Collagen

Collagen is the main component of connective tissue and the most abundant protein in the human body. It is mostly found in fibrous tissues such as tendons, ligaments and skin.

Types

 * Type I: skin, tendon, vasculature, organs, bone (main component of the organic part of bone)
 * Type II: cartilage (main collagenous component of cartilage)
 * Type III: reticulate (main component of reticular fibers), commonly found alongside type I.
 * Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane.
 * Type V: cell surfaces, hair, and placenta

Components
Collagen is made up primarily of glycine and proline.

Co-factors
Vitamin C is a co-factor of many of the chemical reactions involved in collagen production. Vitamin C is also a mast cell stabilizer. Deficiency can result in impaired collagen synthesis and scurvy.

Pathogens and collagen degradation
Infection can degrade collagen via direct secretion of collagenases and other enzymes (in the case of bacteria) or increased host production of matrix metalloproteinaises (MMPs) as part of the normal immune response (in the case of bacteria and viruses). Numerous bacteria secrete their own collagenases. Borrelia spirochetes upregulate production of human collagenase (MMP-1) and gelatinase B (MMP-9), an enzyme that can degrade both elastin and collagen. MMP-8 and MMP-9 are upregulated in bacterial meningitis and the latter is associated with an increased risk of blood-brain barrier breakdown and neurological sequale such as epilepsy and cognitive impairment. Herpes simplex virus, HHV-6 and Coxsackie B infection result in increased production of MMP-9, which is associated with Type IV and Type V collagen degradation. Coxsackie B has also been associated with increased production of other MMPs.

Infection and Ehlers-Danlos Syndrome
Ehlers-Danlos Syndrome is a group connective tissue disorders caused by genetic defects in the production of collagen. Type III, hypermobile EDS (hEDS), is also thought to be genetic but as a genetic marker has not yet been identified, it is diagnosed via signs and symptoms. A case study of a patient who met the diagnostic criteria for hEDS and had a chronic Bartonella infection found their hEDS symptoms resolved with antibiotic treatment for Bartonella. Mycoplasma pneumoniae has been associated with mitral valve degeneration, a complication of EDS.

Fluoroquinolone antibiotics
“Fluoroquinolones upregulate cell matrix metalloproteinases, resulting in a reduction of collagen fibrils of types I and III collagen.” A longitudinal study found Fluoroquinolones increased the risk of collagen-related adverse events like tendon ruptured and detached retinas. In December 2018, the FDA recommended against its use in patients with connective tissue disorders like Ehlers-Danlos Syndrome and Marfan Syndrome.

ME/CFS
Preliminary data from the UK ME/CFS biobank show an association between increased risk of ME/CFS and a gene variant that encodes for a subunit of prolyl 4-hydroxylase subunit alpha 1 (P4HA1), which encodes for procollagen-proline dioxygenase, an enzyme involved in the production of collagen that also plays a role in the regulation of energy metabolism via downregulation of pyruvate dehydrogenase. The data are based on self-reported diagnosis of chronic fatigue syndrome and involve a sample size that is very small for genome-wide association studies (n=1829), making confidence intervals difficult to estimate.

As a supplement
When hydrolyzed, collagen is reduced to small peptides, which can be ingested in the form of dietary supplement or functional foods and beverages with the intent to aid joint and bone health and enhance skin health. These hydroxyproline-containing peptides are transported into the target tissues (e.g., skin, bones, and cartilage), where they act as building blocks for local cells and help boost the production of new collagen fibers.