For OCT-embedded tissue sections, the
OCT compound was removed by rinsing with PBS for 5 min after tissue
slides were warmed to room temperature. For FFPE tissue sections,
paraffin was removed by rinsing with xylene, 100% ethanol, 95% ethanol,
50% ethanol, and deionized water for two 5 min cycles of each solvent
in consecutive order. The deparaffinized tissue was directly used
for staining without any antigen-retrieval process. After the embedding
material was removed, 5% goat serum in PBS was added to the tissue
sections and incubated for 20 min at room temperature to block nonspecific
binding. For B-CHP staining, any endogenous biotin in the tissue was
blocked using the endogenous biotin-blocking kit following the manufacturer’s
protocol after the serum blocking step. Because CHP can self-assemble
into homotrimers in solution over time (e.g., during storage at 4 °C) and lose its driving force
for collagen hybridization, the trimeric CHP was thermally dissociated
to single strands by heating briefly at 80 °C before it was used
to bind unfolded collagen.25 (link) To prevent
undesired thermal denaturation of the tissue, the 80 °C CHP solution
was quenched quickly to room temperature immediately prior to addition
to tissue samples (dead time <2 min). The CHP trimerization has
a third-order folding rate with a half-time on the order of hours
at low μM concentrations.26 ,65 (link),66 (link) Therefore, the heating and quenching protocol used here (Figure S1 ) ensures that CHP strands predominate
in the active monomer form until exposed to denatured collagen. After
the blocking solutions were gently removed from the slides, heat-activated
solutions of single-strand CHPs were added to the tissue sections
in the following fashion. CHP solution (15 μM of B-CHP or F-CHP,
50–200 μL per section) in PBS or PBS containing 1% BSA
(when costaining with an antibody) was heated for 5 min in an 80 °C
water bath to dissociate the trimeric peptides, followed by immediate
incubation in an ice/water bath (for 15–90 s depending on the
solution volume) to quench the hot solution to room temperature. When
needed, an antibody was diluted into this quenched CHP solution for
costaining. The solution containing the quenched CHP monomers was
quickly pipetted to each slide (usually 50–200 μL per
section) within 1 min. The tissue samples were incubated in a humidity
chamber at 4 °C overnight. After staining, the slides were incubated
for 5 min in 100 mL of PBS at room temperature to remove the unbound
material and the washing step was repeated three times. For B-CHP
staining, the tissue sections were subsequently incubated with AlexaFluor647-labeled
streptavidin (0.005 mg/mL) in a PBS solution containing 1% BSA. To
detect the costained primary antibody, a labeled secondary antibody
was either diluted into the AlexaFluor647-streptavidin solution (for
B-CHP costaining) or added to the slides directly after dilution in
a PBS solution containing 1% BSA (for F-CHP costaining). The tissues
were incubated with the streptavidin and/or secondary antibody solution
in a humidity chamber for 1 h at room temperature. Where indicated,
cell nuclei were stained with Hoechst 33342 in PBS for 20 min according
to the manufacturer’s recommendation. Finally, the tissue sections
were rinsed with PBS three times and mounted with Fluoroshield. The
specific CHP, antibody types, and concentrations used in each experiment
are presented inTable S1 . All histological
staining experiments were performed on at least three different sections
from each tissue sample. For the myocardial infarction, glomerulonephritis,
lung fibrosis, and skin aging experiments, tissue samples from three
animals within each experimental group (e.g., the normal control group, the week 3 group) were analyzed.
OCT compound was removed by rinsing with PBS for 5 min after tissue
slides were warmed to room temperature. For FFPE tissue sections,
paraffin was removed by rinsing with xylene, 100% ethanol, 95% ethanol,
50% ethanol, and deionized water for two 5 min cycles of each solvent
in consecutive order. The deparaffinized tissue was directly used
for staining without any antigen-retrieval process. After the embedding
material was removed, 5% goat serum in PBS was added to the tissue
sections and incubated for 20 min at room temperature to block nonspecific
binding. For B-CHP staining, any endogenous biotin in the tissue was
blocked using the endogenous biotin-blocking kit following the manufacturer’s
protocol after the serum blocking step. Because CHP can self-assemble
into homotrimers in solution over time (e.g., during storage at 4 °C) and lose its driving force
for collagen hybridization, the trimeric CHP was thermally dissociated
to single strands by heating briefly at 80 °C before it was used
to bind unfolded collagen.25 (link) To prevent
undesired thermal denaturation of the tissue, the 80 °C CHP solution
was quenched quickly to room temperature immediately prior to addition
to tissue samples (dead time <2 min). The CHP trimerization has
a third-order folding rate with a half-time on the order of hours
at low μM concentrations.26 ,65 (link),66 (link) Therefore, the heating and quenching protocol used here (
in the active monomer form until exposed to denatured collagen. After
the blocking solutions were gently removed from the slides, heat-activated
solutions of single-strand CHPs were added to the tissue sections
in the following fashion. CHP solution (15 μM of B-CHP or F-CHP,
50–200 μL per section) in PBS or PBS containing 1% BSA
(when costaining with an antibody) was heated for 5 min in an 80 °C
water bath to dissociate the trimeric peptides, followed by immediate
incubation in an ice/water bath (for 15–90 s depending on the
solution volume) to quench the hot solution to room temperature. When
needed, an antibody was diluted into this quenched CHP solution for
costaining. The solution containing the quenched CHP monomers was
quickly pipetted to each slide (usually 50–200 μL per
section) within 1 min. The tissue samples were incubated in a humidity
chamber at 4 °C overnight. After staining, the slides were incubated
for 5 min in 100 mL of PBS at room temperature to remove the unbound
material and the washing step was repeated three times. For B-CHP
staining, the tissue sections were subsequently incubated with AlexaFluor647-labeled
streptavidin (0.005 mg/mL) in a PBS solution containing 1% BSA. To
detect the costained primary antibody, a labeled secondary antibody
was either diluted into the AlexaFluor647-streptavidin solution (for
B-CHP costaining) or added to the slides directly after dilution in
a PBS solution containing 1% BSA (for F-CHP costaining). The tissues
were incubated with the streptavidin and/or secondary antibody solution
in a humidity chamber for 1 h at room temperature. Where indicated,
cell nuclei were stained with Hoechst 33342 in PBS for 20 min according
to the manufacturer’s recommendation. Finally, the tissue sections
were rinsed with PBS three times and mounted with Fluoroshield. The
specific CHP, antibody types, and concentrations used in each experiment
are presented in
staining experiments were performed on at least three different sections
from each tissue sample. For the myocardial infarction, glomerulonephritis,
lung fibrosis, and skin aging experiments, tissue samples from three
animals within each experimental group (e.g., the normal control group, the week 3 group) were analyzed.