Molecular chaperones, evolution and medicine

Contribution of Extracellular Vesicles and Molecular Chaperones in Age-Related Neurodegenerative Disorders of the CNS

Many neurodegenerative disorders are characterized by the abnormal aggregation of misfolded proteins that form amyloid deposits which possess prion-like behavior such as self-replication, intercellular transmission, and consequent induction of native forms of the same protein in surrounding cells. The distribution of the accumulated proteins and their correlated toxicity seem to be involved in the progression of nervous system degeneration. Molecular chaperones are known to maintain proteostasis, contribute to protein refolding to protect their function, and eliminate fatally misfolded proteins, prohibiting harmful effects. However, chaperone network efficiency declines during aging, prompting the onset and the development of neurological disorders. Extracellular vesicles (EVs) are tiny membranous structures produced by a wide range of cells under physiological and pathological conditions, suggesting their significant role in fundamental processes particularly in cellular communication. They modulate the behavior of nearby and distant cells through their biological cargo. In the pathological context, EVs transport disease-causing entities, including prions, α-syn, and tau, helping to spread damage to non-affected areas and accelerating the progression of neurodegeneration. However, EVs are considered effective for delivering therapeutic factors to the nervous system, since they are capable of crossing the blood-brain barrier (BBB) and are involved in the transportation of a variety of cellular entities. Here, we review the neurodegeneration process caused mainly by the inefficiency of chaperone systems as well as EV performance in neuropathies, their potential as diagnostic biomarkers and a promising EV-based therapeutic approach.

Heat injury to cells in perfused systems

Tissue injury in response to excessive heat results in a clinical burn. Burns cause a range of physiologic derangements, including denaturation of macromolecular structures, leakage of cell membranes, activation of cytokines, and cessation of blood flow, all leading to tissue death. The purpose of this paper is to examine the mechanisms and consequences of burn injury and to discuss potential therapies based on these mechanisms. Knowledge of the thermal properties of tissues can predict the time-temperature relationship necessary to cause a specified thermal insult. Changes in cell membrane biochemistry and the stabilization of proteins through the heat-shock response can enable biomacromolecules to withstand supraphysiological temperatures. Mechanisms of cellular repair allow recovery of cellular function after thermal insult. An understanding of the response of proteins, cellular organelles, and cells to heat provides the foundation for understanding the pathophysiology and treatment of burn injury. The physics, biochemistry, and cellular biology behind the host response to thermal injury in perfused systems are reviewed.

STRESS PROTEIN EXPRESSION KINETICS

In all organisms there is an elevated synthesis of a select family of "stress proteins" in response to a broad array of environmentally driven stress vectors including elevated or depressed temperature, changes in pH, treatment with many classes of chemicals, ischemia, desiccation, and UV irradiation. The presence of stress proteins, often termed heat shock proteins (HSPs), has been recognized for more than four decades, and there is an extensive literature that addresses the structure and properties of HSPs, their function in normal and injured cells and tissues, and the molecular mechanisms of HSP expression in response to stress. Owing to this substantial aggregate of research, there is a growing appreciation of the potential for manipulating the magnitude and timing of elevated HSP expression to achieve targeted therapeutic objectives. The successful realization of this potential requires an understanding of the kinetics of the HSP expression process in response to sublethal stress regimens along with the ability to model the governing events in the process to design practical protocols that could be applied in therapeutic settings. Significant progress has been made in recent years in defining and developing capabilities in these two areas.

Enhancement of complement-induced cell lysis: a novel mechanism for the anticancer effects of Hsp90 inhibitors

Molecular chaperones (heat shock proteins, Hsp-s) play a pleiotropic role in immunological functions. Hsp-s participate in the presentation of peptide antigens, folding of several immunologically important proteins, such as the MHC, and in the maintenance of the activation-competent conformation of key signaling molecules (mostly serine/threonine and tyrosine kinases) of B and T cells activation. The most abundant cytoplasmic chaperone, Hsp90, is in the center of these processes. In recent years Hsp90 inhibitors emerged as very promising anticancer agents. Not surprisingly, Hsp90 inhibitors behave as immunosuppressants, and also cause an induction of superoxide production. Here we extend our previous data by showing the enhancement of complement-induced lysis of several types of tumor cells after Hsp90 inhibition. This novel mechanism may significantly contribute to the anticancer effects of Hsp90 inhibitors in vivo.