertal onset; Females with
higher rates of internalizing disorders with post-pubertal onset.
• The timing of puberty, where differences matter due to clinical
presentations and associations with later life outcomes
– Girls tend to have earlier puberty and are more likely to have precocious puberty
– Boys tend to develop at later ages and are more likely to have delayed puberty
How Can Genetics and Animals Help Us?
Two
Types
1. Sex steroid effects
Organizational
effects
Ambient/
Activational
effects
How Can Genetics Help Us?
Two
Types
1. Sex steroid effects
2. Sex chromosomes
Organizational
effects
Ambient/
Activational
effects
Sex steroids vs sex chromosomes? 4CG
Ji H et al. Hypertension. 2010;55:1275-1282
Sex steroids vs sex chromosomes? 4CG
F vs. M
= hormonal
influence
XX vs. XY
= chromosomal influence
Adapted from McCarthy and Arnold, Nature Neurosci, 2011
MRI is Method Employed
7 Tesla Magnet.
16 mice imaged at once.
Females
100
80
60
40
XX F (n=40)
XY F (n=35)
20
0
26
28
30
32
34
36
% Animals with PS
% Animals with VO
Sexual maturation occurs
at the same rate in XX and XY 4CG mice
Males
100
80
60
40
XY M (n=45)
XX M (n=48)
20
0
26
28
pnd
Corre C et al, Brain Structure & Function, 2014
30
pnd
32
34
36
Cerebellar
Cortex
•
traditional motor feedback
structure.
•
strong evidence for role in
affect and cognition.
•
larger in females.
BNST
•
canonical sexually dimorphic
brain structure, larger in
males.
•
part of extended amygdala.
•
strong reciprocal connections
to hypothalamus.
•
integrates fear, reward, and
stress circuits.
Sex Steroids
and
Sex Chromosomes
Cause Male-Female
Differences
Corre C et al,
Brain Structure and Function, 2014
Sex Steroids
and
Sex Chromosomes
Cause Male-Female
Differences
Corre C et al,
Brain Structure and Function, 2014
Things Learned from Study of 4CG Model
1. Both sex steroids and sex chromosomes contribute to sex
differences in brain structure.
2. Sex chromosomes are seen in more areas than anticipated.
3. In nearly all sexually dimorphic regions, the effects of
chromosomes and hormones are distinct, with one or the
other leading to the sex differences in a particular region.
4. Different mechanisms lead to sex-specificity in different
regions.
Things Learned from Study of 4CG Model
1. Both sex steroids and sex chromosomes contribute to sex
differences in brain structure.
2. Sex chromosomes are seen in more areas than anticipated.
3. In nearly all sexually dimorphic regions, the effects of
chromosomes and hormones are distinct, with one or the
other leading to the sex differences in a particular region.
4. Different mechanisms lead to sex-specificity in different
regions.
5. Question--Is there a chance sex steroids mask influences of
sex chromosomes?
Gonadectomy reveals effect of chromosomes
on BNST volume
Corre C et al, Unpublished
Gonadectomy reveals effect of chromosomes
on BNST volume
Corre C et al, Unpublished
Structure, sure. But what about function?
Behavior Studies--Ambient Hormone Effects
Behavior Studies--Ambient Hormone Effects
Hippocampus
•
key region for integrating
memories, spatial navigation.
•
high density of estrogen
receptors.
•
alterations in dendritic spines
associated with estrous cycle.
Ambient Hormone Effects
Qiu L et al, NeuroImage, 2013
Ambient Hormone Effects
Qiu L et al, NeuroImage, 2013
Radial Arm Maze—Spatial Learning and Memory
Corre C et al, Brain Structure & Function, 2014
Only Gonadal Sex Influences RAM Results
Sex chromosomes
Proportion correct visits
Gonadal sex
1
2
3
Day
4
5
1
n=12-13
2
3
Day
Corre C et al, Brain Structure & Function, 2014
4
5
Sex Effects in RAM are Organizational
Corre C et al, Unpublished
How Can Genetics and Animals Help Us?
1. Sex steroid effects
Sex Steroids
Themselves
2. Sex chromosomes
Organizational
effects
Ambient/
Activational
effects
Epigenetics & Sex Differences in the Brain
2015
Mechanisms of Sex-specificity
Cousminer, Widen, and Palmert, Curr Opinion in Endo, Diabetes and Obesity, 2016
Gears
Changing
15, 168 women; 5995 cases of T2DM
Two Models--Investigation of Sex-specificity
• Brain structure and function, where differences matter due to
differences in mental health outcomes
– M:F ratios for depression (1:3), autism (4:1), ADHD (3:1) Alzheimer disease (1:2)
– Males with higher rates of externalizing disorders with pre-pubertal onset; Females with
higher rates of internalizing disorders with post-pubertal onset.
• The timing of puberty, where differences matter due to clinical
presentations and associations with later life outcomes
– Girls tend to develop earlier and are more likely to have precocious puberty
– Boys tend to develop at later ages and are more likely to have delayed puberty
Variation in Timing of Female Pubertal Development. From Tanner, J.M.
Variation in Timing of Male Pubertal Development. From Tanner, J.M.
Precocious
Puberty
Delayed
Puberty
The Timing of Puberty Matters
Fundamental Human Biology
Disorders of Puberty are Common in Clinic
Timing affects health outcomes
Early puberty increases risk of:
--Cardiovascular Disease
--Diabetes
--Breast Cancer
--Testicular cancer
--All cause mortality
Late puberty associates with:
--Decreased risk of ischemic
heart disease
--Increased risk of osteoporosis
Some effects mediated by BMI but this does NOT explain all associations
Underlying Biology Affects Timing and Health
15, 168 women; 5995 cases of T2DM
Elks C et al; Diabetes Care 2013
Underlying Biology Affects Timing and Health
15, 168 women; 5995 cases of T2DM
Questions
(At least) three questions then arise related to our discussion
today
1. When moving from general (brain structure and function) to
specific (timing of puberty), is there evidence that the same
mechanisms are in play?
2. Can genetic investigation identify factors that modulate the
timing of puberty and provide clues to the mechanisms of
male-female differences?
3. Can we learn anything about the links between pubertal
timing and health outcomes?
How Can Genetic Approaches Help Us?
1.
Findings from 4CG mice
Females
100
80
60
40
XX F (n=40)
XY F (n=35)
20
0
26
28
30
32
34
36
% Animals with PS
% Animals with VO
Sexual maturation occurs
at the same rate in XX and XY 4CG mice
Males
100
80
60
40
XY M (n=45)
XX M (n=48)
20
0
26
28
pnd
Corre C et al, Brain Structure & Function, 2014
30
pnd
32
34
36
How Can Genetic Approaches Help Us?
1.
2.
Findings from 4CG mice
Findings from GWAS
GWAS and the X Chromosome
rs 762080, near IGFS1
rs 5914101, near FAAH2
Sex-Specific GWAS Findings--Not X related
Day FR et al, Nature Communications, 2015
Evidence of Sex-Specificity—Broad Phenotypes
Cousminer, Widen, and Palmert, Curr Opinion in Endo, Diabetes and Obesity, 2016
How Can Genetic Approaches Help Us?
1.
2.
Findings from 4CG mice
Findings from GWAS
Specific Loci
GWAS and Menarche
On line, May 17, 2009
LIN28B and Menarche
Perry JR et al, Nature 2014
Lin28 pathway regulates the HPG axis
On line, May 30, 2010
LIN28A/B—What do they do?
MicroRNAs are small, ~22 nucleotide, non-coding RNAs that are
processed from ~200 nucleotide precursors. miRNAs repress
target mRNAs through an antisense mechanism.
LIN28A/B—What does they do?
LIN28 inhibitors miRNA processing; inhibit production of let-7 miRNAs.
Lin28 pathway regulates the HPG axis
• What happens when we modulate individual components of the pathway?
• Are any sex specific effects observed?
Effects of Lin28a Modulation:
On Puberty
Corre C et al, J of Endocrinology, 2016
Effects of Lin28b Modulation:
On Puberty
Corre C et al, J of Endocrinology, 2016
Effects of let-7 Modulation:
On Puberty
Corre C et al, J of Endocrinology, 2016
Lin28 pathway regulates the HPG axis
• What happens when we modulate individual components of the pathway?
• Lin28b LOF & let-7 GOF have consistent effects
• Lin28a has different effects on pubertal timing than Lin28b and let-7
• Are any sex specific effects observed?
• Yes! Lin28b and let-7 exert male specific effects on puberty
• Pubertal timing may, at least in part, be let-7 independent in female
and let-7 dependent in male mice.
Lin28 pathway regulates the HPG axis
• What happens when we modulate individual components of the pathway?
• Lin28b LOF & let-7 GOF have consistent effects
• Lin28a has different effects on pubertal timing than Lin28b and let-7
• Are any sex specific effects observed?
• Yes! Lin28b and let-7 exert male specific effects on puberty
• Pubertal timing may, at least in part, be let-7 independent in female
and let-7 dependent in male mice.
True in humans too? We don’t know
What is known about Lin28/let-7 axis & puberty:
Revised
1.
Lin28a and Lin28b have different effects on male and female
mice.
2.
Pubertal timing may, at least in part, be let-7 independent in
female and let-7 dependent in male mice.
3.
True in humans too? We don’t know.
But important if so—
Would be one of few mechanisms to regulate the HPG axis
in a sex-specific manner.
And we know timing of puberty varies among boys and
girls….
Lin28 Pathway also Plays Important Roles in
Carcinogenesis and Regulation of Metabolism
Pathway may link regulation of pubertal timing to associated health outcomes
How Can Genetics Help Us?
1.
2.
Findings from 4CG mice
Findings from GWAS
Specific Loci
3.
Findings from epigenetic studies
Perturb and test role of epigenetics
Perturbation
SAHA
L-methionine
Control
HDACi
methyl donor
25mg/kg
1g/kg
water or
vehicle
 histone acetylation
 DNA methylation
DNA methylation
 Gene expression
 Gene expression
No change
Perturbation changes pubertal timing
Rzeczkowska P et al, Neuroendocrinology, 2014
Summary of epigenetic perturbations
and effects on puberty
Epigenetic mechanism
Perturbation
Mechanism of
action
Consequence to
transcription
Effect on pubertal
timing
Interpretation of
mechanism
AZA
SAHA
L-MET
DNA
methylation
Histone
Acetylation
DNA
methylation
Allow gene expression
Inhibit gene
expression
Delayed puberty
Earlier puberty
Initiation of puberty requires repression of repressors 
lifting of inhibition
AZA data derive from Lomniczi et al,
SAHA and L-MET data derive from Rzeczkowska et al
Next—need to study male vs female effects!
Adapted from
Rzeczkowska et al, Neuroendocrinol 2014
How Can Genetics Help Us?
1.
2.
Findings from 4CG mice
Findings from GWAS
Specific Loci
3.
Findings from epigenetic studies
4.
Findings from expression studies
Which Genes to Study? GWAS Loci to start
153
Genes
Which Genes to Study? “Single gene” disorders
24 Genes
Which ages should we study?
Changes in Expression Occur Before Puberty
Some patterns are not sex specific
Some patterns are not sex specific, but others are
Some patterns are not sex specific, but others are
The Pituitary: Home of Most Sex Specific Patterns?
Questions
(At least) three questions then arise related to our discussion
this morning
1. When moving from general (brain structure and function) to
specific (timing of puberty), is there evidence that the same
mechanisms are in play? Yes!
2. Can genetic investigation identify factors that modulate the
timing of puberty and provide clues to the mechanisms of
male-female differences? Yes!
3. Can we learn anything about the links between pubertal
timing and health outcomes? Yes!
15, 168 women; 5995 cases of T2DM
All explained by sex steroids and sex chromosomes and epigenetics??
Probably not……but some differences certainly are
Acknowledgements
Palmert and Lerch Collaborative Team:
Current:
Jason Lerch
Christina Corre
Shoshana Spring
Dulcie Vousden
Lily Qiu
Other Investigators:
Jane Foster
Past:
Miriam Friedel
Ariane Metcalf
Christian Bellissimo
Garrett Bullivant
Acknowledgements
Palmert, Wilson and Goldenberg Collaborative Team:
Current:
Past:
Mike Wilson
Anna Goldenberg
Christina Corre
Huayun Hou
Liis Uusküla-Reimand
Garrett Bullivant
Ariane Metcalf
Christian Bellissimo
Maisam Makarem