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The Role of Mechanobiology
in Meniscus Tissue
Regeneration and Repair
Amy L. McNulty, PhD
Assistant Professor
Depts. of Orthopaedic Surgery and Pathology
Duke University Medical Center
Meniscus Tissue Function
and Maintenance • Critical biomechanical role in the knee,
providing load support, joint stability,
and congruity
• Maintained through a balance of the
anabolic and catabolic activities of
meniscal cells
• Meniscus cell activity is controlled not
only by biochemical factors in the joint
but also by physical factors associated
with joint loading
Collier & Ghosh, 1995; McNulty et al, 2013; Pangborn & Athanasiou, 2005; Riera et al, 2011
Image adapted from
Sanchez-Adams et al, 2013
Mechanobiology in the Meniscus
• Mechanobiology is the influence of mechanical
factors on the biological response of meniscal
cells
• Experiments across various culture systems
have revealed that the biological response of
meniscal cells is directly influenced by physical
factors
• These studies have revealed new insights into
the mechanotransduction mechanisms involved
in converting physical signals into metabolic
and pro/anti-inflammatory responses
M
Physiologic Loading: Exercise: Δ Tissue composition Loading following immobilization: ↓ Matrix degradation ↑ Anti-inflammatory cytokines
Dynamic compression (~10%): ↑ Anabolism, ↓ IL-1 effects Cyclic hydrostatic pressure: ↑ Anabolic genes ↓ Catabolic & inflammatory genes
Pathologic Loading: Immobilization: ↓ Tissue composition and function Impact: ↓ Cell viability ↑ Pro-inflammatory mediators
Dynamic compression (>20%): ↑ Catabolism & inflammation Injurious strains (<40%): ↑ Cell death, ↓ metabolism ↑ Cell lysis
Cyclic tensile strain: ↓ IL-1 and TNF-a effects Δ NF-κB pathway to modulate inflammatory response
Effects of Loading on the Meniscus
Figure from McNulty & Guilak, 2015
Mikic et al, 2000; Klein et al, 1982; Videman et al, 1979; Djurasovic et al, 1998; Anderson et al, 1993; Ochi et al, 1997; Killian
et al, 2014; McHenry et al, 2006; Gupta et al, 2008; Zielinska et al, 2009; Suzuki et al, 2006; Natsu-Ume et al, 2005; Agarwal
et al, 2001; Ferretti et al, 2006; Nishimuta & Levenston, 2012; Kisiday et al, 2010
From Deschner et al, 2006
Role of Mechanical Loading in
Tissue Engineering
• Understanding of mechanobiology can be
exploited to promote meniscal regeneration and
repair
• Tissue engineering strategies are being utilized to
generate new meniscal tissue (AufderHeide & Athanasiou,
2004; Guilak et al., 2014)
Cells
Scaffolds
Mechanical
Stimulation
Growth
factors
Guilak et al., 2001
Duration of Dynamic Compression Modulates
ECM Production and Mechanical Properties
• Immature bovine meniscal fibrochondrocytes in
alginate were cast into a meniscus shaped mold
• Dynamic compressive loading of anatomically
shaped scaffolds—15% strain, 1 Hz, 3x/week
– 2 weeks ECM content enhanced and compressive
modulus increased but reduced by 6 weeks (Ballyns &
Bonassar, 2011)
– 2 weeks of loading followed by static culture increased
collagen bundle formation, sGAG content, and
mechanical properties (Puetzer et al., 2012)
From Puetzer et al., 2012
From Nathan et al., 2011
Scaffold Organization and Mechanical
Loading Drives the Orientation of Cells
Non-aligned Aligned
Non-aligned Aligned Aligned
+ 5% Strain Aligned
+ 10% Strain Green = F actin
Blue = DNA
Electrospun PCL scaffolds and meniscus fibrochondrocytes
From Baker et al., 2011
Scaffold Organization and Mechanical
Loading Improves the Functional Properties
of Tissue Engineered Meniscus Constructs
Aligned PCL scaffolds + MSCs
6% tensile strain, 1 Hz
Physiologic Loading of Meniscal Constructs
Induces Local Changes in Tissue
Organization and Mechanical Properties
From Puetzer & Bonassar, 2016
• Immature bovine fibrochondrocytes in type I collagen gels
• 5 & 10% dynamic strain 2x/day, 3x/week, 1Hz
• 2 – 4 weeks in culture
Green = collagen
Red = cells
10%
Str
ain
5%
Str
ain
Conclusions: Tissue Regeneration
• These studies have shown that, with mechanical
stimulation, it is possible to mimic the structure
and biomechanical environment of the meniscus
to begin approaching functional properties for
tissue engineered menisci
• Further optimization is still required to establish
the optimal loading parameters and scaffold
design to recapitulate the mechanical properties
of the meniscus and the appropriate
extracellular matrix structure and composition
for tissue regeneration
Inflammatory Cytokines in the Joint
• Increased levels of inflammatory cytokines are
observed in injured and degenerate joints
• Synovial fluid concentrations:
– Meniscus Tear: 25–175 pg/mL IL-1α (Vangsness, Jr. et al., 2006)
– Mild OA: 43 pg/mL IL-1α (McNulty et al., 2013)
– Moderate OA: 287 pg/mL IL-1α (McNulty et al., 2013)
• IL-1 suppresses matrix biosynthesis and
increases enzymatic degradation in joint tissues
• Can we use the mecho-responsiveness of
meniscus cells to promote repair in the
inflammatory environment of an injured joint?
IL-1 Decreases Interfacial Shear Strength
a p < 0.05 compared to all other conditions, except 10 pg/mL b p < 0.001 compared to all other conditions, except day 42 control c p < 0.05 compared to 100 pg/mL and 1000 pg/mL treatments d p < 0.001 compared to all other conditions, except day 28 control
0
5
10
15
20
25
Sh
ea
r S
tre
ng
th (
kP
a)
IL-1 (pg/mL) 0 0 10 100 1000 0 10 100 1000 0 10 100 1000
b
d
a c
Day 0 Day 14 Day 28 Day 42
McNulty et al, 2007
Meniscal Repair Model System • Explants
– 5 mm outer ring/3 mm inner core
– Average 2.4 mm thick
• IL-1 stimulation
– 100pg/mL
• Dynamic Compression
– Peak to peak strain:
• 1% , 10%, and 26%
– 1 Hz sinusoidal waveform
– 4 hours/day, 14 days
• Outcome measures: – MMP Activity
– S-GAG Release
– NO Production
– Interfacial Shear Strength
MMP Activity is Decreased by Loading in the
Presence of IL-1
0
1000
2000
3000
4000
5000
FU
/mg
F
U/m
g
1% Strain
0
1000
2000
3000
4000
5000 10% Strain
0
1000
2000
3000
4000
5000
FU
/mg
No Strain Strain No Strain
+ IL-1
Strain
+ IL-1
a
a
a 26% Strain
a: p < 0.03 compard to all other treatments McNulty et al, 2010
S-GAG Release is Decreased by Loading in
the Presence of IL-1
0
10
20
30
40
50
60
70
80
µg
S-G
AG
/mg
1% Strain
10% Strain
26% Strain
0
10
20
30
40
50
60
70
80
µg
S-G
AG
/mg
0
10
20
30
40
50
60
70
80
µg
S-G
AG
/mg
No Strain Strain No Strain +
IL-1
Strain +
IL-1
a
a
b
a
b
a: p < 0.005 compared to all other treatments.
b: p < 0.009 compared to no strain and strain. McNulty et al, 2010
NO Release is Blocked by Loading in the
Presence of IL-1 1% Strain
10% Strain
26% Strain
0
5
10
15
µm
ol
NO
x/g
0
5
10
15
µm
ol
NO
x/g
µ
mo
l N
Ox
/g
0
5
10
15
No Strain Strain No Strain
+ IL-1
Strain
+ IL-1
a
a
a
a
a
a: p < 0.002 compared to all other treatments McNulty et al, 2010
Loading Increased the Shear Strength of
Repair in the Presence of IL-1
0
2
4
6
8
10
12
14
16
No Strain Strain No Strain
+ IL-1
Strain
+ IL-1
0
2
4
6
8
10
12
14
16
kP
a
1% Strain
10% Strain
26% Strain b
a
a
c
0
2
4
6
8
10
12
14
16
kP
a
kP
a
a: p = 0.03 compared to all other treatments
b: p < 0.005 compared to no strain and no strain + IL-1
c: p = 0.006 compared to strain + IL-1 McNulty et al, 2010
Mechanical Loading Enhances
Meniscus Repair
• Dynamic compression antagonized the IL-1 mediated effects that inhibited meniscal repair
• At 26% strain meniscal healing was enhanced
• The mechanism(s) by which loading antagonizes the effects of IL-1 need to be investigated further – Decrease in the IL-1 type I receptor and/or increase in the type II
decoy receptor (Attur et al., 2000; Chowdhury et al., 2008)
– Upregulation of IL-1 receptor antagonist, which is able to block decreases in cartilage proteoglycan synthesis caused by static compression (Murata et al., 2003)
– May regulate IL-1 signaling mediators that are downstream of the IL-1 receptor, such as NF-kB, RANK, and RANK ligand (Deschner et al., 2006)
– May alter the expression of other pro-inflammatory mediators, such as TNF (Ferretti et al., 2006)
– May alter the expression and/or activity of mechanosensitive channels
Conclusions: Tissue Repair
• Joint loading through physical therapy
following a meniscal tear may be beneficial to
promote integrative tissue repair
• More extensive understanding of
mechanobiologic responses in the meniscus
will hopefully lead to the development of new
physical and/or pharmacologic therapies to
enhance repair
Conclusion
More work is still needed to establish a
thorough understanding of the
mechanobiology of the meniscus under
physiologic and pathologic loading
conditions that can provide important
insights into the prevention and treatment
of meniscal injuries and degeneration.
Acknowledgements McNulty Lab: Current:
Dawn Chasse
Noelani Ho
James Nishimuta
Jennifer Stencel
Past:
Katherine Riera
Nicole Rothfusz
Jacob Ruprecht
Tyler Waanders
Rebecca Wilusz
Collaborators: Farshid Guilak, Washington University
J. Brice Weinberg, VA Medical Center
Funding Sources:
NIH
VA Rehabilitation Research Service Award
