The Journal of Neuroscience, September 1, 2002, 22(17):7493–7501
Dynamic Pattern of Reg-2 Expression in Rat Sensory Neurons after
Peripheral Nerve Injury
Sharon Averill,1* Danny R. Davis,2* Peter J. Shortland,1 John V. Priestley,1 and Stephen P. Hunt2
Department of Neuroscience, Queen Mary University of London, London, E1 4NS, United Kingdom, and 2Department of
Anatomy and Developmental Biology, University College London, London, WC1E 6BT, United Kingdom
1
The 16 kDa pancreatitis-associated protein Reg-2 has recently
been shown to facilitate the regeneration of motor and sensory
neurons after peripheral nerve injury in the adult rat. Reg-2 has
also been shown to be a neurotrophic factor that is an essential
intermediate in the pathways through which CNTF supports the
survival of motor neurons during development. Here we report
the dynamic expression of Reg-2 in rat sensory neurons after
peripheral nerve injury. Reg-2 is normally not expressed by
dorsal root ganglion (DRG) cells, but we show, using immunocytochemistry, that Reg-2 is rapidly upregulated in DRG cells
after sciatic nerve transection and after 24 hr recovery is expressed almost exclusively in small-diameter neurons that bind
the lectin Griffonia simplicifolia IB4 and express the purinoceptor P2X3. However, by 7 d after axotomy, Reg-2 is expressed in
medium to large neurons and coexists partly with the neu-
ropeptides galanin and neuropeptide Y, which are also upregulated after peripheral nerve transection. At this time point,
Reg-2 is no longer expressed in small neurons, and there is no
colocalization with IB4 binding neurons, demonstrating a shift
in Reg-2 expression from one subset of DRG neurons to another. We also show by double labeling for activating transcription factor 3, a transcription factor that is upregulated after
nerve injury, that Reg-2 expression occurs predominantly in
axotomized DRG cells but that a small percentage of uninjured
DRG cells also upregulate Reg-2. The selective expression
within IB4/P2X3 cells, and the dynamic shift from small to large
cells, is unique among DRG peptides and suggests that Reg-2
has a distinctive role in the injury response.
Key words: regeneration; axotomy; dorsal root ganglia; neuropeptide; peripheral nerve injury; Reg-2
Reg-2 (also known as PAP1 in rat, RegIII in mouse, and
HIP/PAP in humans) is a 16 kDa secretory protein that has
recently been shown to have proregenerative properties in motor
and sensory neurons after peripheral nerve injury in the rat
(Livesey et al., 1997). Reg-2 is massively upregulated in subsets of
sensory neurons and in all regenerating ␣ motor neurons after
sciatic nerve injury (Livesey et al., 1997). In vitro, Reg-2 has a
mitogenic effect on Schwann cells, and direct injection of Reg-2
antibody into the crushed nerve retarded the regeneration of the
relevant subsets of sensory and motor neurons. These results
strongly imply a novel principle: neurons do not simply grow
passively through a permissive environment, but they can actively
secrete factors that can change the environment through which
they are regenerating. Reg-2 is also constitutively expressed in
subpopulations of motor neurons during development, and this
expression is driven by cytokines of the interleukin-6 (IL-6)
family, which includes ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and cardiotrophin (CT-1) (Livesey
et al., 1997). These cytokines have been shown to prevent motor
neuron cell death that follows neonatal axotomy (Sendtner et al.,
1990; Cheema et al., 1994; Pennica et al., 1996) and to prolong
motor neuron survival in strains of mice that show spontaneous
motor neuron cell death (Sendtner et al., 1992; Mitsumoto et al.,
1994; Lindsay, 1996; Winter et al., 1996; Bordet et al., 1999).
More recently, Nishimune and colleagues (2000) have shown that
during development Reg-2 is a neurotrophic factor that is an
essential intermediate in the pathways through which CNTF
supports the survival of motor neurons (Nishimune et al., 2000).
The role of Reg-2 expression in sensory neurons of the dorsal
root ganglion (DRG) has yet to be elucidated but is clearly of
interest because peripheral sensory neurons have the capacity to
regenerate, and neuropoietic cytokines play a role in the maintenance of sensory neurons after peripheral nerve injury (Simon
et al., 1995; Thompson et al., 1998; Thier et al., 1999). In a
previous study (Livesey et al., 1997) Reg-2 was shown to be
upregulated in a subpopulation of DRG cells after sciatic nerve
crush, but the DRG cell type was not characterized. Here we have
performed a detailed analysis of Reg-2 expression in lumbar
DRG cells and their central projections at various time points
after sciatic nerve crush and transection. Reg-2 expression is
dynamic, appearing within distinct populations of sensory neurons at different times after axon damage.
Received July 26, 2001; revised April 29, 2002; accepted May 3, 2002.
We gratefully acknowledge support from the European Commission (S.P.H.) and
the Wellcome Trust (J.V.P.).
*S.A. and D.R.D. contributed equally to this study.
Correspondence should be addressed to Prof. John Priestley, Department of
Neuroscience, Queen Mary University of London, Mile End Road, London, E1
4NS, United Kingdom. E-mail: j.v.priestley@qmul.ac.uk.
Copyright © 2002 Society for Neuroscience 0270-6474/02/227493-09$15.00/0
MATERIALS AND METHODS
Materials and antibodies. All chemicals and materials were obtained from
Sigma-Aldrich (Poole, UK) or Merck-BDH (Lutterworth, UK) unless
stated otherwise. In this study, the following primary antibodies were used:
anti-Reg-2 polyclonal antibody (Livesey et al., 1997) was raised in rabbit
against whole recombinant protein and used in these studies at 1:20,000 for
immunoperoxidase, 1:8,000 for indirect labeled immunofluorescence, and
1:120,000 with tyramide signal amplification (TSA; see below). Anti-trkA
rabbit polyclonal antibody (Upstate Biotechnology, Lake Placid, NY) was
used at 1:10,000 (TSA procedure); rabbit anti-neuropeptide Y (NPY) and
anti-galanin antisera (both Affiniti, Exeter, UK) were used at 1:2,000, and
guinea pig anti-P2X3 antiserum (Neuromics, Minneapolis, MN) was used
at 1:1,500,000 (TSA procedure). Anti-activating transcription factor 3
(ATF3) rabbit polyclonal antibody (Santa Cruz, CA) was used at 1:200.
Isolectin Griffonia simplicifolia IB4 FITC conjugate (Sigma-Aldrich, Dorset, UK) was used at a dilution of 1:1000.
Averill et al. • Reg-2 in Injured Sensory Neurons
7494 J. Neurosci., September 1, 2002, 22(17):7493–7501
Table 1. The percentage of DRG cells that express Reg-2, IB4, trkA, galanin (GAL), or ATF3 immunoreactivities at various time points after sciatic
nerve transection
Time point
Reg-2
IB4
trkA
GAL
ATF3
Control
24 hr
7d
30 d
0.8 ⫾ 0.4
14.1 ⫾ 1.0
10.0 ⫾ 1.5 (4)
10.9 ⫾ 0.5
49.7 ⫾ 2.0
44.3 ⫾ 2.4
35.5 ⫾ 0.4
32.2 ⫾ 5.3
44.0 ⫾ 0.6
47.5 ⫾ 3.2
31.2 ⫾ 0.9
39.0 ⫾ 3.2
8.7 (2)
22.5 (2)
40.4 ⫾ 3.2
39.3 ⫾ 7.4
0.8 ⫾ 0.4
72.9 ⫾ 4.4 (5)
58.7 ⫾ 6.6
67.0 ⫾ 5.0
The numbers shown are mean ⫾ SEM and are based on counts from three animals unless indicated otherwise.
Animals and surger y. For all experiments, male Sprague Dawley or
Wistar rats of ⬃150 –200 gm were used, and preliminary experiments
revealed no difference in Reg-2 expression, or upregulation, between
these two strains. Unilateral sciatic nerve crush (15 Wistar, 4 Sprague
Dawley) or transection (12 Wistar, 16 Sprague Dawley) was performed at
mid-thigh level under deep anesthesia [4% (v/ v) halothane for induction
and maintained with 2% (v/ v) during surgery]. For transection the sciatic
nerve was first ligated and then cut distal to the ligature. Animals were
allowed to recover for 24 hr, 5 d, 7 d, 30 d, or 8 weeks, at which time tissue
Figure 1. Expression of Reg-2 in DRG
after peripheral nerve injury. A–D show
Reg-2 immunoreactivity in ipsilateral
(A–C) and naı̈ve control ( D) lumbar
DRG 1 d ( A), 7 d ( B), and 30 d ( C)
after sciatic nerve transection. Reg-2 is
upregulated after sciatic transection,
but expression is dynamic, appearing
predominantly in small cells at 1 d ( A)
but in medium and large cells at 7 d ( B).
E–H show the disposition of Reg-2immunoreactive axons in an L4 ganglion (DRG) with attached ventral root
(VR), dorsal root (DR), and spinal
nerve (SN ) at 1 d after sciatic transection. The labeling in E shows the areas
that were sampled for the highmagnification images in F–H. Immunoreactive axons (arrows) can be observed
within and on the peripheral side of the
ganglion ( F) as well as within the spinal
nerve ( G). However, very few axons
were present on the central side of the
ganglion or within the attached dorsal
root ( H ) or ventral root. Scale bars:
A–D, 100 m ; E, 200 m; F–H, 50 m.
was removed for immunocytochemical analysis. In some experiments
(n ⫽ 4), the sciatic nerve was injected with 5 l of 5% (w/ v) Fast Blue at
the time of transection to retrogradely label the axtomized sciatic afferents. In six other animals, axonal transport was studied by ligating the
L4/ L5 lumbar dorsal roots and proximal portion of sciatic nerve (two
animals) or by ligating the sciatic nerve (two animals) or saphenous nerve
(two animals) at mid-thigh level 3 d before perf usion fixation.
Tissue processing. Rats were deeply anesthetized with pentobarbitone (60
mg/kg, i.p.) and transcardially perfused with ⬃100 ml sterile saline con-
Averill et al. • Reg-2 in Injured Sensory Neurons
Figure 2. Size distribution of Reg-2-immunoreactive sensory neurons in
L4/5 DRG after sciatic nerve transection. Note that at 24 hr many
small-diameter sensory neurons are immunoreactive, but by 5 d predominantly medium-diameter cells show Reg-2 expression. At 5 d after transection, some neurons are large, as indicated by the long tail seen on the
size distribution graph, which is not seen by 8 weeks after transection.
taining 5000 U/l heparin followed by ⬃300 ml of either 4% (w/v) paraformaldehyde in 0.1 M phosphate buffer, pH 7.4 (PB), or PLP fixative composed of 2% (w/v) paraformaldehyde, 100 M sodium metaperiodate, and
750 M L-lysine monhydrochloride in PB. Both ipsilateral and contralateral
L4 and L5 lumbar DRGs, lumbar spinal cord, and lower medulla were
dissected and postfixed for 2 hr at 4°C and then transferred to 20 –30%
(w/v) sucrose in 0.1 M PB containing 0.02% (w/v) sodium azide. Tissue was
J. Neurosci., September 1, 2002, 22(17):7493–7501 7495
frozen on dry ice, and sectioning was performed on either a freezing
microtome (Leica, Hemel Hempstead, UK) or a cryostat (Leica).
Microtome sections were cut at 20 or 40 m into 5% (w/ v) sucrose in
0.1 M PB containing 0.02% (w/ v) sodium azide and were processed for
Reg-2 immunoreactivity as free-floating sections. Tissue for cryostat
sectioning was embedded in OC T, cut at 6 m, and thaw-mounted onto
Superfrost plus microscope slides.
Immunocytochemistry. To determine localization of expression in the
DRG for cell size distribution analysis, free-floating microtome sections
were first rinsed in 0.1 M PB, followed by a 30 min incubation in 0.1 M PB
containing 0.6% (w/v) hydrogen peroxide at room temperature to block any
endogenous peroxidase activity. Sections were then transferred into 0.1 M
PB containing 3% (v/v) normal goat serum, 0.25% (v/v) Triton X-100, and
0.02% (w/v) sodium azide (PBT) and incubated for 1 hr at room temperature. For incubation in primary antibody, sections were transferred into
fresh PBT containing Reg-2 polyclonal antiserum and incubated at 4°C for
2 d. After washes in 0.1 M PB, sections were incubated in biotinylated goat
anti-rabbit IgG (Vector Laboratories, Peterborough, UK; 1:400 in PBT) for
1 hr at room temperature. After further washes, sections were incubated in
avidin–biotin complex (Vector Laboratories; 1:200 in 0.1 M PB) that had
been premixed 30 min previously. Finally, sections were washed again in 0.1
M PB followed by a brief wash in 0.15 M Tris-HCl, pH 7.4. Sections were
then transferred into 0.15 M Tris-HCl, pH 7.4, containing 0.25 mg/ml
diaminobenzidine, 2 mg/ml nickel sulfate, and 0.003% (w/v) hydrogen
peroxide to induce color reaction. Tissue sections were washed in 0.1 M PB
to stop the color development. Mounted sections were allowed to air-dry
overnight. They were then dehydrated through increasing alcohol concentrations and placed in Histoclear. Slides were then coverslipped using DPX
as mountant.
For double-labeling experiments, standard immunofluorescence procedures were used using either indirect labeled immunofluorescence or a
TSA kit (N EN Life Science Products, Hounslow, UK (Averill et al., 1995;
Michael et al., 1997). Incubations were performed at room temperature
and consisted of 1 hr in 10% (v/ v) normal serum followed by 18 –36 hr in
each set of primary antisera and 3 hr in the developing secondary
antisera. The two sets of antisera were applied sequentially, and this
normally involved Reg-2 TSA followed by indirect-labeled immunofluo-
Figure 3. Analysis of Reg-2 immunoreactivity in the spinal cord and brain
stem. A–D show the lumbar spinal cord
7 d after sciatic nerve transection. Reg-2
immunoreactivity is expressed in the
ventral horn (VH ) in axotomized motoneurons (A, arrows) but is absent from
the dorsal horn (DH ), indicating that it
is not present in the central terminals of
axotomized primary afferents. B–D
show the superficial dorsal horn at high
magnification, stained for IB4, Reg-2,
or CGRP. Asterisks indicate the central
terminal field of the axotomized sciatic
nerve, which has downregulated IB4
( B). However, Reg-2 immunoreactivity
in this region is not above background
staining ( C), although CGRP staining
confirms that primary afferent terminals
are present ( D). E and F show the dorsal medulla 30 d after sciatic nerve transection. Ipsilateral to the transection,
neuropeptide Y (NPY ) immunoreactivity is upregulated within the gracile nucleus ( E) in the central terminal fields
of the axotomized primary afferents
(asterisk). However, there is no indication of Reg-2 immunoreactivity in that
region ( F). Scale bars: A, 200 m; B–F,
100 m.
Averill et al. • Reg-2 in Injured Sensory Neurons
7496 J. Neurosci., September 1, 2002, 22(17):7493–7501
rescence. Tetramethylrhodamine isothiocyanate (TRI TC)-labeled antirabbit IgG was used for indirect immunofluorescence (Jackson ImmunoResearch, West Grove, PA; 1:400 dilution). TSA labeling was
performed using biotinylated goat anti-rabbit IgG (1:400; Vector Laboratories) and Vectastain Elite peroxidase reagent (Vector Laboratories)
followed by biotinyl tyramide (N EN Life Science Products, Hounslow,
UK ; TSA-indirect kit) and E xtrAvidin-FI TC (1:500, Sigma-Aldrich,
Dorset, UK). After incubation in secondary reagents, sections were
washed briefly in PBS and then mounted in PBS/glycerol (1:3) containing
2.5% (w/ v) 1,4 diazobicyclo (2,2,2) octane (DABC O; anti-fading agent).
Controls for double labeling included reversing the order of the primary
antisera, as well as omitting the first or second primary antiserum.
Image anal ysis. For cell size distribution and fast blue experiments,
images were obtained using a Leica DMR microscope and either a JVC
K Y-F50 color video camera (for DAB-labeled sections) or a Hamamatsu
C5985 CCD camera (for immunofluorescence). Images were grabbed
using VisionE xplorer software, and cell diameters were measured using
Leica Qwin (v2.2) image analysis software. For cell size distribution, we
measured the diameters of Reg-2-positive cells from at least 16 sections
taken from three animals at each time point. Only cells that displayed a
distinct nucleus were measured. For immunofluorescence sections, quantitation of the proportion of Reg-2 expressing DRG cells was determined
by counting the number of immunoreactive and non-immunoreactive
neuronal profiles. In double-labeled sections, the percentage of Reg-2expressing cells expressing a second marker was assessed by switching
between FI TC and TRI TC filter blocks. At least 250 labeled DRG cells
were examined for each marker and counted on randomly chosen sections. Photographs were taken using a Hamamatsu C4742-95 digital
camera, and plates were assembled using Adobe Photoshop.
Figure 4. Axonal transport of Reg-2.
A, C, and E show anterograde accumulation proximal to a L4/L5 dorsal root
ligature, and B, D, and F show anterograde accumulation proximal to a sciatic nerve ligature. Vertical arrows in A
and B indicate the site of each ligature.
CGRP shows a prominent accumulation
in dorsal roots ( A) and in sciatic nerve
( B), whereas very little Reg-2 accumulation (C, D, arrows) is seen in dorsal
roots compared with sciatic nerve. IB4
staining proximal to the ligatures is not
as prominent as CGRP but is present in
both dorsal roots ( E) and sciatic nerve
( F). Scale bars: A, C, E, 100 m; B, D, F,
200 m.
RESULTS
Reg-2 immunoreactivity was assessed in rat lumbar DRG cells at
various times after sciatic nerve injury. By 24 hr after nerve
transection, Reg-2 was expressed by ⬃14% of DRG cells (Table
1). Immunoreactivity was observed in predominantly small diameter (26.46 m ⫾ 4.65) sensory neurons, which appeared evenly
distributed throughout the DRG (Figs. 1A, 2). By 5–7 d after
sciatic nerve section, a similar percentage of DRG cells were
stained, but the immunoreactivity was now observed in predominantly medium to large diameter (44.47 ⫾ 8.98 m) cells with
some cells having very large diameters (⬎60 m) (Figs. 1 B, 2).
Immunoreactivity remained elevated at longer time points, but by
8 weeks the Reg-2-positive cells were predominantly of small to
medium diameter with no very large cells observed (Fig. 2).
Similar results were obtained with both nerve transection and
crush at 1 and 7 d survival. Reg-2 immunoreactivity in contralateral lumbar DRG and in naı̈ve control DRG was observed in just
a few isolated profiles at each time point and omission of primary
antisera resulted in a loss of immunoreactivity (not shown). In
some material, light labeling of satellite glial cells was present (see
Fig. 7C), but controls indicated that this was not specific. In
addition to DRG cells, a few Reg-2-immunoreactive axons were
visible within ganglia at all time points studied, and in wellstained preparations they could be observed running into and
Averill et al. • Reg-2 in Injured Sensory Neurons
J. Neurosci., September 1, 2002, 22(17):7493–7501 7497
Figure 5. Colocalization of Reg-2positive cells 24 hr after sciatic nerve
transection. Immunofluorescent staining of single L5 DRG sections using
Reg-2 (A, C, E) and IB4-FITC conjugate ( B) or P2X3 ( D) or trkA ( F) polyclonal antibodies 24 hr after sciatic
nerve transection. Arrows show doublelabeled cells, and arrowheads show Reg2-positive cells that are negative for the
second marker. Note that many Reg-2positive cells show IB4 or P2X3 labeling. Scale bar, 50 m.
within the spinal nerve (Fig. 1 E–G). However, only a few immunoreactive axons were present within dorsal roots (Fig. 1 H),
which suggests that Reg-2 protein from DRG cells is transported
peripherally but mainly not centrally after nerve injury. This
conclusion was supported by analysis of the central termination
territory of DRG axons and of the effect of nerve ligation.
Immunostaining of lumbar spinal cord after sciatic nerve transection revealed the previously described expression of Reg-2 in
motor neurons (Livesey et al., 1997) that remained only for the
period of regeneration. Despite upregulation of Reg-2 in the
DRG, as described above, no staining was observed in the dorsal
horn of the spinal cord (Fig. 3A–D) or in the dorsal column nuclei
(Fig. 3 E, F ) at any time points studied (1, 7, and 30 d). Accumulation of Reg-2 immunoreactivity was observed proximal to a
ligature of the sciatic nerve (Fig. 4 B, D,F ) or saphenous nerve
(a purely sensory nerve), but very little was present proximal to a
dorsal root ligature (Fig. 4 A, C,E).
The population of small-diameter Reg-2-positive neurons
observed in L5 lumbar DRG 24 hr after sciatic nerve injury
coexists almost exclusively (⬎95%) with IB4 binding and purinoreceptor P2X3 immunoreactivity (Fig. 5A–D, Table 2). IB4
binding and P2X3 expression have been shown to coexist in that
⬃98% of P2X3-expressing sensory neurons are IB4-positive (Bradbury et al., 1998). At this same 24 hr time point, a proportion of the
L5 DRG Reg-2-positive profiles (21% after transection and 25%
after nerve crush) also colabel for the nerve growth factor (NGF)
receptor trkA (Fig. 5 E, F ). Numerous DRG cells showed galanin
immunoreactivity, but there was little coexistence with Reg-2
(Table 2).
At 7 d after sciatic nerve injury (both transection and crush),
Reg-2 coexpression with IB4 binding was much reduced (Fig.
6 A, B, Table 2), but a large proportion of the Reg-2immunoreactive profiles showed immunoreactivity for galanin
(Fig. 6C,D) and NPY (Fig. 6 E, F ). Both of these peptides have
been shown to be upregulated in sensory neurons after sciatic
nerve injury (Hokfelt et al., 1987; Villar et al., 1989; Wakisaka et
7498 J. Neurosci., September 1, 2002, 22(17):7493–7501
Table 2. The percentage of Reg-2-immunoreactive DRG cells that also
express IB4, P2X3, trkA, galanin, NPY, or ATF3 at various time points
after sciatic nerve transection
Time
point
24 hr
7d
30 d
Markers
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
Reg-2
and
and
and
and
and
and
and
and
and
and
and
and
and
and
and
and
and
and
IB4
P2X3
trkA
galanin
NPY
ATF3
IB4
P2X3
trkA
galanin
NPY
ATF3
IB4
P2X3
trkA
galanin
NPY
ATF3
% of Reg-2expressing cells
that also express
the marker
% of markerexpressing cells that
also express Reg-2
95.3 ⫾ 1.8
94.7 ⫾ 1.9
21.2 ⫾ 2.0
2.2
NA
77.8 ⫾ 1.8
3.2 ⫾ 1.6
20.3 ⫾ 4.9
0.7 ⫾ 0.7
48.6 ⫾ 3.5
76 ⫾ 1.7
96.5 ⫾ 2.6
20.9 ⫾ 10.5
24.7 ⫾ 12.5
11.4 ⫾ 5.7
53.8 ⫾ 11.8
39.8 ⫾ 4.4
71.8 ⫾ 9.5
20.3 ⫾ 3.3
28.2 ⫾ 2.0
5.0 ⫾ 0.2
1.3
NA
7.2 ⫾ 0.2
0.6 ⫾ 0.3
3.2 ⫾ 1.3
0.1 ⫾ 0.1
9.4 ⫾ 1.2
19.8 ⫾ 1.3
7.0 ⫾ 1.0
4.9 ⫾ 2.6
5.3 ⫾ 2.7
2.5 ⫾ 1.3
17.6 ⫾ 1.8
10.6 ⫾ 0.8
7.1 ⫾ 0.3
The numbers shown are mean ⫾ SEM and are based on counts from three animals,
with the exception of the 24 hr Reg-2 and galanin counts, which are based on two
animals. NA, Not applicable.
al., 1991, 1992; Ma and Bisby, 1997). At 30 d, coexistence with
NPY and galanin was still present, and some coexistence with
IB4 was again evident (Table 2).
To determine whether Reg-2 expression was restricted to the
injured sensory neurons, we performed colabeling experiments
for a transcription factor, ATF3, which has been shown to be a
marker for injured DRG neurons (Tsujino et al., 2000). In a
separate set of experiments, the neuronal tracer molecule Fast
Blue [5 l of 5%(w/v)] was injected into the stump of the
transected sciatic nerve to retrogradely label axotomized sciatic
projecting neurons in L4/5 DRG. At all time points examined (1,
7, and 30 d), we found a proportion of Reg-2-positive profiles that
either were ATF3 negative (Fig. 7) or did not contain Fast Blue
tracer (data not shown). Thus 59 –73% of DRG cells showed
ATF3 after sciatic transection (Table 1), and 72–97% of Reg-2
cells showed ATF3 immunoreactivity (Table 2). We conclude
that the population of Reg-2 positive, and ATF3- or Fast Bluenegative, neurons represent uninjured DRG neurons that have
upregulated Reg-2.
DISCUSSION
This analysis of Reg-2 expression has uncovered a dynamic pattern of protein expression that has not been reported previously
in the nervous system. We report here that after peripheral nerve
injury, Reg-2 displays an initial phase (24 hr) of expression in
small-diameter, predominantly nociceptive sensory neurons, but
by 5 d expression has switched from these small-diameter neurons
to a larger-diameter non-nociceptive population. This pattern of
Reg-2 expression has a number of interesting features that make
it quite unique and were not reported in the original study
describing DRG expression (Livesey et al., 1997). First, Reg-2 is
one of a very small number of molecules that are rapidly upregu-
Averill et al. • Reg-2 in Injured Sensory Neurons
lated after nerve injury. Second, Reg-2 is the first example of a
molecule that is selectively upregulated in the IB4/P2X3, GDNFsensitive population of nociceptors. Third, the shift in Reg-2
expression from initially small-diameter to subsequently largediameter neurons is unique and may reflect the selective expression of cytokines and growth factors adjacent to the site of
damage or denervated target (see below). Fourth, Reg-2 is axonally transported predominantly peripherally and not centrally.
Reg-2 is a gene belonging to a larger family of Reg-related
genes. The original member of the family, Reg, was a novel gene
expressed in regenerating pancreatic islet cells (Terazono et al.,
1988) and was found to code for a 16 kDa secretory protein. In
subsequent years, a family of related genes has been described
under a rather varied nomenclature and been broadly categorized
into three groups (for review, see Okamoto, 1999). Type I Reg
proteins include the original Reg-1 protein and have been shown
to have a role in promoting regeneration and proliferation of
insulin-producing -cells of pancreatic islets (Terazono et al.,
1988, 1990; Zenilman et al., 1997; Levine et al., 2000). The type
II Reg gene has been described only in the mouse (Unno et al.,
1993), and the biological function of this gene has not been
determined. Type III Reg proteins, which include rat Reg-2
described here, have been described as growth factors in liver
cells (Christa et al., 1996), as possible anti-apoptotic agents in
pancreatic acinar cells (Ortiz et al., 1998), and as a novel motor
and sensory neuron survival factor (Livesey et al., 1997; Nishimune et al., 2000). In addition, a regenerative role of Reg-2 as a
Schwann cell mitogen released at the regrowing axon tip has been
described (Livesey et al., 1997).
Sensory neurons of the DRG can be categorized into subpopulations according to their size and expression of various neurochemical markers (for review, see Snider and McMahon, 1998;
Hunt and Mantyh, 2001). Small-diameter sensory afferents represent ⬃70% of the total lumbar DRG neuron population, have
unmyelinated axons (C-fibers), and act mainly as nociceptors.
The large-diameter afferents of the neuron population have myelinated axons (A-fibers), innervate mechanoreceptors peripherally, and mediate proprioceptive and tactile responses. They
can be immunocytochemically identified using antibodies that
recognize high molecular weight neurofilament protein. Smalldiameter DRG neurons can be further characterized into a
peptide-expressing [such as calcitonin-related gene product
(CGRP) and substance P] and NGF-responsive subset and a
nonpeptidergic, GDNF-responsive subset that bind isolectin-B4
(IB4) and express the purinoreceptor P2X3 (Averill et al., 1995;
Bennett et al., 1998; Priestley et al., 2002).
Peripheral nerve injury induces dramatic changes in gene expression in DRG neurons. For instance, after peripheral nerve
transection or crush, the transcription factors c-jun (Herdegen et
al., 1992; Jenkins et al., 1993) and ATF3 (Tsujino et al., 2000) are
expressed in all injured neurons within 24 hr, whereas the pattern
and extent of the expression of neuropeptides such as galanin and
NPY are dependent on the time after injury (Hokfelt et al., 1987;
Wakisaka et al., 1991; Zhang et al., 1998; Landry et al., 2000).
Endogenous expression of these peptides in normal sensory neurons is limited to a small number (⬍5%) of small-diameter cells,
but after injury expression is robustly enhanced and maintained
in neurons of all sizes.
Reg-2 expression is rarely seen in control ganglia, but both
mRNA (Livesey et al., 1997) and protein (this study) are upregulated after nerve injury. Twenty-four hours after either sciatic
nerve transection or crush, Reg-2 is transiently expressed within
Averill et al. • Reg-2 in Injured Sensory Neurons
J. Neurosci., September 1, 2002, 22(17):7493–7501 7499
Figure 6. Colocalization of Reg-2positive cells 7 d after sciatic nerve transection. Immunofluorescent staining of
single L4/5 DRG sections using antiReg-2 polyclonal antibody (A, C, E) and
IB4-FITC conjugate ( B) or galanin ( D)
or NPY ( F) polyclonal antibodies, 7 d
after sciatic nerve transection. Arrows
show double-labeled cells, and arrowheads show Reg-2-positive cells that are
negative for the second marker. Note
that many Reg-2-positive cells at this
time point show colocalization with
NPY and galanin but not IB4. Scale
bar, 50 m.
a subpopulation of the purinoreceptor P2X3- expressing, GDNFsensitive, small-diameter sensory neurons. At this time point, all
Reg-2-expressing cells show IB4 labeling, and the small percentage (20%) that show trkA labeling is consistent with the reported
overlap between IB4 and trkA (Averill et al., 1995). Many molecules are downregulated after peripheral nerve injury, and the
rapid upregulation that we have observed for Reg-2 has so far
been reported only for galanin and for the transcription factors
c-jun and ATF3. In addition, most molecules that are upregulated
are expressed in either the small trkA-expressing cells or largediameter neurons. Reg-2 is the only molecule, to date, that is
selectively upregulated in the IB4-labeled, GDNF-sensitive population of cells. However, at longer time points, Reg-2 expression
was restricted to medium- to large-diameter sensory neurons,
although some expression in small neurons was observed at 30 d.
Our double-labeling studies, cell size distribution data, and
counts of total percentage of DRG cells that express Reg-2 all
suggest that this change is caused by a shift in Reg-2 expression
from the small- to medium/large-diameter neurons. This shift in
Reg-2 expression is very unusual. Galanin, for example, is expressed in medium- and large-diameter neurons at longer time
points but continues to be expressed in small-diameter neurons.
After peripheral nerve axotomy, brain-derived neurotrophic factor (BDNF) expression is also upregulated in medium- to largediameter sensory neurons (Cho et al., 1998; Michael et al., 1999),
but this is the only cell group that shows upregulation. BDNF
expression in small cells has been reported either to be downregulated (Cho et al., 1998) or to show no significant change
(Michael et al., 1999). In addition, unlike Reg-2, crush injury can
induce an increased expression of BDNF in all cell sizes (Cho et
al., 1998). The pattern of expression seen for Reg-2 is thus unlike
any other peptide, and because similar changes are seen after
both transection and crush, it is likely that similar mechanisms for
Reg-2 upregulation are activated in both injury models.
The dynamic changes in Reg-2 expression that we have observed may indicate that quite different factors control Reg-2
expression, and function, in the small and large DRG cells. For
example, Reg-2 expression in the small-diameter IB4 cells may
Averill et al. • Reg-2 in Injured Sensory Neurons
7500 J. Neurosci., September 1, 2002, 22(17):7493–7501
Figure 7. Colocalization of Reg-2positive profiles with axotomized sciatic
projecting neurons. Immunofluorescent
staining of single L5 DRG sections using Reg-2 (A, C) and ATF3 (B, D) polyclonal antibodies 24 hr after sciatic
nerve transection is shown. Arrows in C
and D show profiles that are double
labeled for Reg-2 and ATF3. Note that
after axotomy, a small number of Reg2-positive profiles do not colocalize
with the injured nerve marker ATF3
(arrowheads). Scale bars, 50 m.
have local functions. The transient expression of Reg-2 may result
in the delivery of a bolus of the peptide to the site of injury, or
Reg-2 could be released within the DRG itself and act on satellite
glia and other neurons. This could account for the appearance of
Reg-2 in neurons that were not axotomized in our experiments,
as well as the lack of transport of the peptide into the dorsal horn.
It has generally been observed that peptides, such as NPY, that
are upregulated within the DRG are exported through the central
axonal processes of the DRG to the dorsal horn and/or dorsal
column nuclei. However, our studies indicate that Reg-2 is transported predominantly peripherally. A similar lack of central
transport has recently been reported for the degenerin/epithelial
sodium channel (DEG/ENaC) family member BNaC1␣ (GarciaAnoveros et al., 2001). A local role for Reg-2 would be consistent
with developmental studies in which Reg-2 appears to act in an
autocrine/paracrine manner. After induction by a peripheral factor (possibly a cytokine of the LIF/CNTF family), Reg-2 can act
on the parent cell or neighboring cells as an obligatory survival
factor (Nishimune et al., 2000). The factor inducing Reg-2 in IB4
cells is not known but could be a member of the LIF/IL-6/CNTF
family because IB4 cells are known to have binding sites for this
family (Thompson et al., 1997). Whether locally released Reg-2 is
responsible for its induction in large neurons is not known but
worth further investigation. Such a role for the IB4 group of
small-diameter neurons would also complement that of the peptidergic, small-diameter, NGF-responsive sensory fibers that have
a well established role in the peripheral inflammatory response
(McMahon, 1996).
Reg-2 expression in medium- to large-diameter sensory neurons 7 d after sciatic nerve section predominantly colocalized
with NPY or galanin. The expression of these neuropeptides in
uninjured DRG neurons is maintained at a low level, and it is
thought that the upregulation in the same neurons after periph-
eral nerve injury enables a change in function of sensory neurons
from one of transduction of peripheral sensory information to one
of survival and regeneration of the damaged neuron. The tonic
release of Reg-2 from the extending growth cones of damaged
large-diameter sensory neurons may serve a similar function. It
has previously been shown that neutralizing Reg-2 activity at the
site of peripheral nerve damage leads to a reduced level of
regeneration (Livesey et al., 1997). This may have been an indirect effect, given that Reg-2 has a mitogenic effect on Schwann
cells, which are crucial for the regenerative process.
In summary, we suggest that Reg-2 expression after injury may
have an important role in the regenerative process, with distinct
functions in small- and large-diameter cells. Reg-2 may act both
locally, after release within the ganglion, and at a distance at the
site of nerve damage and regeneration.
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