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Heat Shock Proteins (HSP):[edit]

Physiological stressors such as heat, oxidative stress, and ATP depletion induce the expression of Heat Shock Protein genes.[1] Expression of the HSP genes is regulated by Heat Shock Transcription Factor Protein (HSF1)[1]. When the HSF1 pathway is activated, monomers of HSF1 oligomerize as homotrimers, go to the nucleus, and bind to the promoter region all DNA which contain the stress-inducible HSP genes[2]. HSP transcripts are translated to functional Heat Shock Proteins.    

HSP and Neurodengereative Diseases:[edit]

HSP facilitate the proper folding of functional proteins and prevent the aggregation of unfolded or mis-folded proteins[3]. In many neurodegenerative diseases, changes in the expression of HSP is said to be the primary cause of rapid onset of the disease[4]. However, induced over-expression of the same HSP has shown to slow down neurodegeneration[4]

HSP and Alzheimers' Disease:[edit]

Prominent indications of Alzheimers' Disease include neurofibrillary tangles (NFT) which are formed by aggregates of the tau protein; or amyloid plaques (neuritic), formed by aggregates of the beta amyloid (aβ) proteins[5].

Tau proteins become hyper-phosphorylated due to minimal supervision from HSP and thus form toxic, insoluble NFT aggregates[6].This causes microtubules in neurons to become unstable and promotes further neurodegenerative damage[6]. Recent studies reveal that increasing the expression of HSP, specifically HSP 90 enhances the degradation and solublization of tau aggregates and promotes refolding back their native confirmation[5][6].

Aβ proteins are fragments of amyloid precursor proteins (APP) and from aggregates of hard, insoluble plaques, also known as neuritic plaques (NP)[4]. These neuritic plaques form spontaneously and are stable over time. They interfere with neural activity which increases neurodegeneration[4]. An HSP 40/70/90 complex inhibits the formation of aβ plaques and slows their rate of aggregation to decrease formation of neuritic plaques[5].

Further studies are being conducted which investigate the role of HSP 90 as a therapeutic target[5][7].

HSP and Parkinsons' Disease:[edit]

Parkinson's Disease results from a loss of dopaminergic neurons in substantia nigra[3]. Loss of dopamine neurons causes α-synuclein proteins to accumulate in the brain in the form of Lewy bodies[3]. HSP 70 is known to inhibit the accumulation of α-synuclein and decrease protein toxicity in the cell[8][9]. HSP 70 also works to prevent apoptosis and protects against early cell death, specifically neuronal cell death[10].

HSP 70 is a potential therapy target to reduce the progression of Parkinson's Disease[7][10].

HSP and Huntington's Disease[edit]

Huntington's disease is a result of an autosomal dominant mutation due to a large number (>40) of trinucleotide repeats (CAG)[3]. The Huntingtin gene codes for the mutant huntingtin protein, htt. This mutant protein forms ubiquitinated neuronal intranuclear inclusions (NII), a form of neural protein aggregates[11].

These NIIs recruit several proteins which accumulate in the cytoplasm of the cell[11]. HSP40 and HSP70 are also recruited to the area to attempt to refold the mutant protein[12]. However, because the htt protein is very long and forms big aggregates, HSP 40 and HSP 70 are unable to exert their normal protective functions due to the vast amount of aggregates. Also, they cannot compete with the fast rate of aggregation[12]. This results in the overwhelming accumulation of misfolded mutant htt proteins over the course of the disease. This accumulation causes in neuronal degeneration in the striatum and the cortex which interferes with coordination and motor skills, which worsen over time[3].

Over-expression of HSP 40 and HSP 70 is a therapy mechanism that is being investigated to treat the symptoms of Huntington's Disease[12].

HSP and Autophaghy[edit]

The HSP chaperone system and Autophagy work together to maintain functional proteins within cells under extreme conditions (excessive stress, starvation). In a process known as chaperone-mediated autophagy[13], HSP target proteins in the cytoplasm which expose a a signature motif. Once the HSP recognize the motif, the protein is bound to a lysosomal associated membrane protein (LAMP2) which causes the protein to unfold and translocate into the lysosome to be degraded[13]. Microautophagy and Macroautophagy are another way for cells to degrade dysfunctional proteins, but are unassociated with HSP. Therefore, in certain conditions, cells prioritize HSP mechanisms over autophagy to completely inhibit other modes of cellular autophagy.[13]

Cardiovascular:[edit]

HSP maintain and stabalize cardiac myocytes to ensure that they are functional and operate at their full potential[1]. In instances where cardiac myocytes suffer an injury (ischemia), HSP are expressed at an elevated rate. [14] For example, damage caused by an increase in reactive oxygen species (ROS), which are a result of cardiac ischemia[14] have detrimental effects on the cell and its cellular components. Antioxidants are a form of protective molecules that cells use in response to high levels of oxidative stress caused by ROS. These antioxidants neutralize the ROS to minimize their damage in the cell while HSP work to repair the damage caused by the ROS in the cells.[15]

  1. ^ a b c Benjamin, I. J.; McMillan, D. R. (1998-07-27). "Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease". Circulation Research. 83 (2): 117–132. ISSN 0009-7330. PMID 9686751.
  2. ^ Hightower, Lawrence E. "Heat shock, stress proteins, chaperones, and proteotoxicity". Cell. 66 (2): 191–197. doi:10.1016/0092-8674(91)90611-2.
  3. ^ a b c d e Wyttenbach A, Arrigo AP. The Role of Heat Shock Proteins during Neurodegeneration in Alzheimer's, Parkinson's and Huntington's Disease. In: Madame Curie Bioscience Database [Internet]. Austin (TX): Landes Bioscience; 2000-2013. Available from: https://www.ncbi.nlm.nih.gov/books/NBK6495/
  4. ^ a b c d Adachi, Hiroaki; Katsuno, Masahisa; Waza, Masahiro; Minamiyama, Makoto; Tanaka, Fumiaki; Sobue, Gen (2009-01-01). "Heat shock proteins in neurodegenerative diseases: Pathogenic roles and therapeutic implications". International Journal of Hyperthermia. 25 (8): 647–654. doi:10.3109/02656730903315823. ISSN 0265-6736.
  5. ^ a b c d Ou, Jiang-Rong; Tan, Meng-Shan; Xie, An-Mu; Yu, Jin-Tai; Tan, Lan (2014-10-13). "Heat Shock Protein 90 in Alzheimer's Disease". BioMed Research International. 2014: 1–7. doi:10.1155/2014/796869. ISSN 2314-6133. PMC 4211323. PMID 25374890.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  6. ^ a b c Hamos, J. E.; Oblas, B.; Pulaski-Salo, D.; Welch, W. J.; Bole, D. G.; Drachman, D. A. (1991-03-01). "Expression of heat shock proteins in Alzheimer's disease". Neurology. 41 (3): 345–350. ISSN 0028-3878. PMID 2005999.
  7. ^ a b Klettner, Alexa (2004-06-01). "The induction of heat shock proteins as a potential strategy to treat neurodegenerative disorders". Drug News & Perspectives. 17 (5): 299–306. ISSN 0214-0934. PMID 15334179.
  8. ^ Turturici, Giuseppina; Sconzo, Gabriella; Geraci, Fabiana (2011-02-24). "Hsp70 and Its Molecular Role in Nervous System Diseases". Biochemistry Research International. 2011: 1–18. doi:10.1155/2011/618127. ISSN 2090-2247. PMC 3049350. PMID 21403864.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  9. ^ Broer, Linda; Koudstaal, Peter J.; Amin, Najaf; Rivadeneira, Fernando; Uitterlinden, Andre G.; Hofman, Albert; Oostra, Ben A.; Breteler, Monique M. B.; Ikram, M. Arfan (2011-11-26). "Association of heat shock proteins with Parkinson's disease". European Journal of Epidemiology. 26 (12): 933–935. doi:10.1007/s10654-011-9635-9. ISSN 0393-2990. PMC 3253286. PMID 22120601.
  10. ^ a b Luo, Guang-Rui; Chen, Sheng; Le, Wei-Dong (2006-10-15). "Are heat shock proteins therapeutic target for Parkinson's disease?". International Journal of Biological Sciences. 3 (1): 20–26. ISSN 1449-2288. PMC 1622889. PMID 17200688.
  11. ^ a b DiFiglia, Marian; Sapp, Ellen; Chase, Kathryn O.; Davies, Stephen W.; Bates, Gillian P.; Vonsattel, J. P.; Aronin, Neil (1997-09-26). "Aggregation of Huntingtin in Neuronal Intranuclear Inclusions and Dystrophic Neurites in Brain". Science. 277 (5334): 1990–1993. doi:10.1126/science.277.5334.1990. ISSN 0036-8075. PMID 9302293.
  12. ^ a b c Hansson, Oskar; Nylandsted, Jesper; Castilho, Roger F.; Leist, Marcel; Jäättelä, Marja; Brundin, Patrik (2003-04-25). "Overexpression of heat shock protein 70 in R6/2 Huntington's disease mice has only modest effects on disease progression". Brain Research. 970 (1–2): 47–57. doi:10.1016/S0006-8993(02)04275-0.
  13. ^ a b c Dokladny, Karol; Myers, Orrin B; Moseley, Pope L. "Heat shock response and autophagy—cooperation and control". Autophagy. 11 (2): 200–213. doi:10.1080/15548627.2015.1009776. PMC 4502786. PMID 25714619.
  14. ^ a b Marber, M. S.; Latchman, D. S.; Walker, J. M.; Yellon, D. M. (1993-09-01). "Cardiac stress protein elevation 24 hours after brief ischemia or heat stress is associated with resistance to myocardial infarction". Circulation. 88 (3): 1264–1272. doi:10.1161/01.CIR.88.3.1264. ISSN 0009-7322. PMID 8353888.
  15. ^ Cumming, K. T. (2014). Heat shock proteins and endogenous antioxidants in skeletal muscle: acute responses to exercise and adaptations to training.
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