**2.1 High molecular weight heat shock proteins**

The HSP70 family is the most highly conserved and best studied class of HSP. Human cells contain several HSP 70 family members – constitutively expressed, inducible, mitochondrial – HSP75, and GRP78, localized in the endoplasmatic reticulum. Under normal conditions HSP70 proteins function as ATP-dependent chaperones, assisting the folding of newlysynthesised proteins, participating in intracellular transport of proteins across cellular membranes. Under stressful conditions the synthesis of inducible HSP70 enhances the ability of cells to cope with the increased levels of denatured proteins. HSP70 blocks caspase-depedent and independent activation of apoptosis (Shi et al,1992; Murakami et al,

Chronic Obstructive Pulmonary Disease - Chaperonopathology 73

molecular size of approximately 800kDa, having up to 40 subunits from two gene products – αA and αB. αA is encoded by and constitutes of 173 aminoacids, while αB is encoded by and has 175 aminoacids and both share 57% sequence similarity. In contrast to αA, αB is also constitutively expressed in various tissues with high rates of oxidative stress – skeletal muscles, brain, heart, kidney (Lowe, 1992). Its primary sequence can be organized in three distinct structural regions: an α-crystallin domain of 90 amino-acids in length which is conserved among all sHSP and flanked by an N- and C – terminal domains of variable length and sequence. The conserved α-crystallin domain spans residues 68-148. It is has seven strands, organized in two sheets. The N - terminal domain is highly variable and influences subunit oligomerization and chaperone-like activity, whereas the C-terminal extension stabilizes the global structure and enhances protein/substrate complex (Sun et al, 1997; Bhatacharyya et al, 2002) αB-crystallin is a major structural protein of human lenses that belongs to the family of small heat-shock proteins. It has auto-kinase activity and participates in intracellular architecture and membrane stabilisation (Nicole et al, 2002; Wang K, Spector A, 1996). It acts as molecular chaperone and stabilises proteins in large soluble aggregates in the cytoplasm. The cytoplasmic expression of αB-crystallin is also responsible for the regulation of cyclin-D1 ubiquitination (Liu et al, 2006) and inhibition of pro-apoptotic proteins such as caspase-3,

Compared to other organs lungs are unique in their exposure to high levels of oxygen. Because of their close contact with the environment the airway epithelium is directly exposed to either exogenous oxidants – (cigarette smoke, airway pollutants), or endogenous ones – generated by phagocytes or other cell types. To keep the balance lungs need efficient adaptive mechanisms that correspond to their physiological functions. If the enzymatic or non-enzymatic antioxidant systems do not provide the corresponding adaptive response

It is still considered that oxidative stress is one of the triggers, contributing to the enhanced

The airspace epithelial surface is particularly vulnerable to the effects of oxidative stress. The injury of the epithelium is an important early event, following exposure to cigarette smoke. The noxious effects of the cigarette smoke on human epithelial cell monolayers has been demonstrated by cell detachment, decreased cell adherence and increased cell lysis (Jones, et al, 1980; Lannan S t al, 1994). It is supposed that these effects are in part oxidant mediated since GSH appears to be critical for the maintenance of the epithelial integrity following exposure to smoke. It is demonstrated in studies that the direct exposure to smoke condensates is associated with profound changes in the homeostais of glutathione (GSH) (Li et al, 1994, 1996). Concentration of GSH are significantly decreased after exposure to cigarette smoke condensate. This is due to a decrease of the activity of the enzymes, responsible for the keeping the redox-cycle – glutathioneperoxidase, glucose-6-phosphate dehydrogenase. In addition the depletion of GSH alone induces airway detachment and

p53, Bax and Bclxs (Mao et al, 2004; Lin et al, 2007)

oxidative stress occurs.

**3. Оxidative stress, COPD and heat shock proteins** 

or abnormal inflammatory response, characteristic for COPD patients.

**3.1 Oxidative stress, chaperones and epithelial injury in COPD** 

increases its permeability (Li et al, 1995; Rahman et al, 1995).

1988;) It participates in the ubiquitination of proteins through its co-chaperones – BAG1 and CHIP. (Meacham et al, 2001; Luders et al, 2000)

The HSP90 family include ATP – dependent chaperones – HSP90α and HSP90β and GRP94. The two isoforms of HSP90 (HSP90α and HSP90β) that are essential to cells are abundantly expressed under normal conditions (Csermely et al, 1998). HSP90 proteins make up 1-2% of the cytosolic proteins and are additionally synthethised during stress. They participate in cell signalling pathways –ligand dependent transcription factors – Glucocorticoid receptor (Nathan et al, 1995); ligand independent transcription factors – Myo-D, tyrosine and serine/threonine kinases (Hartson et al, 1994; Shaknovich et al, 1992). Their chaperone function is almost entirely limited to these transcription factors and signal transducing kinases. HSP90 family members also have anti-apoptotic functions and stimulate the protein triage (Tsubuki et al, 1994; Lewis et al, 2000).

HSP60 is called chaperonin. It is constitutively expressed, found primarily in the mitochondrial matrix, although up to 15% could be cytoplasmically expressed. It is ATPdependent chaperone, protecting the mitochondrial proteins and facilitating the proteolytic degradation of misfolded proteins. The chaperone function of HSP60 is regulated by a cochaperone, known as HSP10 that modulates substrate binding and ATP-ase activity. In the presence of ADP, HSP60 regulates apoptosis, demonstrating both pro- and antiapoptotic functions (Bukau et al, 1998).

### **2.2 Small heat shock proteins**

The small heat shock proteins constitute of a diverse family of ubiquituous intracellular proteins (Arrigo et al, 1998). In human ten different sHSP have been described but only a few of them (HSP27, HSP22 and α-Bcrystallin (HSPB5) are true heat shock proteins expressed in response to stress. sHSP are characterized by small molecular weight (12- 43kDa) and a conserved C-terminal domain (the α-crystallin domain). They share the ability to form globular oligomeric structures with molecular masses ranging between 50-800kDa. The dynamic organization of these proteins is essential for performing their biological activity. It depends on their phosphorylated status which is performed by specific signal transduction pathways. It is generally assumed that stress favors the formation of large oligomers associated with unfolded proteins while phosphorylation does the reverse. Large unphosphorylated oligomers of sHSP have greater potentiality to protect cells through their ability to perform chaperone activity. The formation of small phosphorylated oligomers may be required for the binding of unfolded proteins as well as for the recycling of the larger ones (Kato et al, 1996).
