The Human Micro Biome

There is a growing recognition that we as a species, humans that is, are not a single organism but a community of organisms living in synchrony. As scientists have recognized for many years, the human gut, skin, and digestive tract are colonized by trillions of bacteria, fungi and other microbes. What we did not realize until recently, was how important these organisms are to our health and well-being

The microenvironment of the human gastrointestinal tract reflects the interplay between bacteria, our diet, intestinal digestive enzymes, lipids, polysaccharides, amino acids, and the by-products of metabolism. The specific make-up of each individual reflects their environment, diet, and family heritage. Indeed, our bacterial flora are transmitted to us by our mothers, who prior to the advent of pasteurized baby-foods, pre-chewed their infant’s food.

More to the point, we now realize that bacterial infections and exposures to foreign antigens early in life protect and prepare us for a healthy adult life. Many modern maladies, such as asthma, diabetes, hypertension, even possibly autism and schizophrenia, may reflect infections, immune responses and the timing thereof. It has been suggested that infections with parasites modulate our immune response. In our increasingly clean environment, devoid of hookworms, tapeworms, and the like, our overactive immune system creates autoimmunity in the form of rheumatoid arthritis, systemic lupus and other maladies.

This reflects the growing recognition that human biology is in fact human ecology. The importance of this cannot be overstated when we examine human tumor biology. We are continually bombarded by the teachings of a cadre of scientists who believe whole heartedly that they can answer the puzzle of human cancer by examining the intricacies of individual human cancer cells, primarily at the level of DNA.  Nothing could be further from the truth.

Take for example just one of the myriad of signaling pathways. Beta catenin is among the most potent tumor promoters. The deranged function of beta-catenin has been identified in several human tumors including prostate, lung and colon. Its closest association being that with colon cancer, wherein the loss of the APC protein (adenomatous polyposis coli), results in a particularly aggressive form of the disease.  The APC protein normally combines with axin and glycogen synthase kinase 3 beta (GSK3B) which all together function to regulate beta-catenin. It is the loss of APC that releases Beta-catenin and drives polyps to become cancerous.

However, upstream of this triumvirate of regulatory proteins are the integrin-ca cadherin proteins that communicate across the cell membrane. By changing the environment of the colon itself, we can influence the integrins, which regulate the cadherins. This in turn regulates beta catenin.  Thus, colon cancer may not arise from changes in our genetic makeup but instead may be driven by micro-environmental changes in the colonic milieu that alter cellular behavior and drive malignant transformation.

Again and again, we are forced to recognize the complexity of human biology. Now we realize that it is not just the genome to the transcriptome to the proteome, but indeed the micro biome.