“촛불시민이 옳았다. 괴담은 이명박 정부와 관변 과학자들이 퍼트렸다.”는 주장을
뒷받침할만한 광우병 관련 새로운 연구결과가 나왔습니다.

잠복기 상태의 광우병의 발병기전에 대한 기존 가설을 뒤집는 새로운 연구결과가
미국 병리학회지(The American Journal of Pathology) 2012년 8월호에
실렸습니다.

기존 가설에서는 변형 프리온 단백질이 일단 중추신경계(central nervous system,
CNS)를 감염시킨 이후에 자율신경계(autonomic nervous system, ANS)를 감염
시킬 수 있다고 설명했지요.

일본에서 20개월 이하 미국산 쇠고기만을 수입하는 근거가 21개월에서 발생한 광우병
소가 가장 어린 소였기 때문이었는데… 이번 실험에서는 감염시킨지 16개월 만에
흉추와 요추에 위치한 교감신경(자율신경계)에서 광우병 변형 프리온이 검출된 송아지도
확인되었습니다.

뇌를 중심으로 한 중추신경계가 아니라 자율신경계를 통해서 광우병 변형 프리온이 뇌에
도달하기 전에 널리 퍼질 수 있다는 연구결과는 쇠고기 수입위생조건과 식품안전에 아주
중요한 시사점을 주고 있습니다.

연구내용을  내용을 구체적으로 살펴보면 다음과 같습니다.

독일의 로엠에 소재한 프리드리히-뢰플러 연구소의 신종 전염병 연구센터의
Martin H. Groschup 박사가 이끄는 연구팀은 광우병의 발병기전을 연구하기 위해
4~6개월령의 송아지 56마리에 경구로 광우병에 걸린 소에게서 추출한
변형프리온을 경구로 주입하였습니다.

이번 연구팀을 이끈 Groschup 박사는 지난 2005년 Buschmann 박사와 함께
살코기(근육)에도 광우병 변형 프리온 축적이 확인되었다는 동물실험 결과를
발표한 바 있으며(Buschmann, A & Groschup M. H. (2005). Journal of Infectious
Disease. 192, 934-942 )… 올해 2월에도 비정형 광우병 소의 골격근육(살코기)에서
감염력을 확인했다는 연구결과(Suardi S, Vimercati C, Casalone C, Gelmetti D, Corona
C, et al. (2012) Infectivity in Skeletal Muscle of Cattle with
Atypical Bovine Spongiform Encephalopathy. PLoS ONE 7(2): e31449.
doi:10.1371/journal.pone.0031449)를 발표하기도 했습니다.

연구진은 80마리의 송아지에겐 소의 연수에서 추출한 광우병에 감염되지 않은 정상
프리온을 경구로 주입하였습니다.

또한 연구진은 자연적으로 광우병에 감염되어 사망한 소에게서 뽑아낸 샘플을
포함시켰습니다. 조직샘플은 감염시킨지 16개월~44개월 이후의 소의 위장관,
중추신경계, 말초신경계에서 4개월 간격으로 추출하였습니다.

이들 샘플들은 면역조직화학법(immunohistochemistry)의 변형 프리온의 존재
유무를 검사했구요, 광우병 감염에 고도로 민감하게 형질전환된 실험용 생쥐에게
감염시키는 방법도 함께 사용했지요.

대부분의 모든 샘플의 위장관에서 병리학적으로 프리온 단백질이 축적되는 것이
뚜렷하게 관찰되었고… 감염시킨지 16개월 이후부터 흉추와 요추에 위치한
교감신경(자율신경계)에서 광우병 변형 프리온이 검출되었습니다.

그리고 감염시킨지 20개월 이후 부터는 천추와 연수 부위의 부교감신경(자율신경계)
에서 광우병 변형 프리온이 검출되었습니다.

이들 샘플에서 중추신경에서는 변형 프리온이 검출되지 않거나 광우병 임상증상이
나타나지 않았습니다.

따라서 광우병 감염 초기 자율신경계의 교감신경이 부교감신경 보다 더 광범위하게
발병기전에 관여한다는 점이 밝혀졌구요… 소의 경우 변형 프리온 단백질이 교감
신경에 고농도로 축적되었을 때에 부교감신경에 축적되었을 때보다 더 임상증상이
잘 나타난다는 사실도 밝혀졌습니다.

뇌의 연수부위에서 변형 프리온이 검출된 가장 이른 시기는 감염시킨지 24개월
이후로 나타났습니다.

그러나 한 마리에서는 감염시킨지 16개월 이후에 척수에서 변형 프리온 단백질이
검출되었기 때문에 변형 프리온이 뇌로 이동하는 또 다른 경로가 있다는 점을
암시하고 있습니다.

이번 연구를 이끈 Groschup 박사는 “교감신경계가 소의 광우병 발병기전에서 중요한 역할을 한다는 점을 실험을 통해 명백히
보여주었다.”며 “그럼에도 불구하고
우리의 연구결과는 광우병 초기 발병에서 부교감신경 경로가 존재한다는 예전의
연구결과 또한 지지하고 있다”고 밝혔습니다.

또한 그는 “이번 실험결과는 변형 프리온 단백질이 뇌로 올라가는 신경 경로가 교감신경, 부교감신경, 척수의 3가지 경로가
있다는 점을 밝혀냈다.”면서 “우리의
연구결과에서 광우병 초기 잠복기의 병리기전을 명백히 밝혀냄에 따라 초기 광우병
진단 전략과 식품안전 조치에 중요한 시사점을 던졌다”고 덧붙였습니다.


============

Martin Kaatz, Christine Fast, Ute Ziegler, Anne Balkema-Buschmann,
Bärbel Hammerschmidt, Markus Keller, Anja Oelschlegel, Leila McIntyre,
Martin H. Groschup. Spread of Classic BSE Prions from the Gut via the
Peripheral Nervous System to the Brain. The American Journal of
Pathology, 2012; DOI: 10.1016/j.ajpath.2012.05.001

abstract

An experimental oral bovine spongiform encephalopathy (BSE) challenge study was performed to elucidate the route of infectious prions from the gut to the central nervous system in preclinical and clinical infected animals. Tissue samples collected from the gut and the central and autonomic nervous system from animals sacrificed between 16 and 44 months post infection (mpi) were examined for the presence of the pathological prion protein (PrP^Sc) by IHC. Moreover, parts of these samples were also bioassayed using bovine cellular prion protein (PrP^C) overexpressing transgenic mice (Tgbov XV) that lack the species barrier for bovine prions. A distinct accumulation of PrP^Sc was observed in the distal ileum, confined to follicles and/or the enteric nervous system, in almost all animals. BSE prions were found in the sympathetic nervous system starting at 16 mpi, and in the parasympathetic nervous system from 20 mpi. A clear dissociation between prion infectivity and detectable PrP^Sc deposition became obvious. The earliest presence of infectivity in the brain stem was detected at 24 mpi, whereas PrP^Sc accumulation was first detected after 28 mpi. In summary, our results decipher the centripetal spread of BSE prions along the autonomic nervous system to the central nervous system, starting already halfway in the incubation time.

=================

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ajpmedia@elsevier.com. Journalists wishing to interview the authors
may contact Elke Reinking, Public Relations,
Friedrich-Loeffler-Institut at +49 3835171244 or
elke.reinking@fli.bund.de.


About The American Journal Of Pathology The American Journal of
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American Society for Investigative Pathology, seeks to publish
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Subject: Spread of Classic BSE Prions from the Gut via the Peripheral
Nervous System to the Brain


Spread of Classic BSE Prions from the Gut via the Peripheral Nervous
System to the Brain


Martin Kaatz,* Christine Fast,* Ute Ziegler,* Anne Balkema-Buschmann,*
Bärbel Hammerschmidt,* Markus Keller,* Anja Oelschlegel,† Leila
McIntyre,* and Martin H. Groschup*


From the Institute for Novel and Emerging Infectious Diseases,*
Friedrich-Loeffler-Institute, Greifswald-Isle of Riems, Germany; and
the Scripps Institute,† Florida



An experimental oral bovine spongiform encephalopathy (BSE) challenge
study was performed to elucidate the route of infectious prions from
the gut to the central nervous system in preclinical and clinical
infected animals. Tissue samples collected from the gut and the
central and autonomic nervous system from animals sacrificed between
16 and 44 months post infection (mpi) were examined for the presence
of the pathological prion protein (PrPSc) by IHC. Moreover, parts of
these samples were also bioassayed using bovine cellular prion protein
(PrPC) overexpressing transgenic mice (Tgbov XV) that lack the species
barrier for bovine prions. A distinct accumulation of PrPSc was
observed in the distal ileum, confined to follicles and/or the enteric
nervous system, in almost all animals. BSE prions were found in the
sympathetic nervous system starting at 16 mpi, and in the
parasympathetic nervous system from 20 mpi. A clear dissociation
between prion infectivity and detectable PrPSc deposition became
obvious. The earliest presence of infectivity in the brain stem was
detected at 24 mpi, whereas PrPSc accumulation was first detected
after 28 mpi. In summary, our results decipher the centripetal spread
of BSE prions along the autonomic nervous system to the central
nervous system, starting already halfway in the incubation time.



snip…



Concerning the involvement of the different parts of the ANS during
the early spread of the infectious agent, the most interesting results
were found in the youngest animals of our study. Both animals at 16
mpi showed BSE infectivity in sympathetic projections (GCC and
splanchnic nerves). In addition, one of these cows revealed
infectivity in the spinal cord most likely as a result of the
sympathetic spread. The parasympathetic tissues were free of
infectivity in these animals, whereas both cows sacrificed at 20 mpi
contained BSE prions only in the parasympathetic nervous system
(cervical vagus nerve and nodose ganglion) but not in purely
sympathetic projections or in spinal cord. To our knowledge, this is
the first report describing the presence of infectivity in the ANS
before the involvement of the CNS in several peripheral neural tissues
between 16 and 20 mpi in BSE-infected bovines. These results clearly
indicate that both pathways are involved in the early pathogenesis of
BSE, but not necessarily simultaneously. Our theory is supported by
the coexistence of either none or only spurious amounts of infectivity
in the CNS and a remarkable involvement of the sympathetic fibers in
cows slightly later in the incubation period.



In addition to the more frequent involvement of the sympathetic
samples, a higher transmission rate compared with the parasympathetic
samples is obvious. Considering all these results, it is tempting to
assume a more dominant and crucial role of the sympathetic nervous
system in the pathogenesis of BSE in cattle. The delayed onset of
disease in sympathectomized mice infected with scrapie is indicative
for this pathway as well.25 Although our results are in accordance
with previous studies showing a spread along the CMGC and the
splanchnic nerves, notably, our data favor a further distribution via
the sympathetic ganglia chain, including the stellate ganglia and the
GCC. The occurrence of a mild PrPSc accumulation in the brain stem in
association with infectivity solely in sympathetic structures (IT24,
24 mpi) supports the importance of the sympathetic spread. Hence, a
mandatory involvement of the intermediolateral column of the spinal
cord is not observed. The detection of infectivity in the spinal cord
of one animal at 16 mpi indicates a third, additional pathway to the
brain as a result of the dissemination along the sympathetic
splanchnic nerve. Moreover, we suspect a critical role of the
comprehensively involved GCC, because the location close to the brain
provides sympathetic fibers to almost all cranial nerves and possibly
results in an effect on the brain in uncommon (formatio reticularis
and nucleus motorius nervi trigemini) or parasympathetic-related areas
(dorsal motor nucleus of the vagus nerve and nucleus tractus
solitarii), as the initial PrPSc depositions in the CNS shown herein.



Nevertheless, our results also support the previously postulated early
parasympathetic route of the BSE agent along the vagus nerve and the
nodose ganglion, although to a lesser degree than the sympathetic
structures. Furthermore, infectivity of the nodose ganglion before CNS
involvement presumes a centripetal spread along sensory fibers of the
vagus nerve, which are in contrast to the assumption that the
vagus-associated nodose ganglion might be affected via the centrifugal
spread.26 Taken together, our results indicate that there are three
independent possible neuronal ascension routes for BSE prions (in
order of putative importance): sympathetic parasympathetic spinal cord
projections.



Results from scrapie studies in hamster and sheep determined CMGC to
be a part of the sympathetic circuitry, which also contains
parasympathetic fibers21,22,24 as a possible route of ascension of the
agent to the CNS. Our analysis revealed infectivity in the CMGC
already from 16 mpi for both possible centripetal routes, leading to
the question of where the initial determination of infected fibers
takes place. We assume that the route toward the brain likely depends
on the nerve type initially infected at the ENS. Sensory fibers of the
vagus nerve were found widely distributed in the gut.27,28
Furthermore, vagal efferent synapses in intrinsic ganglia of the ENS
innervate the intestinal wall, including the mucosa and submucosa.29
However, a more extensive sympathetic presence in the ENS30 and the
CMGC31 and wide innervations of lymphoid structures by the sympathetic
nervous system32–34 were reported. These facts could explain the wider
and earlier involvement of the sympathetic fibers, as previously
discussed. Furthermore, it cannot be excluded that the CMGC may
influence the route of infection by the close contact of both
sympathetic and parasympathetic nerve types within this ganglion as an
operating center of the ANS.



In summary, our data prove an early and widespread distribution of
infectivity in the ANS in preclinical cattle before an infection of
the CNS. This study is able to confirm the assumed spread via
sympathetic and parasympathetic structures for the BSE agent (Figure
4), but we determined a more crucial role of the sympathetic nervous
system in the initial neuronal distribution. However, both pathways
could be separately involved. According to our results, the spinal
cord seems to represent an additional route of ascension, in addition
to the more prominent pathways of the ANS.



snip…see full text @



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