Progress, Pioneers and Process

Studies in Physiology and Genetic Medicine

Moyra Smith

• Publisher: WSPC
• Year: 2018
• eBook ISBN: 9789813270596
• Topic: Biological Sciences
• Subtopic: Human Anatomy & Physiology
• Index: Biological Sciences

This book describes the growth of information on specific aspects of physiology and pathology of particular disorders and provides an analysis of the processes and contributions of pioneers to discovery. It begins primarily in the second half of the 19th century and explores specific contributions of researchers through to the 20th and 21st centuries. The book revisits specific aspects of physiology, biochemistry and molecular biology relevant to genetic medicine. In addition, it provides a review of specific human disorders that the author has encountered during her career, as well as an analysis of the progress in determining disease mechanisms and improving therapies.

The chapters in this book provide insights into the processes of research and discovery, as well as how elucidation of disease mechanisms translates into research in diagnostics and treatments.

The book provides historical information and current information obtained from recent journals and presentations, on each of the topics discussed.

Contents:

• Cells and Organelles
• Proteins
• Insights Gained from Studies of Rare Diseases
• Genes and Genomes, Individuals and Populations
• Metabolism and Genetic Variation
• Congenital Malformations and Developmental Deffects
• Receptors and Signaling
• Immune Response, Autoimmune Diseases, and Therapeutic Relevance of Immunity
• Cancer
• Gaps in Progress
• Late-onset Neurodegenerative Diseases
• Gene Therapy Antisense Therapy and Gene Editing
• A New Era in Medicine

Readership: Undergraduate and graduate students and academics in molecular biology and medicine.Discovery;Translation Processes;Genes;Genomes Proteins;Metabolism;Cancer;Neurodegenerative Disease;Immune Response;Proteins;Personalized Medicine;Psychiatric Disorders00

Chapter 1

Cells and Organelles

It is the cells, which create and maintain in us, during the span of our lives, the will to survive, to search, to experiment and to struggle. Life, this anti-entropy, ceaselessly reloaded with energy, is a climbing force toward order amidst chaos toward light among the darkness of the indefinite.

Albert Claude, Nobel lecture, 1974

1.1Early History

In 1665, Robert Hooke published Micrographia. In this book, he presented images of cork. The structure of cork gave hints of compartments with walls. These images are interpreted by some as the first image of cells. Theodor Schwann in 1839 presented information from microscopy that membranes bound specific entities; he proposed that the interior of these entities arose from an amorphous fluid, and that a process of inorganic crystallization occurred in cells. However, the cell theory and the postulation of the cell as a basic unit of tissues came much later.

The origin of the cell theory is frequently attributed to Rudolf Virchow. However, some claim that the cell theory originated with John Goodsir (1845) and Robert Remak (1862). Sherwin Nuland emphasized in a chapter entitled “The fundamental unit of life” (1995) that Virchow was certainly the individual who most strongly promoted the cellular theory. In his text, Cellular Pathology (1863), Virchow presented incontrovertible evidence of the importance of the cell in the understanding of human disease. In the introduction to that text that was based on lectures given in Berlin, Virchow stated that he sought “to offer in a better arranged form than had hitherto be done, a view of the cellular nature of all vital processes, both physiological and pathological, animal and vegetable.” It is interesting to note that Virchow dedicated Cellular Pathology to John Goodsir.

The dawn of cell biology

Detailed analysis of cell morphology through electron microscopy began in the 1940s following the development of electron microscopy and its application to cell analysis by scientists including Keith Robert Porter.

In 1940 Svedberg and Petersen described the use of the ultra-centrifuge and different levels of centrifugal force to separate distinct fractions of molecules of different size and molecular weight.

Albert Claude, Christian de Duve, and George Palade worked in the laboratory at Rockefeller University during specific periods when Porter was carrying out electron microscopy and when cell fractionation procedures were being carried out using ultra-centrifugation. Porter and Claude collaborated on examining the fine structure of cultured cells. Methods of sectioning tissue and deriving preparations that could be used for analysis of cell organization in tissues were also pioneered by Porter (1945).

In 1974, Claude, de Duve, and Palade were jointly awarded the Nobel Prize in Physiology or Medicine for the contribution to understanding of “the structural and functional organization of the cell. Claude developed cell fractionation procedures using ultra-centrifugation to separate the different components, and biochemical studies were carried out to identify the different components.

In an article written in 1977, in an edition of the Journal of Cell Biology dedicated to Keith Porter, Palade noted that modern cell biology began in the United States in the mid 1940s and was largely due to the development and progress of electron microscopy pioneered by Porter.

Palade later wrote of the early years of cell biology in the Porter laboratory at Rockefeller University: “After so many years it is difficult to capture in words the atmosphere of intense activity, remarkable achievements, great excitement, and unlimited optimism that prevailed in that laboratory.”

1.2Endoplasmic Reticulum

In his Nobel lecture (1974) Palade noted that one cellular component separated by ultra-centrifugation was initially identified as “the small particle component,” later as the ribosome component, and still later as the endoplasmic reticulum. Palade and co-workers undertook analyses of the endoplasmic reticulum. Palade participated in studies of the endoplasmic reticulum in pancreatic acinar cells to analyze the process of secretion of pancreatic enzymes. Through use of autoradiography experiments with radiolabeled amino acids, they followed the movements of newly synthesized proteins from the polyribosomes attached to the membranes of the rough endoplasmic reticulum to the cisternae of the endoplasmic reticulum. Secretory proteins were shown to move from the cisternae of the endoplasmic reticulum to the Golgi system of the cells. Within the Golgi the material became progressively more glycosylated.

Palade noted that early autoradiography experiments were performed on pigeon livers following feeding of pigeons with radiolabeled amino acids. In later experiments, they incubated tissue slices with radioactive amino acids.

Palade and colleagues demonstrated that transition of material from the endoplasmic reticulum to the Golgi took place in vesicles. Formation and movement of the vesicles were energy-requiring processes that involved adenosine triphosphate (ATP) and ATP synthesis. Palade reported that the material within the vesicles became progressively more concentrated and formed secretory granules. The process of discharge of material in the secretory granules into the acinae and tubules of the pancreas was found to require energy. In addition, specific stimuli were apparently required to promote discharge of material from the secretory granules.

1.3Discovery of Lysosomes and their Functions

In his 1974 Nobel lecture, de Duve described efforts to classify different cellular fractions separated by ultra-centrifugation through assays of different enzymes. Thus, cytochrome oxidase was found to be particularly abundant in a fraction later found to be rich in mitochondria. Although acid phosphatase was found to be present in low amounts in the cell homogenate prior to ultra-centrifugation, it seemed to disappear and could not readily be detected in any of the fractions derived from ultracentrifugation. However, one particular fraction derived following ultra-centrifugation, yielded acid phosphatase after being stored in the refrigerator for a few days. In follow-up studies, acid phosphatase was found to be present in enclosed sac-like particles. The material inside these sacs was found to be acidic and to contain hydrolase enzymes that functioned optimally at the low pH. One of these hydrolases, alpha glucosidase, turned out to be capable of hydrolyzing a specific form of glycogen and was shown by Hers in 1963 to be deficient in a specific form of glycogen storage disease. Hers therefore described the first lysosomal inborn error of metabolism. In 1963, the first Lysosomal Storage Disease Symposium was organized by the Ciba foundation.

Subsequent progress on understanding lysosomal function and lysosomal storage diseases

Earlier studies on lysosomes emphasized their role in receiving material for degradation through the process of endocytosis. Studies focused particularly on the roles of hydrolases in the lysosomal interior in degrading the imported material. Importantly, deficiencies of specific lysosomal hydrolases were found to be associated with metabolic diseases, characterized by abnormal storage of particular forms of macromolecules.

It is interesting to note that for a number of the diseases that were subsequently shown to be lysosomal storage diseases, there had been detailed descriptions of the clinical manifestation of these diseases many decades before the specific enzyme deficiencies were characterized. Clinical manifestations of Tay Sachs disease were described by Tay in 1881 and by Sachs in 1887. The enzyme defect in Tay Sachs disease was reported by Okada and O’Brien in 1969, and it turned out to be a defect in the gene that encodes the alpha subunit of the beta hexosaminidase gene. The HexA gene that encodes this alpha subunit of beta hexosaminidase was cloned by Proia and Soravia in 1987, and was mapped to chromosome 15q23-q24 by Takeda et al. in 1990.

Gaucher disease was first described in 1882 by a French medical student, Phillipe Gaucher. The enzyme defect in Gaucher disease, deficiency of glucosylceramide beta glucosidase, was discovered by Brady and by Patrick in 1965. The gene that encodes this enzyme was mapped to chromosome 1q by Devine et al. in 1982.

Lysosomal membranes and lysosomal biogenesis

Earlier studies on lysosomes emphasized their role in receiving material for degradation through the process of endocytosis, and studies focused particularly on the roles of hydrolases in the lysosome interior in the degradation of imported material. Deficiency of a specific lysosomal hydrolase was found to be associated with abnormal storage of particular macromolecules and with specific storage diseases.

Studies on lysosome biogenesis have revealed that many of the components of the lysosome are derived from endosomes.

In recent years, evidence has been obtained for passage of components out of the lysosomes and to processes whereby lysosomal membranes fuse with other membranes, e.g. the plasma membrane of the cell. Additionally, there is now evidence for the occurrence of lysosome-related organelles that contain specific lysosomal proteins in addition to organelle-specific proteins (Saftig and Klumperman, 2009). Lysosome-related organelles include compartments that contain major histocompatibility complex II (MHC II) proteins. In addition, there are lysosomal-related organelles involved in cholesterol trafficking, and lysosomal-related organelles that play roles in the repair of plasma membranes.

Melanosomes are lysosome-related organelles. They originate as vesicles within early endosomes and then undergo maturation through delivery of melanogenic enzymes, proteins, and transporters. Key proteins imported include the enzyme tyrosinase (TYR), tyrosinase-related protein (TYRP1) and OCA2, a membrane protein involved in transport (Sitaram and Marks, 2012).

In recent years there has also been increased focus on lysosomal membrane components; these include lysosome-associated membrane proteins (LAMPS), lysosome-integrated membrane proteins (LIMPS), and tetraspanins (Schwake et al., 2012).

In addition to diseases that arise secondary to defects in lysosomal hydrolases there is evidence that specific diseases arise as a result of defects in the lysosomal membrane.

There is now evidence that lysosomal membrane proteins are highly glycosylated. The interior surfaces of the lysosomal membranes are lined by a so-called glycocalyx that shields the membrane from damage by the acid pH and the hydrolytic enzymes in the interior of the lysosome. The integral lysosomal membranes play an important role in forming the glycocalyx. Schwake et al. (2013) reviewed the specific components in lysosome membrane proteins that facilitate the transfer of metabolites and ions into the interior of the lysosomes. They emphasized the role pf the V Type H⁺ ATPase that plays a role in transporting protons into the interior of the lysosome to achieve the acid pH. They noted that the export of protons out of the lysosome was accomplished through the CL7 chloride transporter that exported H⁺ protons and imported chloride ions. A specific lysosomal membrane protein, CD63, facilitated fusion of segments of the lysosome membrane segments with the plasma membrane in the exocytosis process.

The V Type H⁺ ATPase protein on the lysosomal membrane was shown to interact with the mTORC1 complex, and this interaction likely plays an important role in nutrient sensing and in determining whether the cell will participate in anabolic or catabolic processes that involve breakdown of cellular components to provide energy.

The protein cystinosin within the lysosomal membrane facilitates transport of cysteine out of the lysosome. A lysosomal membrane protein, LMBRD1, exports cobalamin Vitamin B12 out of the lysosome. Specific inborn errors of Vitamin B12 metabolism have been shown to be due to defective transport of vitamin B12 out of the lysosome (Coelho et al., 2012).

The LIMP2 protein, also known as SCARB2, is important in transporting the enzyme beta glucocerebrosidase into the lysosome. This import system is not dependent on the mannose-6-phosphate receptor (Coutinho et al., 2012).

One of the f...

Table of contents

• Cover
• Halftitle
• Series Editors
• Title
• Copyright
• Preface
• Acknowledgements
• Contents
• 1. Cells and Organelles
• 2. Proteins
• 3. Insights Gained from Studies of Rare Diseases
• 4. Genes and Genomes, Individuals and Populations
• 5. Metabolism and Genetic Variation
• 6. Congenital Malformations and Developmental Defects
• 7. Receptors and Signaling
• 8. Immune Responses, Autoimmune Diseases, and Therapeutic Relevance of Immunity
• 9. Cancer
• 10. Gaps in Progress
• 11. Late-onset Neurodegenerative Disorders
• 12. Gene Therapy, Antisense Therapy, and Gene Editing
• 13. A New Era in Medicine
• Index