Cystatin C: Role in Neurodegenerative Diseases

This assignment delves into the multifaceted role of cystatin C in the context of neurodegenerative diseases. It specifically focuses on its contribution to prion angiopathy, CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), and the broader spectrum of protein elimination failure angiopathies (PEFA). The assignment analyzes current research findings and emphasizes the potential therapeutic implications of understanding cystatin C's involvement in these conditions.

Running head: CEREBRAL AMYLOID ANGIOPATHY
Cystatin C and Cerebral Amyloid Angiopathy
Name of the Student
Name of the University
Author Note

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CEREBRAL AMYLOID ANGIOPATHY
Table of Contents
Overview....................................................................................................................................2
Connection between CST3, Cystatin C, and Cerebral Amyloid Angiopathy........................2
Affect of Cystatin C-Cerebral Amyloid Angiopathy on patients, medicine and society.......3
CST3..........................................................................................................................................3
Normal Gene Properties.........................................................................................................3
Function..............................................................................................................................3
Localisation........................................................................................................................3
Structure.............................................................................................................................4
Expression..........................................................................................................................4
Regulation..........................................................................................................................4
Gene Dysfunction...................................................................................................................5
Animal Model........................................................................................................................5
Cystatin C Protein......................................................................................................................5
Primary structural properties of Cystatin C...........................................................................6
Secondary Tertiary And Quaternary Structural Properties....................................................6
Biomedical Research Of Cystatin C......................................................................................8
References..................................................................................................................................9

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CEREBRAL AMYLOID ANGIOPATHY
Overview
Connection between CST3, Cystatin C, and Cerebral Amyloid Angiopathy
The cystatin C or γ trace is a group of proteinase inhibitors and is present in the body
fluids of all mammals. In vitro experiments have confirmed cystatin has a capacity of
regulating the activity of the cysteine protease (plays important role in intracellular
catabolism of peptides and proteins). Cystatin C regulates the activity of cysteine proteases
by inhibiting their activity. They are mainly active upon cysteine proteases like cathepsins B,
H, K, L and S. Moreover, cystatin C is proteolytically degraded by cathepsin D and elastase.
Cathepsins are lysosomal proteases commonly known as housekeeping genes and they vary
in their substrate-specificities, structure and biochemical functions. The uncontrolled
proteolysis of cystatin C due to imbalance in active proteases and their endogenous inhibitors
lead to the generation of several debilitating diseases such as multiple sclerosis, muscular
dystrophy, Alzheimer disease (AD), rheumatoid arthritis, ischemia, renal failure,
osteoporosis, inflammatory disease and various other types of cancer (1).
Cerebral Amyloid Angiopathy (CAA) is an autosomal dominat disease. It is a
combination of amyloidosis with hereditary cerebral hemorrhage and is commonly known as
hereditary cystatin C amyloid angiopathy (HCCAA). In this diseases, the amyloid deposition
in the cerebral/ spinal arteries and arterioles leads to the generation of recurrent hemorrhagic
strokes generating severe brain damage, leading to fatal stroke. Leu68Gln variant of cystatin
C gene is the principal component of the amyloid fibrils. A heterozygous point mutation, in
the cystatin C gene is responsible for this CAA autosomal dominant disease. Such
heterogeneous point mutation results in a truncated version of the cystatin c gene from the
amio terminal domain. The truncated protein is not being recognized by the elastase or a

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CEREBRAL AMYLOID ANGIOPATHY
serine protease and this lead ot protein misfolding and subsequent deposition over the
cerebral/spinal arteries as amyloid fibrils (2).
CST3 is commonly known as human cystatin C gene. It is located in chromosome 20
and its mutation is responsible for hereditary cystatin C amyloid angiopathy (3).
Affect of Cystatin C-Cerebral Amyloid Angiopathy on patients, medicine and society
CAA is regarded as the morphologic hallmarks of Alzheimer disease (AD). However,
its presence has been detected in the CT scan of elderly patients who are neurologically
healthy. While majorly asymptomatic, CAA may often lead to intracranial hemorrhage (ICH)
and dementia. Moreover, ICH is the most recognized result of CAA.
It has a profuse impact on the society, mostly over the senior citizens and thus
impacting the elderly care program. Magnetic Resonance Imaging (MRI) is one the principal
technique used for the detection of the CAA (1).
CST3
Normal Gene Properties
Function
Human Cystatin C Gene or CST3 is found in mammals. It belongs to a group of proteinase
inhibitors and regulate the mode of action of cysteine proteinases by inhibiting their activity
(4).
Localisation
It is located in chromosome number 20 in humans (4).

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CEREBRAL AMYLOID ANGIOPATHY
Structure
CST3 gene is composed of three exons and two intron sequences. The introns has a
sequence of 2252 and 1254 bp respectively. The resulting gene size is 4.3 kb approx. The
introns are located in between the nucleotide triplets encoding amino acid residues 55-56 and
93-94 of the mature protein respectively. The respective positions of the introns are identical
with cystatin SN and cystatin SA genes. However, the first intron of CST3 is comparatively
bigger than the first introns present in the cystatin SN and cystatin SA genes (4).
Expression
The CST3 is expressed throughout the body fluid and seminal plasma detected the
highest concentration of CST3 genes. The body fluid circulated throughout the body and
deliver CST3 uniformly. However, the major infiltration is seen in liver, kidney, small
intestine, antrum, stomach, lung, placenta and seminal vesicle. There are certain non-tissue
specific expression of CST3 and this is attributed to the its 5'-flanking region. It shares
identical properties with the promoter domain of 'housekeeping genes.
Three cystatin loci namely CST1 (cystatin SN), CST2 (cystatin SA) and CSTP1 (a
cystatin pseudogene) together constitute CST3 (5).
Regulation
The expression of CST3 is increase in the facial nucleus under the influence of the
several pathological conditions and majorly in axotomy. Other predominant cell type
responsible CST3 expression is microglia and not astrocyte or neuron. The up-regulation of
cystatin C by microglia or hyperplasia of microglia to be presice leads to the expression of
the CST3. Microglia significantly proliferate in during brain injuries such as axotomy or stab
wound and this lead to the overall expression of the CST3 gene. On the other hand, it can also
be stated that CST3 controls the turn-over of intracellular cytosolic proteins of microglia (6).

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CEREBRAL AMYLOID ANGIOPATHY
Gene Dysfunction
Mutation in the amino terminal domain of the CST3 gene results in the protein
misfolding during the post translational modification. Such misfolding results in the
deposition of the CST protein in the form of amyloid fibrils in the brain and neurons. CST3 is
also foun97d being codeposited in the amyloid plaques of Alzheimer's disease or Down's
syndrome (7).
Animal Model
The CST3 gene of mammals shows structural similarity with the Cystatin C gene of
the mice. Such animal model has been extensively utilized in research for the study of the
disease prognosis. It is used as a disease model for Alzheimer’s disease, marker for renal
function affected by cystatin C and as a cerebral hemorrhage model (8).
Cystatin C Protein
Normal Protein Function And Role In Human Biology
The cystatin C or γ trace is a group of proteinase inhibitors. It is widely distributed
inside the body fluids of all mammals and is ubiquitous in nature. Cystatin C regulates the
activity of the cysteine protease, which plays an important role in intracellular catabolism of
peptides and proteins. Cystatin C mainly regulates the activity of cysteine proteases via
inhibiting their function. They are mainly active upon cysteine proteases like cathepsins B, H,
K, L and S. Moreover, cystatin C undergoes proteolytic degradation by cathepsin D and
elastase. Cathepsins are lysosomal proteases and are popularly known as housekeeping genes
and they differ in their primary structural symmetry, substrate binding specificities and
biochemical characteristics.

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CEREBRAL AMYLOID ANGIOPATHY
Cystatin C or cystatin C gene to be precise is widely used as a biomarker of normal
renal function. It also plays a major role in the onset or in the deterioration of the
cardiovascular disease (1).
Primary structural properties of Cystatin C
Cystatin C belongs to the cystatin superfamily. It interacts reversibly with target
peptidases and such interactions is seemingly independent and depends only on the affinity
contributions from a wedge-shaped binding region that is constructed with the help of the two
loop-forming inhibitor segments and a corresponding binding region corresponding to the N-
terminal segment of that particular inhibitor.
It is composed of 120-residue of non-glycosylated polypeptide chain. The cystatin C
gene exists as a single copy of 5 kb (approx) in the human genome The amino-acid sequences
of low-molecular weight in the cystatin family have significant homology with each other.
However, the post-translational modification of each family of cystatin gene (alpha, beta and
gamma) is different from each other. Such different approach in the post translational
modification depends on their localizations and different biological functions (4).
Secondary Tertiary And Quaternary Structural Properties

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CEREBRAL AMYLOID ANGIOPATHY
Figure: 3D structure of Cystatin protein
(Source: 9)
The two Cystatin molecules (as displayed in picture A and B) has canonical cystatin fold,
(N)–b1– a–b2–L1–b3–AS–b4–L2–b5–(C), with a five-stranded antiparallel b-sheet gripped
around a long alpha helix. The appending structure (AS) is broad and irregular. It is
positioned at the opposite end of the beta sheet relative to the N-terminus⁄ loop L1 ⁄ loop L2
edge. Such specialized structural symmetry is known as papain-binding epitope. b1 is the one
of the shortest elements out of the rest standard five antiparallel beta platted sheet. It
comprises of two residues. In both the molecules displayed in the picture, the first 11 residues
are completely disordered. The following two AS residues, which differ in each molecule are
found to be Proline78-Leucine79 in A and Leucine80-Aspartate81 in B. Some of the disulfide
bridges exists in a partially broken form in the tertiary structure (9).
Protein Dysfunction and CAA

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CEREBRAL AMYLOID ANGIOPATHY
The mutation in the one of the three exons of cystatin protein results in the occurance
of the CAA disease. This mutation occurs in the luciene residue causes at 68th position in the
gene. Leu68Gln variant of cystatin C gene is the principal component of the amyloid fibrils.
A heterozygous point mutation, in the cystatin C gene is responsible for this CAA autosomal
dominant disease. Such heterogeneous point mutation results in a truncated version of the
cystatin c gene from the amio terminal domain. The truncated protein is not being recognized
by the elastase or a serine protease and this lead ot protein misfolding and subsequent
deposition over the cerebral/spinal arteries as amyloid fibrils (10).
Biomedical Research Of Cystatin C
Three cystatin loci namely CST1 (cystatin SN), CST2 (cystatin SA) and CSTP1 (a
cystatin pseudogene) together constitute CST3 (5)(11).
There are extensive biomedical research that has been carried on Cystatin in order to
ascertain the actual reason and the principal stigma behind the prognosis of CAA, a disease
prevalent in elderly people. In order to study the effect and the intensity of the mutation and
subsequent protein misfolding on the disease prognosis, several animal model, mainly mouse
have been designed and studies extensively.
Though significant studies have been undertaken in this field, but keeping the
complexity of the disease in mind, further through research in the field centering the point
specific mutation of CST3 gene and its effects on CAA is required (12).

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CEREBRAL AMYLOID ANGIOPATHY
References
1. Carare RO, Hawkes CA, Jeffrey M, Kalaria RN, Weller RO. cerebral amyloid
angiopathy, prion angiopathy, CADASIL and the spectrum of protein elimination
failure angiopathies (PEFA) in neurodegenerative disease with a focus on therapy.
Neuropathology and applied neurobiology. 2013 Oct 1;39(6):593-611.
2. Yamada M, Naiki H. Cerebral amyloid angiopathy. Progress in molecular biology and
translational science. 2012;107:41-78.
3. Lamontagne M, Timens W, Hao K, Bossé Y, Laviolette M, Steiling K, Campbell JD,
Couture C, Conti M, Sherwood K, Hogg JC. Genetic regulation of gene expression in
the lung identifies CST3 and CD22 as potential causal genes for airflow obstruction.
Thorax. 2014 Sep 2:thoraxjnl-2014.
4. Turk V, Stoka V, Vasiljeva O, Renko M, Sun T, Turk B, Turk D. Cysteine cathepsins:
from structure, function and regulation to new frontiers. Biochimica et Biophysica
Acta (BBA)-Proteins and Proteomics. 2012 Jan 31;1824(1):68-88.
5. Magister Š, Kos J. Cystatins in immune system. Journal of Cancer. 2013;4(1):45.
6. Dutta G, Barber DS, Zhang P, Doperalski NJ, Liu B. Involvement of dopaminergic
neuronal cystatin C in neuronal injury‐induced microglial activation and
neurotoxicity. Journal of neurochemistry. 2012 Aug 1;122(4):752-63.
7. Krunic AL, Stone KL, Simpson MA, McGrath JA. Acral peeling skin syndrome
resulting from a homozygous nonsense mutation in the CSTA gene encoding cystatin
A. Pediatric dermatology. 2013 Sep 1;30(5).
8. Togashi Y, Sakaguchi Y, Miyamoto M, Miyamoto Y. Urinary cystatin C as a
biomarker for acute kidney injury and its immunohistochemical localization in kidney

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in the CDDP-treated rats. Experimental and toxicologic pathology. 2012 Nov
30;64(7):797-805.
9. Kolodziejczyk R, Michalska K, Hernandez‐Santoyo A, Wahlbom M, Grubb A,
Jaskolski M. Crystal structure of human cystatin C stabilized against amyloid
formation. The FEBS journal. 2010 Apr 1;277(7):1726-37.
10. Rajagopalan P, Refsum H, Hua X, Toga AW, Jack CR, Weiner MW, Thompson PM,
Alzheimer's Disease Neuroimaging Initiative. Mapping creatinine-and cystatin C-
related white matter brain deficits in the elderly. Neurobiology of aging. 2013 Apr
30;34(4):1221-30.
11. Premachandra HK, Wan Q, Elvitigala DA, De Zoysa M, Choi CY, Whang I, Lee J.
Genomic characterization and expression profiles upon bacterial infection of a novel
cystatin B homologue from disk abalone (Haliotis discus discus). Developmental &
Comparative Immunology. 2012 Dec 31;38(4):495-504.
12. Liu Y, Cai H, Wang Z, Li J, Wang K, Yu Z, Chen G. Induction of autophagy by
cystatin C: a potential mechanism for prevention of cerebral vasospasm after
experimental subarachnoid hemorrhage. European journal of medical research. 2013
Jul 1;18(1):21.